Pediatric and adult Chiari malformation Type I surgical series 1965–2013: a review of demographics, operative treatment, and outcomes

Full access

OBJECT

Chiari malformation Type I (CM-I) is a hindbrain disorder associated with elongation of the cerebellar tonsils, which descend below the foramen magnum into the spinal canal. It occurs in children and adults. Clinical symptoms mainly develop from alterations in CSF flow at the foramen magnum and the common subsequent development of syringomyelia.

METHODS

The authors reviewed English-language reports of pediatric, adult, and combined (adult and pediatric) surgical series of patients with CM-I published from 1965 through August 31, 2013, to investigate the following: 1) geographical distribution of reports; 2) demographics of patients; 3) follow-up lengths; 4) study durations; 5) spectrum and frequency of surgical techniques; 6) outcomes for neurological status, syrinx, and headache; 7) frequency and scope of complications; 8) mortality rates; and 9) differences between pediatric and adult populations. Research and inclusion criteria were defined, and all series that contained at least 4 cases and all publications with sufficient data for analysis were included.

RESULTS

The authors identified 145 operative series of patients with CM-I, primarily from the United States and Europe, and divided patient ages into 1 of 3 categories: adult (> 18 years of age; 27% of the cases), pediatric (≤ 18 years of age; 30%), or unknown (43%). Most series (76%) were published in the previous 21 years. The median number of patients in the series was 31. The mean duration of the studies was 10 years, and the mean follow-up time was 43 months. The peak ages of presentation in the pediatric studies were 8 years, followed by 9 years, and in the adult series, 41 years, followed by 46 years. The incidence of syringomyelia was 65%. Most of the studies (99%) reported the use of posterior fossa/foramen magnum decompression. In 92%, the dura was opened, and in 65% of these cases, the arachnoid was opened and dissected; tonsillar resection was performed in 27% of these patients. Postoperatively, syringomyelia improved or resolved in 78% of the patients. Most series (80%) reported postoperative neurological outcomes as follows: 75% improved, 17% showed no change, and 9% experienced worsening. Postoperative headaches improved or resolved in 81% of the patients, with a statistical difference in favor of the pediatric series. Postoperative complications were reported for 41% of the series, most commonly with CSF leak, pseudomeningocele, aseptic meningitis, wound infection, meningitis, and neurological deficit, with a mean complication rate of 4.5%. Complications were reported for 37% of pediatric, 20% of adult, and 43% of combined series. Mortality was reported for 11% of the series. No difference in mortality rates was seen between the pediatric and adult series.

CONCLUSIONS

Before undergoing surgical treatment for CM-I, symptomatic patients and their families should be given clear information about the success of treatment and potential complications. Furthermore, surgeons may benefit from comparing published data with their own. In the future, operative CM-I reports should provide all details of each case for the purpose of comparison.

ABBREVIATIONSBMI = body mass index; CM-I = Chiari malformation Type I; IQR = interquartile range.

Abstract

OBJECT

Chiari malformation Type I (CM-I) is a hindbrain disorder associated with elongation of the cerebellar tonsils, which descend below the foramen magnum into the spinal canal. It occurs in children and adults. Clinical symptoms mainly develop from alterations in CSF flow at the foramen magnum and the common subsequent development of syringomyelia.

METHODS

The authors reviewed English-language reports of pediatric, adult, and combined (adult and pediatric) surgical series of patients with CM-I published from 1965 through August 31, 2013, to investigate the following: 1) geographical distribution of reports; 2) demographics of patients; 3) follow-up lengths; 4) study durations; 5) spectrum and frequency of surgical techniques; 6) outcomes for neurological status, syrinx, and headache; 7) frequency and scope of complications; 8) mortality rates; and 9) differences between pediatric and adult populations. Research and inclusion criteria were defined, and all series that contained at least 4 cases and all publications with sufficient data for analysis were included.

RESULTS

The authors identified 145 operative series of patients with CM-I, primarily from the United States and Europe, and divided patient ages into 1 of 3 categories: adult (> 18 years of age; 27% of the cases), pediatric (≤ 18 years of age; 30%), or unknown (43%). Most series (76%) were published in the previous 21 years. The median number of patients in the series was 31. The mean duration of the studies was 10 years, and the mean follow-up time was 43 months. The peak ages of presentation in the pediatric studies were 8 years, followed by 9 years, and in the adult series, 41 years, followed by 46 years. The incidence of syringomyelia was 65%. Most of the studies (99%) reported the use of posterior fossa/foramen magnum decompression. In 92%, the dura was opened, and in 65% of these cases, the arachnoid was opened and dissected; tonsillar resection was performed in 27% of these patients. Postoperatively, syringomyelia improved or resolved in 78% of the patients. Most series (80%) reported postoperative neurological outcomes as follows: 75% improved, 17% showed no change, and 9% experienced worsening. Postoperative headaches improved or resolved in 81% of the patients, with a statistical difference in favor of the pediatric series. Postoperative complications were reported for 41% of the series, most commonly with CSF leak, pseudomeningocele, aseptic meningitis, wound infection, meningitis, and neurological deficit, with a mean complication rate of 4.5%. Complications were reported for 37% of pediatric, 20% of adult, and 43% of combined series. Mortality was reported for 11% of the series. No difference in mortality rates was seen between the pediatric and adult series.

CONCLUSIONS

Before undergoing surgical treatment for CM-I, symptomatic patients and their families should be given clear information about the success of treatment and potential complications. Furthermore, surgeons may benefit from comparing published data with their own. In the future, operative CM-I reports should provide all details of each case for the purpose of comparison.

A Chiari malformation Type I (CM-I) is a craniocervical junction disorder that is associated with deformity and elongation of the cerebellar tonsils and is specifically characterized by tonsils' descent of more than 5 mm below the foramen magnum into the spinal canal. It occurs in children and adults and was first described by an Austrian pathologist, Hans Chiari, in 1891. The essential element in the pathophysiology of clinical symptoms is a change in the flow of CSF at the level of the foramen magnum, which is frequently associated with the subsequent development of syringomyelia.10

The incidence of tonsillar ectopia and CM-I has been reported to be 0.5%–3.5% in general, 0.56%–0.77% on MRI studies, and 0.62% in anatomical dissection studies,20‌,98‌,99‌ which means that it is quite common in the general population. There seems to be a slight female predominance of cases (1.3:1), and the association with syringomyelia has been reported to range widely, from 30% to 70%.90‌,127‌ Suboccipital craniectomy and foramen magnum decompression, with or without dural opening and with or without arachnoid opening or dissection, have been used most commonly for surgical treatment but without a clear idea of the frequency of use of either procedure in the reported series. Furthermore, it has not been noted whether a difference exists in the operative techniques used for pediatric and adult patients. Other factors that are also unclear are as follows: the geographical distribution of reports in the literature; the demographics of patients, including sex and age; the length of follow-up; the duration of study periods; the spectrum and frequency of surgical techniques used; neurological outcomes; improvements in outcomes for syrinx and headache; the frequency and scope of complications; mortality rates; and any differences between pediatric and adult populations with this malformation.

For this study, we reviewed the reports of pediatric, adult, and combined (adult and pediatric) surgical series of patients with CM-I published from 1965 through August 31, 2013, to delineate the timeline of the reported series and the number of reported patients and to investigate the factors listed above.

Methods

For this study, we searched PubMed/Medline for English-language reports of CM-I series (adult and pediatric) through August 31, 2013, using the key words “Chiari I malformation,” “adult,” “pediatric,” and “series.” In addition, we used references from these publications with the key term “Chiari I malformation” to locate series that did not have adequate key words to locate such reports in PubMed/Medline.

The research and inclusion criteria were defined before the study. We included series that contained at least 4 cases of CM-I and all publications with sufficient data for meaningful analysis. Certain series were published by the same authors at different times. To avoid an overlap of cases in the analysis, we included only the most recent publications of these authors if they were reports of consecutive series. If the same author(s) published different series, these were also included in the analysis. Two authors were involved in the study selection and 2 others in data extraction, with conference to determine consensus for discrepancies.

We excluded series of patients with achondroplasia, craniosynostosis, or combined Chiari Type I and II malformations that could not be mutually differentiated. We also excluded series in which patients with CM-I and syringomyelia were combined with patients whose syringomyelia was of a different origin and who therefore could not be mutually distinguished. In addition, we excluded patients with syringomyelia without CM-I, patients with acquired CM-I (i.e., after lumbar drainage), and series of patients with other congenital craniocervical malformations dominating, in addition to CM-I, with unclear mutual differentiation.

We analyzed the published CM-I series according to the year of publication and the country and continent of origin, and we categorized the cohort of patients into 1 of 3 groups: adult (> 18 years of age), pediatric (≤ 18 years of age), and combined/unknown. The lengths of follow-up were analyzed, including the medians and ranges. All the series were also analyzed according to age and sex distributions, and we determined the ranges, means, and standard deviations of these data. All the data were tabulated.

Operative treatment techniques were analyzed for the adult, pediatric, and combined patient cohorts, including suboccipital/foramen magnum decompression, dural opening, arachnoid opening, tonsillar resection, and CSF shunting. Among the adult, pediatric, combined, and total patient populations, postoperative improvement or resolution of suboccipital headache was analyzed when data were provided. Migraine headaches, neck pain, and other pain categories were not included. Postoperative neurological outcomes were most commonly listed as improvement/resolution, no change, or worsening. These outcomes in the adult, pediatric, combined, and total patient cohorts were examined separately. Postoperative syringomyelia outcomes were most commonly listed as improvement/resolution or no change. These outcomes in adult, pediatric, combined, and total patient cohorts were analyzed separately. Series that provided details of complications were analyzed for the adult, pediatric, and combined patient cohorts. Ranges and means of these data were noted, and series mortality rates were analyzed when they were provided in the report.

The frequency in differences of the investigated variables between the adult and pediatric series was determined with a chi-square or Fisher exact test. A 2-sided p value of < 0.05 was considered to be statistically significant. The Statistica for Windows 2005 program package version 7.1 (StatSoft, Inc.) was used for statistical analysis of the data.

Results

General Information

In the English-language literature published over a span of 48 years (1965–2013), we identified a total of 145 series of patients with CM-I, which included adult, pediatric, and combined adult and pediatric series (referred to here as combined series), in addition to series in which patient ages were not provided.1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ In this same span of published articles, we identified 40 series (27%) of adult patients4‌,8‌,13‌,14‌,16‌–19‌,21‌,22‌,29‌,36‌,45‌,48‌,49‌,57‌,58‌,62‌,71‌,78‌,79‌,82‌,84‌,85‌,88‌,95‌,105‌,113‌,118‌–120‌,122‌–125‌,128‌,137‌,146‌,149‌,151‌ and 39 series (27%) of pediatric patients1‌–3‌,15‌,24‌,28‌,30‌–33‌,35‌,41‌,42‌,50‌,51‌,54‌,56‌,60‌,61‌,65‌,77‌,80‌,81‌,86‌,89‌,92‌,93‌,97‌,104‌,108‌,109‌,116‌,133‌,134‌,143‌,145‌,150‌,154‌,155‌ (Fig. 1‌). Combined series, which included both pediatric and adult patients, constituted 61 reports (42%).5‌–7‌,9‌,11‌,12‌,25‌–27‌,34‌,37‌,38‌,40‌,43‌,44‌,46‌,47‌,52‌,53‌,55‌,63‌,66‌,67‌,70‌,73‌,74‌,76‌,83‌,87‌,90‌,91‌,94‌,96‌,100‌,102‌,103‌,106‌,110‌,111‌,114‌,115‌,117‌,121‌,126‌,127‌,129‌,130‌,132‌,135‌,138‌–142‌,144‌,147‌,148‌,156‌–159‌ We also identified 5 series (3%) in which the patients' ages could not be identified.23‌,37‌,39‌,59‌,107‌ The median number of patients in each series was 31 (interquartile range [IQR] 15–68) and ranged from 4 to 585.

FIG. 1.
FIG. 1.

Age distribution of patients in the CM-I operative series.

The durations of the studies ranged from 1 to 38 years, with a mean of 10 years (IQR 4–12 years). In the studies with pediatric patients, the mean study duration was 10 years (range 1–23 years), whereas in the studies with adult patients, the mean duration was 8 years (range 2–30 years). In the combined, pediatric, and adult series, the study durations had a mean of 11 years (range 1–38 years). The mean follow-up time of patients in all studies was 43 months (range 2–168 months). These data are shown in Table 1‌.

TABLE 1

Follow-up times

Study TypeFollow-Up Time (mos)
Mean (SD)Min/MaxMedianIQR
Adult series46 (31.5)3/1512814–52
Pediatric series37 (26.8)2/1203916–49.5
Combined series39 (36.3)6/1684017.5–60.5
Total43 (35.2)2/1683917–51

The largest number of studies was published over the past 21 years, from 1993 to 2013 (111 [77%] of 145 studies) (Fig. 2‌).

FIG. 2.
FIG. 2.

Number of CM-I operative studies according to the year of publication.

Geographical Distribution

The great majority of CM-I series were published in the United States,1‌–3‌,5‌,6‌,8‌,9‌,15‌,16‌,18‌,19‌,22‌,24‌,25‌,27‌,30‌,31‌,33‌,35‌,38‌,41‌–43‌,46‌,50‌–54‌,56‌,59‌,62‌,65‌,71‌,73‌,74‌,76‌,78‌,80‌,86‌,88‌–90‌,92‌,93‌,97‌,100‌,105‌–110‌,115‌,116‌,119‌,122‌,124‌,127‌,132‌,133‌,143‌,150‌,151‌,154‌,155‌,157‌ followed by Great Britain,7‌,39‌,40‌,70‌,91‌,94‌,96‌,102‌,103‌,117‌,126‌,129‌,134‌,138‌ Italy,28‌,36‌,57‌,60‌,114‌,118‌,120‌,137‌,141‌,145‌,149‌ France,14‌,29‌,47‌,61‌,67‌,104‌,111‌,135‌ and Japan.55‌,75‌,79‌,113‌,128‌,130‌,139‌,142‌ There were 5 publications each from Spain,58‌,121‌,146‌–148‌ Germany,4‌,13‌,32‌,82‌,83‌ and Turkey48‌,49‌,84‌,85‌,156‌ and 4 publications from Brazil.12‌,26‌,125‌,140‌ Three studies each were from Canada44‌,77‌,95‌ and China.66‌,158‌,159‌ Poland,21‌,87‌ Belgium,34‌,123‌ and India11‌,63‌ each had 2 publications. The remaining countries published a report on 1 series each17‌,23‌,37‌,45‌,81‌,144‌ (Figs. 3‌ and 4‌).

FIG. 3.
FIG. 3.

Number of operative CM-I studies according to the country of publication.

FIG. 4.
FIG. 4.

Distribution of CM-I studies according to the continent of publication.

Demographics

The total number of patients in all the published series was 8605: 2351 adult (27%), 2583 pediatric (30%), and 3671 unknown (43%)1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ (Fig. 5‌).

FIG. 5.
FIG. 5.

Age distribution of patients with CM-I.

In the adult-only series,4‌,8‌,13‌,14‌,16‌–19‌,21‌,22‌,29‌,36‌,45‌,48‌,49‌,57‌,58‌,62‌,71‌,78‌,79‌,82‌,84‌,85‌,88‌,95‌,105‌,113‌,118‌–120‌,122‌–125‌,128‌,137‌,146‌,149‌,151‌ there were 1608 patients: 543 men (34%), 913 women (57%), and 152 (9%) of unknown sex.

In the pediatric-only series, there were 2302 patients: 578 boys (25%), 635 girls (28%), and 1089 (47%) of unknown sex.1‌–3‌,15‌,24‌,28‌,30‌–33‌,35‌,41‌,42‌,50‌,51‌,54‌,56‌,60‌,61‌,65‌,77‌,80‌,81‌,86‌,89‌,92‌,93‌,97‌,104‌,108‌,109‌,116‌,133‌,134‌,143‌,145‌,150‌,154‌,155

In the published series, cases in females predominated over those in males (39% vs 29%, respectively); there were 57% women versus 34% men in the adult series and 28% girls versus 25% boys in the pediatric series (p < 0.001, Fisher exact test) (Fig. 6‌).

FIG. 6.
FIG. 6.

Sex distribution of patients with CM-I.

The median age of adult patients was 40.5 years (IQR 37–45.3 years), of pediatric patients, 8 years (IQR 6–10.5 years), and in the combined studies, 35 years (IQR 27.3–40 years) (Table 2‌). There were 2 peak ages of presentation in both the pediatric and the adult series. The most common (peak) age presentation in the pediatric series was 8 years, followed by 9 years (Fig. 7‌ upper). The most common (peak) age presentation in the adult series was 41 years, followed by 46 years (Fig. 7‌ lower).

TABLE 2

Patient ages in CM-I studies

Study TypePatient Age (yrs)
Mean (SD)Min/MaxMedianIQR
Adult series40.9 (5.9)18/7240.537–45.3
Pediatric series7.7 (3)0.25/1886–10.5
Combined series33 (12)0.3/703527.3–40
Total27 (8)0.25/723627–40
FIG. 7.
FIG. 7.

Upper: Scatter plot graph of the presentation ages of patients with CM-I in the pediatric series. Lower: Scatter plot graph of the presentation ages of patients in the adult series.

Incidence of Syringomyelia

Of a total of 6347 patients in all operative series for whom an association with a syrinx was reported, 4144 (65%) harbored a spinal cord syrinx. The range of syringomyelia in this series ranged from 12% to 100%. The incidence of syringomyelia ranged from 20% to 100% in the adult series, 12% to 100% in the pediatric series, and 32% to 100% in the combined series1‌–4‌,6‌–9‌,12‌–19‌,21‌–25‌,27‌–37‌,40‌–42‌,45‌–58‌,60‌–63‌,65‌–67‌,70‌,71‌,73‌–77‌,79‌,81‌–87‌,89‌,92‌–97‌,100‌,102‌–106‌,108‌–111‌,113‌–115‌,117‌–130‌,132‌–135‌,137‌,139‌,140‌,142‌–151‌,154‌,155‌,157‌–159‌ (Table 3‌).

TABLE 3

Incidence of syringomyelia in CM-I operative series

Study TypeNo. (%)Range (%)
Adult series1090/1578 (69)20–100
Pediatric series673/1678 (40)12–100
Combined series4144/6347 (65)32–100

In the adult series that reported syrinx association, 1090 (69%) of 1578 patients had a syrinx.4‌,8‌,13‌,14‌,16‌–19‌,21‌,22‌,29‌,36‌,45‌,48‌,49‌,57‌,62‌,71‌,79‌,82‌,84‌,85‌,95‌,105‌,113‌,118‌–120‌,122‌–125‌,127‌,128‌,137‌,149‌,151‌ In the pediatric series that reported an association of syringomyelia, of a total of 1678 patients, 673 (40%) harbored a syrinx.1‌–3‌,15‌,24‌,28‌,30‌–33‌,35‌,41‌,42‌,50‌,51‌,54‌,56‌,60‌,61‌,65‌,77‌,81‌,86‌,89‌,92‌,93‌,97‌,100‌,104‌,108‌,109‌,133‌,134‌,145‌,150‌,154‌,155‌ In the combined series that reported this association, of a total of 3091 patients, 2411 (78%) had a syrinx.6‌,7‌,9‌,12‌,23‌,25‌,27‌,34‌,37‌,40‌,46‌,47‌,52‌,53‌,55‌,58‌,63‌,66‌,67‌,70‌,74‌–76‌,87‌,94‌,96‌,100‌,102‌,103‌,106‌,110‌,111‌,114‌,115‌,117‌,121‌,126‌,129‌,130‌,132‌,135‌,138‌–140‌,142‌–144‌,147‌,148‌,157‌–159‌ Significantly more common was the incidence of syringomyelia in the adult series (p < 0.001, Fisher exact test) (Fig. 8‌).

FIG. 8.
FIG. 8.

Incidence of syringomyelia in patients in the CM-I operative series.

Operative Techniques

Of a total of 140 adult, pediatric, and combined studies (5 of 145 series were unknown and, thus, not included),1‌–9‌,11‌–19‌,21‌,22‌,24‌–36‌,38‌,40‌–58‌,60‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–106‌,108‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ only 4 did not describe the operative techniques used. Of the 136 series that reported operative techniques, 134 (99%) reported the use of posterior fossa/foramen magnum decompression. In 123 (92%), the dura was opened. In 81 (66%) of these studies, the arachnoid was opened and dissected, and in 22 (27%) of these 81, tonsillar resection was performed, whereas some sort of syrinx shunting was carried out in 25 patients.

Of 39 pediatric series,1‌–3‌,15‌,24‌,28‌,30‌–33‌,35‌,41‌,42‌,50‌,51‌,54‌,56‌,60‌,61‌,65‌,77‌,80‌,81‌,86‌,89‌,92‌,93‌,97‌,104‌,108‌,109‌,116‌,133‌,134‌,143‌,145‌,150‌,154‌,155‌ 38 (97%) delineated the operative techniques used. Of these, 37 studies (97%) described the use of posterior fossa decompression. One study each (2.7%) reported the use of endoscopic decompression, tonsillectomy without craniectomy, and cranioplasty after decompression. Of 37 studies involving posterior fossa decompression, 30 (81%) reported dural opening, and of them, 14 (47%) added arachnoid opening and dissection. In 4 series, some sort of shunting procedure was added. Six (43%) of the 14 studies that described arachnoid opening and dissection added tonsillar resection as well.

Of 40 adult series,4‌,8‌,13‌,14‌,16‌–19‌,21‌,22‌,29‌,36‌,45‌,48‌,49‌,57‌,58‌,62‌,71‌,78‌,79‌,82‌,84‌,85‌,88‌,95‌,105‌,113‌,118‌–120‌,122‌–125‌,128‌,137‌,146‌,149‌,151‌ 37 (93%) reported the operative techniques used. All of them described the use of posterior fossa decompression. All but 1 reported dural opening (97.3%), and 3 studies (8%) reported only dural relaxation incisions. Of all the series that reported the use of posterior cranial fossa/foramen magnum decompression, 26 (70%) added arachnoid opening and dissection, and of them, 6 (23%) added tonsillar resection. In 2 series, syrinx shunting was also reported.

All 61 combined series5‌–7‌,9‌,11‌,12‌,25‌–27‌,34‌,37‌,38‌,40‌,43‌,44‌,46‌,47‌,52‌,53‌,55‌,63‌,66‌,67‌,70‌,73‌,74‌,76‌,83‌,87‌,90‌,91‌,94‌,96‌,100‌,102‌,103‌,106‌,110‌,111‌,114‌,115‌,117‌,121‌,126‌,127‌,129‌,130‌,132‌,135‌,138‌–142‌,144‌,147‌,148‌,156‌–159‌ reported the operative techniques used. All but 1 of these (98%) reported the use of suboccipital craniectomy/posterior fossa decompression/foramen magnum decompression. Only 1 reported syrinx shunting. Of all the series using suboccipital craniectomy/foramen magnum decompression, the dura was opened in 57 (95%) of the studies, and of these 57, 41 (72%) reported arachnoid opening/dissection. Of the 41 studies that reported arachnoid opening/dissection, 10 (24%) added tonsillar resection. Shunting of the syrinx was performed in 25 patients (Table 4‌).

TABLE 4

Distribution of operative techniques in CM-I

Technique UsedAdult Series (n = 40) (no./total no. [%])Pediatric Series (n = 39) (no./total no. [%])Combined Series (n = 61) (no./total no. [%])
Operative technique37/40 (93)38/39 (97)61/61 (100)
Posterior fossa/foramen magnum decompression37/37 (100)37/38 (97)60/61 (98)
Dural opening/duraplasty36/37 (97)30/37 (81)57/60 (95)
Arachnoid opening/dissection26/37 (70)14/30 (47)41/57 (72)
Tonsillar resection6/26 (23)6/14 (43)10/41 (24)
Shunt2/26 (8)4/30 (13)19/60 (32)

Postoperative Syringomyelia Outcomes

Postoperative improvement of syringomyelia was reported for 1108 (78%) of 1423 patients.1‌–4‌,6‌–9‌,12‌–17‌,21‌–25‌,27‌–37‌,40‌–42‌,45‌–58‌,60‌–63‌,66‌,67‌,70‌,73‌–75‌,79‌–87‌,89‌,92‌–94‌,96‌,100‌,102‌–106‌,108‌–111‌,113‌–115‌,117‌,119‌,120‌,122‌–130‌,132‌–135‌,137‌–145‌,147‌–150‌,156‌–159‌ It should be noted that of all the series for which an association of syringomyelia with CM-I was reported, only some postoperative syringomyelia outcomes were reported; hence, there was disproportion between reporting syringomyelia association and syringomyelia outcomes.

In the adult series, syrinx improvement was reported for 293 (78%) of 375 patients with a syrinx. The reported ranges for individual adult series were 38%–100% improvement/resolution, 11%–64% no change, and 2%–40% worsening.

In the pediatric series, improvement/resolution of the syrinx ranged from 50% to 100% of patients; 163 (79%) of 207 patients had syrinx improvement. Patients with no change ranged from 8% to 50%, and an increase in size (worsening) occurred in 5%–12%.

In the combined series, improvement/resolution of the syrinx was reported to range from 39% to 100%, with no change in syrinx size in 3%–42% and an increase in the syrinx size (worsening) in 3%–45%. In these series, syrinx improvement/resolution was reported for 1108 (78%) of 1423 patients. There was no difference in the syrinx improvement/resolution rates between the adult and pediatric series (p = 0.916, Fisher exact test) (Table 5‌, Fig. 9‌).

TABLE 5

Postoperative syringomyelia outcomes in patients with CM-I

Study TypePostop Syrinx Outcomes in % (range)
Improvement/ResolutionNo ChangeWorsening
Adult series38–10011–642–40
Pediatric series50–1008–505–12
Combined series39–1003–423–45
FIG. 9.
FIG. 9.

Distribution of patients with CM-I according to syringomyelia outcome.

Postoperative Neurological Outcomes

The majority of series (116 series [80%]) reported postoperative neurological outcomes as improvement/resolution, no change, and worsening of neurological status. It should be noted that these evaluations were performed subjectively by the treating surgeons and reported by the publications' authors. Of 4206 patients, 3150 (75%) were reported to be improved, 697 (16.6%) had no change in neurological status, and 359 (8.5%) experienced worsening.3‌–7‌,11‌,13‌,15‌,17‌–19‌,21‌–23‌,25‌–37‌,40‌–46‌,48‌,49‌,52‌,54‌–56‌,58‌,59‌,62‌,63‌,65‌–67‌,70‌,71‌,73‌–87‌,89‌–91‌,93‌–97‌,100‌,102‌,105‌,106‌,109‌–111‌,113‌–121‌,123‌–125‌,127‌–130‌,133‌,135‌,137‌–151‌,154‌–159‌ Of 1126 patients in the adult series, improvement/resolution was noted in 823 (73%), no change in 225 (20%), and worsening in 78 (7%). The range of improvement/resolution in individual series was 22% to 100%, no change in status ranged from 4% to 65%, and worsening ranged from 5% to 43%.4‌,13‌,17‌–19‌,21‌,22‌,29‌,36‌,45‌,48‌,49‌,58‌,62‌,71‌,78‌,79‌,82‌,84‌,85‌,95‌,105‌,113‌,118‌–120‌,123‌–125‌,128‌,137‌,149‌,151

The pediatric series reported improvement/resolution of status in individual series ranging from 55% to 100%, no change in 5%–30%, and worsening in 5%–18%. Improvement/resolution was reported for 669 (84%) of 796 patients, no change in 116 (15%), and worsening in 11 (1%).3‌,15‌,28‌,30‌–33‌,35‌,41‌,42‌,54‌–56‌,77‌,80‌,81‌,86‌,89‌,93‌,97‌,109‌,133‌,143‌,145‌,150‌,154‌,155

The combined pediatric and adult series reported improvement/resolution to range in individual series from 27% to 100%, no change to range from 4% to 64%, and worsening to range from in 2% to 45%. In these series, of a total of 2284 patients, improvement/resolution was noted in 1658 (72%), no change in 356 (16%), and worsening in 270 (12%).5‌–7‌,11‌,23‌,25‌–27‌,34‌,37‌,40‌,43‌,44‌,46‌,52‌,55‌,58‌,63‌,66‌,67‌,70‌,74‌–76‌,87‌,90‌,91‌,94‌,96‌,100‌,102‌,106‌,110‌,111‌,114‌,115‌,117‌,121‌,127‌,129‌,130‌,135‌,138‌–140‌,142‌–144‌,147‌,148‌,157‌–159‌ There was significantly greater worsening of neurological outcomes in the adult series than in the pediatric series (p < 0.001, chi-square test) (Table 6‌, Fig. 10‌).

TABLE 6

Postoperative neurological status outcomes in patients with CM-I

Study TypePostop Neurological Outcomes in % (range)
Improvement/ResolutionNo ChangeWorsening
Adult series22–1004–655–43
Pediatric series55–1005–305–18
Combined series27–1004–642–45
FIG. 10.
FIG. 10.

Postoperative distribution of neurological status outcomes according to CM-I series.

Postoperative Headache Outcomes

Postoperative headache outcomes categorized by improvement/resolution were reported for 23 series (16%), in 350 (81%) of a total 433 patients.1‌,2‌,11‌,19‌,32‌,37‌,43‌,55‌,60‌,62‌,70‌,73‌,80‌,86‌,89‌,93‌,108‌,110‌,118‌,127‌,138‌,142‌,150‌ Of a total of 179 pediatric patients, improvement/resolution of headache was noted in 157 (88%). Improvement/resolution in the individual series ranged from 66% to 100%. Of 128 adult patients, improvement/resolution was noted in 93 (73%). In individual pediatric series, improvement/resolution ranged from 37% to 100%, whereas in the combined adult and pediatric series, of 126 patients, improvement/resolution was noted in 100 (79%). In the individual series, it ranged from 12% to 92% (Fig. 11‌). There was a significant difference in improvement/resolution of headache in favor of the pediatric series over that of the adult series (p = 0.001, Fisher exact test).

FIG. 11.
FIG. 11.

Postoperative headache outcomes according to CM-I series.

Postoperative Complications

Postoperative complications were noted in 60 (41%) of 145 series.2‌,4‌,6‌,11‌,12‌,15‌,18‌,19‌,24‌,25‌,29‌,32‌,35‌,38‌,41‌,42‌,44‌,45‌,48‌,49‌,52‌–54‌,56‌,60‌,66‌,70‌,75‌,76‌,82‌,83‌,85‌–88‌,90‌,92‌,93‌,96‌,97‌,104‌–106‌,109‌,115‌–118‌,120‌,126‌,133‌,135‌,140‌,143‌,145‌,146‌,148‌,150‌,155‌,156‌,159‌ In these series, the median complication rate was 4.5% (IQR 3.3%–7%). The complications most commonly reported were CSF leak (range 1% to 24% [median 5%; IQR 2%–10.5%]), pseudomeningocele (range 1%–47% [median 12%; IQR 3%–20%]), aseptic meningitis (range 1%–40% [median 4.5%; IQR 3%–8%]), wound infection (range 1%–11% [median 3%; IQR 2%–5.5%]), meningitis (range 1%–6% [median 3.5%; IQR 2%–6.3%]), neurological deficit (range 1%–8% [median 4%; IQR 4%–6%]), epidural/subdural hematoma of the posterior cranial fossa (range 1%–2%), hydrocephalus and respiratory dysfunction (median 2%; IQR 1%–2% each), and postoperative headaches (in 9% of cases in 1 series). Of 60 series reporting complications, 22 (37%) were pediatric, 12 (20%) were adult, and 26 (43%) were combined (Fig. 12‌).

FIG. 12.
FIG. 12.

Distribution of reporting complications in the CM-I series.

In the pediatric series, complications were reported in 22 of 39 studies (56%), with a median of 3.5% (IQR 2.3%–14.3%). The complications most commonly reported were pseudomeningocele (range 5%–47% [median 15%; IQR 4.5%–18%]), aseptic meningitis (range 1%–60% [median 6%; IQR 3%–21%]), CSF leak (range 0.2%–21% [median 4%; IQR 3%–10.5%]), wound infection (range 1%–9% [median 3%; IQR 1%–4%]), meningitis (range 2%–4% [median 2%; IQR 2%–3%]), neurological deficit (range 1%–4% [median 2%; IQR 1%–3%]), epidural/subdural hematoma of the posterior cranial fossa (range 1%–2%), and hydrocephalus and respiratory insufficiency in 2% each. In 9% of the cases in 1 series, postoperative headaches were reported as a complication.

Postoperative complications in 12 of the adult studies were noted, with a median of 3% (IQR, 2.5%–5.5%). The most common were pseudomeningocele (range 1%–40% [median 2.5%; IQR 1.8%–12%]), aseptic meningitis (range 2%–4% [median 3%; IQR 2.5%–3.5%]), CSF leak (range 2%–11% [median 3%; IQR 1%–5%]), and meningitis (range 1%–4% [median 3%; IQR 2%–3.5%]) (Fig. 13‌).

FIG. 13.
FIG. 13.

Postoperative complications of CM-I; the distribution of the medians is stratified according to series.

The combined adult/pediatric series reported complications in 26 (60%) of 43 studies, with a median of 3% (IQR 1.3%–3.8%). The most common complications were CSF leakage (range 1%–24% [median 6%; IQR 5%–13%]), pseudomeningocele (range 1%–23% [median 12%; IQR 5%–18%]), aseptic meningitis (range 1%–33% [median 7%; IQR 4%–11%]), wound infection (range 2%–11% [median 3%; IQR 2%–7%]), meningitis (range 3%–9% [median 7%; IQR 5%–8%]), neurological deficit (range 1%–8% [median 4%; IQR 4%–5%]), epidural hematoma of the posterior cranial fossa (1%), trigeminal neuralgia (3%), intraventricular bleeding (3%), respiratory dysfunction (1%), and embolization (2%).

Mortality

Sixteen studies (11%) reported mortality-related data.2‌,8‌,11‌,17‌,23‌,26‌,32‌,58‌,70‌,90‌,95‌,96‌,102‌,117‌,140‌,159‌ Mortality was reported for 2 of 65 (3%) pediatric patients (years of study publication 1994 and 2010). Mortality was reported for 3 of 204 adult patients (2%) (years of study publication 1974–1977) and for 30 of 990 patients (3%) in the combined series (years of study publication 1968–2008). There was obviously no difference in the mortality rates between the adult and pediatric studies. The most commonly reported etiologies were pneumonia/respiratory failure (9 patients), infection/sepsis (7 patients), postoperative bleeding (3 patients), and sleep apnea (2 patients), whereas the rest of the etiologies were unknown or unclear.

Discussion

Chiari malformation Type I is a fairly common condition in the general population, ranging from 0.5% to 3.5% in general, from 0.56% to 0.77% in MRI, and 0.62% in anatomical brain-dissection studies.20‌,98‌,99‌ Among patients with CM-I, associated syringomyelia is frequent and has been reported to range from 30% to 70%.90‌,98‌,99‌,127‌ Between 15% and 30% of adult patients with CM-I are reportedly asymptomatic.20

Suboccipital craniectomy and foramen magnum decompression, with or without dural opening and with or without arachnoid opening and dissection, have been used most commonly for operative treatment; however, there is no clear idea of the frequency of their use in the reported series or whether a difference exists between pediatric and adult patients. Other unknowns are the precise geographic and continental distributions of reports of this malformation, sex and age demographics, lengths of follow-up, study durations, neurological outcomes, syrinx and headache improvement outcomes, rate and scope of complications, mortality, and whether differences exist between pediatric and adult populations with this malformation.

We encounter fairly large numbers of adult and pediatric patients with CM-I in our practice. Symptomatic patients and their families regularly ask precise questions regarding the expected success of their prospective operative treatment, the chances for improvement of their neurological deficits and syringomyelia, headaches, and the risks of potential complications. Furthermore, surgeons may benefit from comparing to their own patients the published demographics, operation types, outcomes, and complications in these patients. Our residents and members of other medical specialties who participate in the care of patients with CM-I frequently ask questions about various aspects of demographics, treatments, and outcomes. Finally, while preparing publications and presentations about various aspects of CM-I, many precise data are not available. These multiple reasons prompted this extensive review to provide all needed data in a single publication. To our knowledge, there has not been conducted thus far such an extensive and thorough review of operative CM-I series in the literature.

We identified 145 operative series of CM-I over the past 48 years (1965–2013).1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ Most of these publications (76%) were published in the past 21 years, with a clear increase in the frequency of publications in recent years. Thus, the results presented herein are fairly contemporary and present, in a broad sense, the current state of the art of operative treatment (Fig. 2‌). This increased frequency of reporting clearly coincides with the development and advancement of MRI techniques. The use of this diagnostic modality has undoubtedly contributed to the earlier and more accurate diagnosis of this condition and its severity, easier and more precise clinical follow-up of patients who are treated operatively and nonoperatively, improvements in the understanding of CM-I pathophysiology, refinement of operative treatments and outcomes, and an understanding of postoperative complications and the possibilities for preventing them.

Study Limitations

This review article analyzes the reported case series of patients with CM-I containing mostly Class III and, in rare cases, Class II evidence. This analysis was based on operative CM-I series only and did not include nonoperative series. These series have been published at different times, in different scientific journals, and from different countries. Non–English language literature on the subject was not included. As such, our study bears a number of limitations pertaining to these facts. While considering the strength of the information presented in this review (mostly Class III), the above facts should be taken in consideration.

Geographics

Almost half of the publications (46%) dealing with CM-I operative treatment for CM-I were published from the United States, and the majority of the other half came from the European Union (33%). The remaining reports originated from the rest of the world. It was surprising that Australia and Africa (Egypt) had only 1 publication each (Figs. 3‌ and 4‌). It is quite improbable that there is an increased incidence of CM-I in North America and Europe compared with that in the rest of world, and the reason for the disparity of reports from these and other regions is probably multifactorial. Some of the likely factors are as follows: a higher socioeconomic status and subsequent higher level of health care in North America and Europe, with an increased ratio of physicians, neurologists, and neurosurgeons to the population; a larger number of MRI facilities in North America and Europe; and a greater number of medical journals in North America and Europe available to publish reports. An increased incidence of patients with CM-I having a higher body mass index (BMI) and the influence of BMI on the formation of syringomyelia was elaborated recently.10‌ Therefore, one may speculate that a higher BMI is more common in wealthier nations. Furthermore, there is the question of whether a higher average age of the population in certain regions plays a role in the higher incidence of CM-I. Racial and ethnic differences may also play a role. In addition, medicolegal ramifications may influence the frequency with which studies are ordered; thus, more symptomatic patients may be discovered.

Study Durations, Patient Numbers, and Lengths of Follow-Up

The median number of patients per series was 31 (range 4–585). The mean study duration was 10 years (IQR 4–12 years), but it was somewhat shorter for adult patients (8 years). The mean follow-up time of all the patients was 43 months (slightly more than 3.5 years), but it was longer in adult series (46 months) than in the pediatric and combined series (37 and 39 months, respectively).1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ The distribution of follow-up times was asymmetrical, with median follow-up time shorter that the mean, showing that most of the studies had shorter follow-up times.

These findings suggest that, on average, investigators needed a relatively long period of time for the study (10 years), a moderately long mean follow-up time (3.5 years), and a moderate number of patients (31 cases) to accrue enough data for an individual study publication. These findings also point to the fact that, after surgery, most patients (adult and pediatric) are released from care after a maximum of 3.5 years (even less in some series) and that, for most patients, a follow-up time longer than 3.5 years is not needed.

Age of Patients

The distribution of adult and pediatric series (Fig. 1‌) and the ages of the adult and pediatric patients (Fig. 5‌) show that the frequency of CM-I has been similar between these 2 groups, with pediatric patients having just slightly more instances of the malformation. Therefore, it seems that CM-I is not more common in any of the age groups. The mean and median ages in the pediatric patient population were both 8 years, whereas in the adult population, they were 41 years. The mean and median ages in the combined studies were 33 and 35 years, respectively. In all the studies, the overall mean and median ages were 27 and 36 years, respectively (Table 2‌). It is interesting to note that 2 peak ages of presentation were delineated for each population (i.e., pediatric and adult). The peak ages of presentation in the pediatric studies were 8 years, followed by 9 years (Fig. 7‌ upper). The peak ages of presentation in the adult series were 41 years (Fig. 7‌ lower), and this figure was reported earlier.64‌,90‌ However, the next peak age was 46 years, which is a new finding. These data may help physicians to keep focus on the diagnostics in symptomatic patients of corresponding ages.

Sex of Patients

We noted a statistical difference between the sexes of patients in the studies, with females (39%) predominating (57% women [adult series] and 28% girls [pediatric series]). One reason for this predominance might be that women, particularly in the adult population, present more commonly with headache syndrome, which in turn may prompt more frequent MRI diagnostics. Meadows et al.98‌ questioned whether the female predominance is the result of more frequent initial cerebellar ectopia or a faster progression of symptoms later in life. Our data indicate that both are probably true.

Incidence of Syringomyelia

Syringomyelia is a cavitary enlargement101‌ or cyst formation71‌ of the spinal cord. CM-I is the leading cause of syringomyelia, and its pathogenesis was initially established by 2 classic hypotheses of Gardner59‌ and Williams.152‌,153‌ Milhorat et al.101‌ did experimental work on syringomyelia and the central spinal canal. More recently, Heiss et al.71‌,72‌ and Oldfield et al.112‌ proposed new insights into the pathophysiology of syringomyelia and its implications for the diagnosis and treatment of CM-I. Obviously, the creation and enlargement of a syrinx may contribute to the transformation of asymptomatic to symptomatic CM-I. In addition, gaining weight has been proposed as one of the contributing factors for de novo syrinx creation and patients becoming symptomatic.10

The association of syringomyelia with CM-I has been reported to range from 30% to 70%64‌ and 37% to 75%.27‌,79‌,98‌,99‌,110‌,117‌ This review also demonstrates the exact association of syringomyelia with CM-I in operative series. Ranges were 20%–100% in the adult series, 12%–100% in the pediatric series, and 32%–100% in the combined series. In absolute numbers, the rates of association of syringomyelia with CM-I were 69% in adult patients, 40% in pediatric patients, 78% in patients in the combined series, and 65% overall. In other words, two-thirds of all patients with CM-I treated operatively had syringomyelia (Table 3‌, Fig. 8‌), a statistically significant difference in favor of syrinx presence versus absence in patients with CM-I. This is not a surprise, because a syrinx gradually develops over years in a patient with CM-I. This frequency of syringomyelia in the series of patients with CM-I treated operatively confirms the notion that the presence of a syrinx plays one of the most important roles in symptomatology, the severity of presentation, and indications for surgery in all patient populations. Furthermore, the data on the mean and median ages of presentation (27 and 36 years, respectively) found in all the series and the fact that syringomyelia is more common in adult than in pediatric patients support the fact that symptomatic CM-I presents relatively late in life and needs time to develop. This fact is particularly interesting considering congenital and embryological theories of the development of this disorder (Table 2‌).

Operative Techniques

Several review articles surveyed the treatment of syringomyelia and CM-I in pediatric practices,69‌,131‌ but we were not able to identify similar surveys of adult CM-I practices. These reports by Haroun et al.69‌ and Schijman and Steinbok131‌ acknowledged differences in the management of pediatric CM-I. One consensus among these reviews was that asymptomatic patients should be observed unless there is an associated syrinx, and that most patients with CM-I with scoliosis underwent decompression regardless of whether they had an associated syrinx. Suboccipital foramen magnum decompression was the standard surgical procedure used, with the majority of surgeons opening the dura and using a graft. In their reviews of pediatric CM-I publications, Durham and Fjeld-Olenec42‌ and Hankinson et al.68‌ reported that posterior fossa decompression and dural opening with duraplasty are associated with a lower risk of reoperation but a greater risk of CSF-related complications. Sindou and Gimbert136‌ compared their technique of dural opening with duraplasty and preservation of the arachnoid membrane with other reported techniques. A Japanese review examined the differences between orthopedic (posterior fossa decompression only) and neurosurgical (posterior fossa decompression with duraplasty) techniques of decompression. They reported that the neurosurgical approach was associated with better neurological and syrinx improvement outcomes.130

The main goal of surgery for CM-I was summarized by Batzdorf18‌ as follows: resolving craniospinal pressure dissociation, restoring subarachnoid spaces and the cisterna magna in the posterior cranial fossa, eliminating and reducing the syrinx, relieving compression of the brainstem, and relieving or eliminating symptoms and signs of CM-I. In our analysis of published operative CM-I series, we noted that all the combined series, 97% of the pediatric series, and 85% of the adult series reported the operative technique used for treatment, and almost all of them described the use of posterior fossa/foramen magnum decompression. Furthermore, the dura was opened in 95%, 81%, and 97% of the cases, respectively. In addition, opening of the arachnoid membrane and intra-arachnoid dissection were reported in 72% and 70% of the combined and adult series, respectively, but only 47% of the pediatric series. The reason for the lower frequency of arachnoid membrane opening in pediatric studies probably lies in the attempt of some authors to decrease the incidence of CSF-related complications (pseudomeningocele, CSF leak, and aseptic and bacterial meningitis). However, considering all the studies (Table 4‌), the majority of patients were treated with arachnoid opening/dissection. We may speculate that there were 2 reasons for this treatment choice. One is that there may have been an arachnoid membrane velum closing the Magendi foramen, and most surgeons opted to directly inspect and open this membrane as needed. The other reason may be that according to their experience, a majority of the surgeons correlated overall good results of CM-I treatment with adding the arachnoid opening/dissection.

Tonsillar resection was relatively common in the pediatric series. Almost half of the pediatric studies (43%) in which the arachnoid membrane was opened also included this treatment, whereas only about one-quarter of adult and combined studies in which the membrane was opened (23% and 24%, respectively) added tonsillar resection. The reason for the more frequent tonsillar resection in pediatric patients is unclear.

Shunting was rarely performed, but it was used most commonly in the combined series (32%). One may speculate that some authors historically did not achieve the desired results with syrinx resolution after surgical decompression alone and therefore added shunting for their patients. Only a small proportion of procedures involved bone decompression only, possibly because of the relatively recent advent of that procedure.

Overall, posterior fossa/foramen magnum decompression, dural opening with duraplasty, and arachnoid opening with dissection were the most commonly used procedures in the adult and combined series, and they were used in about half of the pediatric series. Tonsillar resection was relatively common in the pediatric series, whereas shunting was common in the combined series.

Postoperative Outcomes: Syringomyelia

It is well established that CM-I is the leading cause of syringomyelia and that the creation (and worsening) of syringomyelia is one of the main causes of neurological symptoms and deficits in these patients. The improvement or resolution of syringomyelia is one of the main goals of the surgical treatment of patients with CM-I.18‌,69‌,131‌ Improvement/resolution of syringomyelia was described in all of the reported series (pediatric, adult, combined, and total) for almost three-quarters of the patients (78%) (Fig. 8‌, Table 5‌), and there was no statistical difference in syrinx outcomes among any of the series subgroups.1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ This outcome suggests that the use of operative decompression techniques achieved appropriate treatment goals in the majority of the patients. It should be noted, however, that about one-quarter of the patients (22%) still did not experience improvement. Therefore, additional means to further improve syrinx outcomes in this patient subgroup should be investigated.

Postoperative Outcomes: Neurological Status

Preoperative neurological deficits improved or resolved in 73% of the adult series, 84% of pediatric series, 72% of combined series, and 75% for all series (Table 6‌, Fig. 10‌). These satisfactory neurological results in approximately three-quarters of all patients correspond with the similarly good improvement/resolution of syrinx.1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ Neurological improvement/resolution was better in the pediatric series, but the data did not reach statistical significance. However, the difference in the results of worsening neurological deficits in the follow-up period (7% vs 1%, adult vs pediatric, respectively) did reach statistical significance. We may speculate that this difference is because younger patients frequently responded better to surgical decompression.

Postoperative Outcomes: Headaches

Suboccipital headaches aggravated by the Valsalva maneuver are one of the highlighted symptoms in all patients with CM-I.1‌–9‌,11‌–17‌,19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ However, only 16% of these series reported postoperative headache outcomes. As the other aspects of postoperative results showed, the improvement or resolution of headaches was also good, occurring in 73% of adult patients, 88% of pediatric patients, and 81% in all patients (Fig. 11‌). Although good postoperative outcomes were shown in both adult and pediatric patients, the fact that the difference in improvement/resolution outcomes between pediatric and adult series did reach statistical significance further supports the hypothesis that pediatric patients have somewhat better clinical results after decompression. Nonetheless, these findings clearly and strongly support the indication for surgical decompression in patients of all ages who have incapacitating headaches as the sole symptom of CM-I.

Complications

Only 41% of the series reported complications,1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ which is an interesting phenomenon. The median complication rate was 4.5%. It is unclear whether patients in the remaining 59% of the series did not have complications or simply did not report them. Of all series that reported complications, the most common were from the combined studies, followed by the pediatric and adult studies (Fig. 12‌).

Of all the pediatric series,1‌–3‌,15‌,24‌,28‌,30‌–33‌,35‌,41‌,42‌,50‌,51‌,54‌,56‌,60‌,61‌,65‌,77‌,80‌,81‌,86‌,89‌,92‌,93‌,97‌,104‌,108‌,109‌,116‌,133‌,134‌,143‌,145‌,150‌,154‌,155‌ 56% reported complications, with a median complication rate of 3.5%. The most common complications were pseudomeningocele, aseptic meningitis, CSF leak, meningitis, and neurological deficits (Fig. 13‌). The adult series that reported complications had a median complication rate of 3%, with CSF leak, aseptic meningitis, meningitis, and pseudomeningocele being the most frequent (Fig. 12‌). Clearly, CSF-related complications dominate in both pediatric and adult patient populations.

Postoperative mortality was rarely reported (only 11% of all series; 3% in pediatric series, 2% in adult series, and 3% in combined series),1‌–9‌,11‌–19‌,21‌–63‌,65‌–67‌,70‌,71‌,73‌–97‌,100‌,102‌–111‌,113‌–130‌,132‌–135‌,137‌–151‌,154‌–159‌ and there was no difference in the rates between adult and pediatric patients. The most common etiologies, in descending order of frequency, were pneumonia/respiratory failure, infection/sepsis, postoperative bleeding, and sleep apnea. The years of the series that reported complications were across the spectrum of the studied time interval. One may only speculate whether other series had no postoperative mortality whatsoever or if some series did not report it.

Conclusions

We have reviewed published operative CM-I series from the past 48 years and noted some novel, more precise information and provided propositions for future reporting of CM-I series. We have noted the increase in publications of surgical CM-I series in the past 21 years in all age groups. Most commonly, these series were published in the United States and Europe. The mean study duration was 10 years, and the mean follow-up time was 3.5 years. The median number of patients in the studies was 31.

Chiari I malformation was evenly distributed in adult and pediatric patients and was more common in female adults and children. In all the studies, the mean age was 27 years, and the median was 36 years. The peak ages of presentation were 8 years, followed by 9 years, in the pediatric series and 41 years, followed by 46 years, in the adult operative series. Two-thirds of all the patients in the operative CM-I series harbored syringomyelia, and its presence was more common in adults. In the adult and combined series, posterior fossa/foramen magnum decompression, dural opening/duraplasty, and arachnoid opening/dissection were used overwhelmingly. In pediatric patients, the frequency of arachnoid preservation versus arachnoid opening/dissection was evenly split.

The results of surgical treatment for patients with CM-I were excellent in all aspects: 78% improvement/resolution of syringomyelia, 75% neurological status improvement/resolution, and 81% suboccipital headache improvement/resolution. Postoperative headache outcome improvements were better in pediatric patients. A worsening of neurological status was more common in adult patients. Postoperative complications in pediatric patients were more commonly reported. Mortality is rare, most commonly resulting from pneumonia/respiratory failure, infection, sepsis, postoperative bleeding, and sleep apnea. For future publications on the subject of CM-I, we propose that authors provide details of all cases for the purpose of comparison, especially regarding the exact technique used.

Acknowledgments

We thank Kristina Kralik for help with statistics, Julie Yamamoto for technical editing, and Andrew J. Gienapp for copyediting, preparation of the manuscript and figures for publishing, and publication assistance with this manuscript.

Author Contributions

Conception and design: KI Arnautovic, Splavski, Boop. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: all authors. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: KI Arnautovic. Statistical analysis: KI Arnautovic, Splavski, Boop. Administrative/technical/material support: all authors. Study supervision: KI Arnautovic, Splavski, Boop.

References

  • 1

    Aitken LALindan CESidney SGupta NBarkovich AJSorel M: Chiari type I malformation in a pediatric population. Pediatr Neurol 40:4494542009

  • 2

    Albert GWMenezes AHHansen DRGreenlee JDWeinstein SL: Chiari malformation Type I in children younger than age 6 years: presentation and surgical outcome. J Neurosurg Pediatr 5:5545612010

  • 3

    Alden TDOjemann JGPark TS: Surgical treatment of Chiari I malformation: indications and approaches. Neurosurg Focus 11:1E22001

  • 4

    Alfieri APinna G: Long-term results after posterior fossa decompression in syringomyelia with adult Chiari Type I malformation. J Neurosurg Spine 17:3813872012

  • 5

    Aliaga LHekman KEYassari RStraus DLuther GChen J: A novel scoring system for assessing Chiari malformation type I treatment outcomes. Neurosurgery 70:6566652012

  • 6

    Alzate JCKothbauer KFJallo GIEpstein FJ: Treatment of Chiari I malformation in patients with and without syringomyelia: a consecutive series of 66 cases. Neurosurg Focus 11:1E32001

  • 7

    Appleby AFoster JBHankinson JHudgson P: The diagnosis and management of the Chiari anomalies in adult life. Brain 91:1311401968

  • 8

    Archer CRHorenstein SSundaram M: The Arnold-Chiari malformation presenting in adult life. A report of thirteen cases and a review of the literature. J Chronic Dis 30:3693821977

  • 9

    Armonda RACitrin CMFoley KTEllenbogen RG: Quantitative cine-mode magnetic resonance imaging of Chiari I malformations: an analysis of cerebrospinal fluid dynamics. Neurosurgery 35:2142241994

  • 10

    Arnautovic KIMuzevic DSplavski BBoop FA: Association of increased body mass index with Chiari malformation Type I and syrinx formation in adults. J Neurosurg 119:105810672013

  • 11

    Arora PBehari SBanerji DChhabra DKJain VK: Factors influencing the outcome in symptomatic Chiari I malformation. Neurol India 52:4704742004

  • 12

    Arruda JACosta CMTella OI Jr: Results of the treatment of syringomyelia associated with Chiari malformation: analysis of 60 cases. Arq Neuropsiquiatr 62:2A2372442004

  • 13

    Asgari SEngelhorn TBschor MSandalcioglu IEStolke D: Surgical prognosis in hindbrain related syringomyelia. Acta Neurol Scand 107:12212003

  • 14

    Attal NParker FTadié MAghakani NBouhassira D: Effects of surgery on the sensory deficits of syringomyelia and predictors of outcome: a long term prospective study. J Neurol Neurosurg Psychiatry 75:102510302004

  • 15

    Attenello FJMcGirt MJGarcés-Ambrossi GLChaichana KLCarson BJallo GI: Suboccipital decompression for Chiari I malformation: outcome comparison of duraplasty with expanded polytetrafluoroethylene dural substitute versus pericranial autograft. Childs Nerv Syst 25:1831902009

  • 16

    Badie BMendoza DBatzdorf U: Posterior fossa volume and response to suboccipital decompression in patients with Chiari I malformation. Neurosurgery 37:2142181995

  • 17

    Banerji NKMillar JHD: Chiari malformation presenting in adult life. Its relationship to syringomyelia. Brain 97:1571681974

  • 18

    Batzdorf U: Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. J Neurosurg 68:7267301988

  • 19

    Batzdorf UMcArthur DLBentson JR: Surgical treatment of Chiari malformation with and without syringomyelia: experience with 177 adult patients. J Neurosurg 118:2322422013

  • 20

    Bejjani GK: Definition of the adult Chiari malformation: a brief historical overview. Neurosurg Focus 11:1E12001

  • 21

    Bidziński J: Late results of the surgical treatment of syringomyelia. Acta Neurochir Suppl (Wien) 43:29311988

  • 22

    Bindal AKDunsker SBTew JM Jr: Chiari I malformation: classification and management. Neurosurgery 37:106910741995

  • 23

    Blagodatsky MDLarionov SNAlexandrov YAVelm AI: Surgical treatment of Chiari I malformation with or without syringomyelia. Acta Neurochir (Wien) 141:9639681999

  • 24

    Bollo RJRiva-Cambrin JBrockmeyer MMBrockmeyer DL: Complex Chiari malformations in children: an analysis of preoperative risk factors for occipitocervical fusion. J Neurosurg Pediatr 10:1341412012

  • 25

    Brockmeyer DGollogly SSmith JT: Scoliosis associated with Chiari I malformation: the effect of suboccipital decompression on scoliosis curve progression: a preliminary study. Spine 28:Phila Pa 1976250525092003

  • 26

    Caetano de Barros MFarias WAtaíde LLins S: Basilar impression and Arnold-Chiari malformation. A study of 66 cases. J Neurol Neurosurg Psychiatry 31:5966051968

  • 27

    Cahan LDBentson JR: Considerations in the diagnosis and treatment of syringomyelia and the Chiari malformation. J Neurosurg 57:24311982

  • 28

    Caldarelli MNovegno FVassimi LRomani RTamburrini GDi Rocco C: The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation Type I: experience with a pediatric series. J Neurosurg 106:3 Suppl1871952007

  • 29

    Chauvet DCarpentier AGeorge B: Dura splitting decompression in Chiari type 1 malformation: clinical experience and radiological findings. Neurosurg Rev 32:4654702009

  • 30

    Chen JACoutin-Churchman PENuwer MRLazareff JA: Suboccipital craniotomy for Chiari I results in evoked potential conduction changes. Surg Neurol Int 3:1652012

  • 31

    Chou YCSarkar ROsuagwu FCLazareff JA: Suboccipital craniotomy in the surgical treatment of Chiari I malformation. Childs Nerv Syst 25:111111142009

  • 32

    Cristante LWestphal MHerrmann HD: Cranio-cervical decompression for Chiari I malformation. A retrospective evaluation of functional outcome with particular attention to the motor deficits. Acta Neurochir (Wien) 130:941001994

  • 33

    Dauser RCDiPietro MAVenes JL: Symptomatic Chiari I malformation in childhood: a report of 7 cases. Pediatr Neurosci 14:1841901988

  • 34

    Depreitere BVan Calenbergh Fvan Loon JGoffin JPlets C: Posterior fossa decompression in syringomyelia associated with a Chiari malformation: a retrospective analysis of 22 patients. Clin Neurol Neurosurg 102:91962000

  • 35

    Di X: Endoscopic suboccipital decompression on pediatric Chiari type I. Minim Invasive Neurosurg 52:1191252009

  • 36

    Di Lorenzo NPalma LPalatinsky EFortuna A: “Conservative” cranio-cervical decompression in the treatment of syringomyelia-Chiari I complex. A prospective study of 20 adult cases. Spine (Phila Pa 1976) 20:247924831995

  • 37

    Dones JDe Jesús OColen CBToledo MMDelgado M: Clinical outcomes in patients with Chiari I malformation: a review of 27 cases. Surg Neurol 60:1421482003

  • 38

    Dubey ASung WSShaya MPatwardhan RWillis BSmith D: Complications of posterior cranial fossa surgery—an institutional experience of 500 patients. Surg Neurol 72:3693752009

  • 39

    du Boulay GShah SHCurrie JCLogue V: The mechanism of hydromyelia in Chiari type 1 malformations. Br J Radiol 47:5795871974

  • 40

    Duddy MJWilliams B: Hindbrain migration after decompression for hindbrain hernia: a quantitative assessment using MRI. Br J Neurosurg 5:1411521991

  • 41

    Dure LSPercy AKCheek WRLaurent JP: Chiari type I malformation in children. J Pediatr 115:5735761989

  • 42

    Durham SRFjeld-Olenec K: Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation Type I in pediatric patients: a meta-analysis. J Neurosurg Pediatr 2:42492008

  • 43

    Dyste GNMenezes AHVanGilder JC: Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg 71:1591681989

  • 44

    Eisenstat DDBernstein MFleming JFVanderlinden RGSchutz H: Chiari malformation in adults: a review of 40 cases. Can J Neurol Sci 13:2212281986

  • 45

    El-Ghandour NMF: Long-term outcome of surgical management of adult Chiari I malformation. Neurosurg Rev 35:5375472012

  • 46

    Ellenbogen RGArmonda RAShaw DWWinn HR: Toward a rational treatment of Chiari I malformation and syringomyelia. Neurosurg Focus 8:3E62000

  • 47

    Emery ERedondo ARey A: Syringomyelia and Arnold Chiari in scoliosis initially classified as idiopathic: experience with 25 patients. Eur Spine J 6:1581621997

  • 48

    Erdogan ECansever TSecer HITemiz CSirin SKabatas S: The evaluation of surgical treatment options in the Chiari malformation Type I. Turk Neurosurg 20:3033132010

  • 49

    Ergün RAkdemir GGezici ARTezel KBeskonakli EErgüngör F: Surgical management of syringomyelia-Chiari complex. Eur Spine J 9:5535572000

  • 50

    Eule JMErickson MAO'Brien MFHandler M: Chiari I malformation associated with syringomyelia and scoliosis: a twenty-year review of surgical and nonsurgical treatment in a pediatric population. Spine (Phila Pa 1976) 27:145114552002

  • 51

    Feldstein NAChoudhri TF: Management of Chiari I malformations with holocord syringohydromyelia. Pediatr Neurosurg 31:1431491999

  • 52

    Fischer EG: Posterior fossa decompression for Chiari I deformity, including resection of the cerebellar tonsils. Childs Nerv Syst 11:6256291995

  • 53

    Flynn JMSodha SLou JEAdams SB JrWhitfield BEcker ML: Predictors of progression of scoliosis after decompression of an Arnold Chiari I malformation. Spine (Phila Pa 1976) 29:2862922004

  • 54

    Foreman PSafavi-Abbasi STalley MCBoeckman LMapstone TB: Perioperative outcomes and complications associated with allogeneic duraplasty for the management of Chiari malformations Type I in 48 pediatric patients. J Neurosurg Pediatr 10:1421492012

  • 55

    Fujii KNatori YNakagaki HFukui M: Management of syringomyelia associated with Chiari malformation: comparative study of syrinx size and symptoms by magnetic resonance imaging. Surg Neurol 36:2812851991

  • 56

    Galarza MSood SHam S: Relevance of surgical strategies for the management of pediatric Chiari type I malformation. Childs Nerv Syst 23:6916962007

  • 57

    Gambardella GCaruso GCaffo MGermanò ALa Rosa GTomasello F: Transverse microincisions of the outer layer of the dura mater combined with foramen magnum decompression as treatment for syringomyelia with Chiari I malformation. Acta Neurochir (Wien) 140:1341391998

  • 58

    Garcìa-Uria JLeunda GCarrillo RBravo G: Syringomyelia: long-term results after posterior fossa decompression. J Neurosurg 54:3803831981

  • 59

    Gardner WJ: Hydrodynamic mechanism of syringomyelia: its relationship to myelocele. J Neurol Neurosurg Psychiatry 28:2472591965

  • 60

    Genitori LPeretta PNurisso CMacinante LMussa F: Chiari type I anomalies in children and adolescents: minimally invasive management in a series of 53 cases. Childs Nerv Syst 16:7077182000

  • 61

    Ghanem IBLondono CDelalande ODubousset JF: Chiari I malformation associated with syringomyelia and scoliosis. Spine (Phila Pa 1976) 22:131313181997

  • 62

    Godil SSParker SLZuckerman SLMendenhall SKMcGirt MJ: Accurately measuring outcomes after surgery for adult Chiari I malformation: determining the most valid and responsive instruments. Neurosurgery 72:8208272013

  • 63

    Goel ABhatjiwale MDesai K: Basilar invagination: a study based on 190 surgically treated patients. J Neurosurg 88:9629681998

  • 64

    Greenberg MS: Handbook of Neurosurgery ed 7New YorkThieme2010. 234

  • 65

    Greenlee JDDonovan KAHasan DMMenezes AH: Chiari I malformation in the very young child: the spectrum of presentations and experience in 31 children under age 6 years. Pediatrics 110:121212192002

  • 66

    Guo FWang MLong JWang HSun HYang B: Surgical management of Chiari malformation: analysis of 128 cases. Pediatr Neurosurg 43:3753812007

  • 67

    Guyotat JBret PJouanneau ERicci ACLapras C: Syringomyelia associated with type I Chiari malformation. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection. Acta Neurochir (Wien) 140:7457541998

  • 68

    Hankinson TTubbs RSWellons JC: Duraplasty or not? An evidence-based review of the pediatric Chiari I malformation. Childs Nerv Syst 27:35402011

  • 69

    Haroun RIGuarnieri MMeadow JJKraut MCarson BS: Current opinions for the treatment of syringomyelia and chiari malformations: survey of the Pediatric Section of the American Association of Neurological Surgeons. Pediatr Neurosurg 33:3113172000

  • 70

    Hayhurst CRichards OZaki HFindlay GPigott TJ: Hindbrain decompression for Chiari-syringomyelia complex: an outcome analysis comparing surgical techniques. Br J Neurosurg 22:86912008

  • 71

    Heiss JDPatronas NDeVroom HLShawker TEnnis RKammerer W: Elucidating the pathophysiology of syringomyelia. J Neurosurg 91:5535621999

  • 72

    Heiss JDSnyder KPeterson MMPatronas NJButman JASmith RK: Pathophysiology of primary spinal syringomyelia. J Neurosurg Spine 17:3673802012

  • 73

    Heiss JDSuffredini GBakhtian KDSarntinoranont MOldfield EH: Normalization of hindbrain morphology after decompression of Chiari malformation Type I. J Neurosurg 117:9429462012

  • 74

    Heller JBLazareff JGabbay JSLam SKawamoto HKBradley JP: Posterior cranial fossa box expansion leads to resolution of symptomatic cerebellar ptosis following Chiari I malformation repair. J Craniofac Surg 18:2742802007

  • 75

    Hida KIwasaki YKoyanagi ISawamura YAbe H: Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery 37:6736791995

  • 76

    Hoffman CESouweidane MM: Cerebrospinal fluid-related complications with autologous duraplasty and arachnoid sparing in type I Chiari malformation. Neurosurgery 62:3 Suppl 11561612008

  • 77

    Hoffman HJNeill JCrone KRHendrick EBHumphreys RP: Hydrosyringomyelia and its management in childhood. Neurosurgery 21:3473511987

  • 78

    Holly LTBatzdorf U: Management of cerebellar ptosis following craniovertebral decompression for Chiari I malformation. J Neurosurg 94:21262001

  • 79

    Isu TSasaki HTakamura HKobayashi N: Foramen magnum decompression with removal of the outer layer of the dura as treatment for syringomyelia occurring with Chiari I malformation. Neurosurgery 33:8458501993

  • 80

    James HEBrant A: Treatment of the Chiari malformation with bone decompression without durotomy in children and young adults. Childs Nerv Syst 18:2022062002

  • 81

    Jones RFAyer JGStening WA: Hydromyelia and Chiari malformation in children and adolescents. J Clin Neurosci 3:34451996

  • 82

    Klekamp J: Surgical treatment of Chiari I malformation—analysis of intraoperative findings, complications, and outcome for 371 foramen magnum decompressions. Neurosurgery 71:3653802012

  • 83

    Klekamp JBatzdorf USamii MBothe HW: The surgical treatment of Chiari I malformation. Acta Neurochir (Wien) 138:7888011996

  • 84

    Koç KAnik YAnik ICabuk BCeylan S: Chiari 1 malformation with syringomyelia: correlation of phase-contrast cine MR imaging and outcome. Turk Neurosurg 17:1831922007

  • 85

    Kotil KTon TTari RSavas Y: Delamination technique together with longitudinal incisions for treatment of Chiari I/syringomyelia complex: a prospective clinical study. Cerebrospinal Fluid Res 6:12009

  • 86

    Krieger MDMcComb JGLevy ML: Toward a simpler surgical management of Chiari I malformation in a pediatric population. Pediatr Neurosurg 30:1131211999

  • 87

    Kunert PJanowski MZakrzewska AMarchel A: Comparision of results between two different techniques of cranio-cervical decompression in patients with Chiari I malformation. Neurol Neurochir Pol 43:3373452009

  • 88

    Lam FCKasper E: Augmented autologuos pericranium duraplasty in 100 posterior fossa surgeries—a retrospective case series. Neurosurgery 71:2 Suppl Operativeons302ons3072012

  • 89

    Lazareff JAGalarza MGravori TSpinks TJ: Tonsillectomy without craniectomy for the management of infantile Chiari I malformation. J Neurosurg 97:101810222002

  • 90

    Levy WJMason LHahn JF: Chiari malformation presenting in adults: a surgical experience in 127 cases. Neurosurgery 12:3773901983

  • 91

    Liebenberg WAGeorges HDemetriades AKHardwidge C: Does posterior fossa decompression improve oculomotor and vestibulo-ocular manifestations in Chiari 1 malformation?. Acta Neurochir (Wien) 147:123912402005

  • 92

    Limonadi FMSelden NR: Dura-splitting decompression of the craniocervical junction: reduced operative time, hospital stay, and cost with equivalent early outcome. J Neurosurg 101:2 Suppl1841882004

  • 93

    Litvack ZNLindsay RASelden NR: Dura splitting decompression for Chiari I malformation in pediatric patients: clinical outcomes, healthcare costs, and resource utilization. Neurosurgery 72:9229292013

  • 94

    Logue VEdwards MR: Syringomyelia and its surgical treatment—an analysis of 75 patients. J Neurol Neurosurg Psychiatry 44:2732841981

  • 95

    Maroun FBJacob JCMangan M: The Chiari malformation in adults. Can J Neurol Sci 2:1151201975

  • 96

    Matsumoto TSymon L: Surgical management of syringomyelia—current results. Surg Neurol 32:2582651989

  • 97

    McGirt MJAttenello FJDatoo GGathinji MAtiba AWeingart JD: Intraoperative ultrasonography as a guide to patient selection for duraplasty after suboccipital decompression in children with Chiari malformation Type I. J Neurosurg Pediatr 2:52572008

  • 98

    Meadows JGuarnieri MMiller KHaroun RKraut MCarson BS: Type I Chiari malformation: a review of the literature. Neurosurg Q 11:2202292001

  • 99

    Meadows JKraut MGuarnieri MHaroun RICarson BS: Asymptomatic Chiari Type I malformations identified on magnetic resonance imaging. J Neurosurg 92:9209262000

  • 100

    Menezes AH: Chiari I malformations and hydromyelia—complications. Pediatr Neurosurg 17:1461541991. 1992

  • 101

    Milhorat THJohnson WDMiller JIBergland RMHollenberg-Sher J: Surgical treatment of syringomyelia based on magnetic resonance imaging criteria. Neurosurgery 31:2312451992

  • 102

    Mohr PDStrang FASambrook MABoddie HG: The clinical and surgical feature in 40 patients with primary cerebellar ectopia (adult Chiari malformation). Q J Med 46:85961977

  • 103

    Morgan DWilliams B: Syringobulbia: a surgical appraisal. J Neurol Neurosurg Psychiatry 55:113211411992

  • 104

    Mottolese CSzathmari ASimon ERousselle CRicci-Franchi ACHermier M: Treatment of Chiari type I malformation in children: the experience of Lyon. Neurol Sci 32:Suppl 3S325S3302011

  • 105

    Mueller DOro JJ: Prospective analysis of self-perceived quality of life before and after posterior fossa decompression in 112 patients with Chiari malformation with or without syringomyelia. Neurosurg Focus 18:2ECP22005

  • 106

    Munshi IFrim DStine-Reyes RWeir BKHekmatpanah JBrown F: Effects of posterior fossa decompression with and without duraplasty on Chiari malformation-associated hydromyelia. Neurosurgery 46:138413902000

  • 107

    Mutchnick ISJanjua RMMoeller KMoriarty TM: Decompression of Chiari malformation with and without duraplasty: morbidity versus recurrence. J Neurosurg Pediatr 5:4744782010

  • 108

    Nagib MG: An approach to symptomatic children (ages 4–14 years) with Chiari type I malformation. Pediatr Neurosurg 21:31351994

  • 109

    Navarro ROlavarria GSeshadri RGonzales-Portillo GMcLone DGTomita T: Surgical results of posterior fossa decompression for patients with Chiari I malformation. Childs Nerv Syst 20:3493562004

  • 110

    Nohria VOakes WJ: Chiari I malformation: a review of 43 patients. Pediatr Neurosurg 16:2222271990. 1991

  • 111

    Noudel RGomis PSotoares GBazin APierot LPruvo JP: Posterior fossa volume increase after surgery for Chiari malformation Type I: a quantitative assessment using magnetic resonance imaging and correlations with the treatment response. J Neurosurg 115:6476582011

  • 112

    Oldfield EHMuraszko KShawker THPatronas NJ: Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. J Neurosurg 80:3151994

  • 113

    Ono AUeyama KOkada AEchigoya NYokoyama THarata S: Adult scoliosis in syringomyelia associated with Chiari I malformation. Spine (Phila Pa 1976) 27:E23E282002

  • 114

    Padovani RCavallo MGaist G: Surgical treatment of syringomyelia: favorable results with syringosubarachnoid shunting. Surg Neurol 32:1731801989

  • 115

    Park JKGleason PLMadsen JRGoumnerova LCScott RM: Presentation and management of Chiari I malformation in children. Pediatr Neurosurg 26:1901961997

  • 116

    Parker SRHarris PCummings TJGeorge TFuchs HGrant G: Complications following decompression of Chiari malformation Type I in children: dural graft or sealant?. J Neurosurg Pediatr 8:1771832011

  • 117

    Paul KSLye RHStrang FADutton J: Arnold-Chiari malformation. Review of 71 cases. J Neurosurg 58:1831871983

  • 118

    Perrini PBenedetto NTenenbaum RDi Lorenzo N: Extra-arachnoidal cranio-cervical decompression for syringomyelia associated with Chiari I malformation in adults: technique assessment. Acta Neurochir (Wien) 149:101510232007

  • 119

    Pillay PKAwad IALittle JRHahn JF: Symptomatic Chiari malformation in adults: a new classification based on magnetic resonance imaging with clinical and prognostic significance. Neurosurgery 28:6396451991

  • 120

    Pinna GAlessandrini FAlfieri ARossi MBricolo A: Cerebrospinal fluid flow dynamics study in Chiari I malformation: implications for syrinx formation. Neurosurg Focus 8:3E32000

  • 121

    Prat RGaleano I: Pain improvement in patients with syringomyelia and Chiari I malformation treated with suboccipital decompression and tonsillar coagulation. J Clin Neurosci 16:5315342009

  • 122

    Pritz MB: Surgical treatment of Chiari I malformation: simplified technique and clinical results. Skull Base 13:1731772003

  • 123

    Raftopoulos CSanchez AMatos CBalériaux DBank WOBrotchi J: Hydrosyringomyelia-Chiari I complex. Prospective evaluation of a modified foramen magnum decompression procedure: preliminary results. Surg Neurol 39:1631691993

  • 124

    Rhoton AL Jr: Microsurgery of Arnold-Chiari malformation in adults with and without hydromyelia. J Neurosurg 45:4734831976

  • 125

    Romero FRPereira CA: Suboccipital craniectomy with or without duraplasty: what is the best choice in patients with Chiari type 1 malformation?. Arq Neuropsiquiatr 68:6236262010

  • 126

    Rowlands ASgouros SWilliams B: Ocular manifestations of hindbrain-related syringomyelia and outcome following craniovertebral decompression. Eye (Lond) 14:8848882000

  • 127

    Saez RJOnofrio BMYanagihara T: Experience with Arnold-Chiari malformation, 1960 to 1970. J Neurosurg 45:4164221976

  • 128

    Sakamoto HNishikawa MHakuba AYasui TKitano SNakanishi N: Expansive suboccipital cranioplasty for the treatment of syringomyelia associated with Chiari malformation. Acta Neurochir (Wien) 141:9499611999

  • 129

    Sakas DEKorfias SIWayte SCBeale DJPapapetrou KPStranjalis GS: Chiari malformation: CSF flow dynamics in the craniocervical junction and syrinx. Acta Neurochir (Wien) 147:122312332005

  • 130

    Sakushima KHida KYabe ITsuboi SUehara RSasaki H: Different surgical treatment techniques used by neurosurgeons and orthopedists for syringomyelia caused by Chiari I malformation in Japan. J Neurosurg Spine 18:5885922013

  • 131

    Schijman ESteinbok P: International survey on the management of Chiari I malformation and syringomyelia. Childs Nerv Syst 20:3413482004

  • 132

    Schlesinger EBAntunes JLMichelsen WJLouis KM: Hydromyelia: clinical presentation and comparison of modalities of treatment. Neurosurgery 9:3563651981

  • 133

    Scott WWFearon JASwift DMSacco DJ: Suboccipital decompression during posterior cranial vault remodeling for selected cases of Chiari malformations associated with craniosynostosis. J Neurosurg Pediatr 12:1661702013

  • 134

    Sengupta DKDorgan JFindlay GF: Can hindbrain decompression for syringomyelia lead to regression of scoliosis?. Eur Spine J 9:1982012000

  • 135

    Sindou MChávez-Machuca JHashish H: Cranio-cervical decompression for Chiari type I-malformation, adding extreme lateral foramen magnum opening and expansile duroplasty with arachnoid preservation. Technique and long-term functional results in 44 consecutive adult cases—comparison with literature data. Acta Neurochir (Wien) 144:100510192002

  • 136

    Sindou MGimbert E: Decompression for Chiari type I-malformation (with or without syringomyelia) by extreme lateral foramen magnum opening and expansile duraplasty with arachnoid preservation: comparison with other technical modalities (literature review). Adv Tech Stand Neurosurg 34:851102009

  • 137

    Spena GBernucci CGarbossa DValfrè WVersari P: Clinical and radiological outcome of craniocervical osteodural decompression for Chiari I-associated syringomyelia. Neurosurg Rev 33:2973042010

  • 138

    Stevens JMServa WAKendall BEValentine ARPonsford JR: Chiari malformation in adults: relation of morphological aspects to clinical features and operative outcome. J Neurol Neurosurg Psychiatry 56:107210771993

  • 139

    Takayasu MTakagi THara MAnzai M: A simple technique for expansive suboccipital cranioplasty following foramen magnum decompression for the treatment of syringomyelia associated with Chiari I malformation. Neurosurg Rev 27:1731772004

  • 140

    Taricco MAMelo LR: Retrospective study of patients with Chiari: malformation submitted to surgical treatment. Arq Neuropsiquiatr 66:2A1841882008

  • 141

    Tognetti FCalbucci F: Syringomyelia: syringo-subarachnoid shunt versus posterior fossa decompression. Acta Neurochir (Wien) 123:1961971993

  • 142

    Tokuno HHakuba ASuzuki TNishimura S: Operative treatment of Chiari malformation with syringomyelia. Acta Neurochir Suppl (Wien) 43:22251988

  • 143

    Tubbs RSBeckman JNaftel RPChern JJWellons JC IIIRozzelle CJ: Institutional experience with 500 cases of surgically treated pediatric Chiari malformation Type I. J Neurosurg Pediatr 7:2482562011

  • 144

    Ur-Rahman NJamjoom ZA: Surgical management of Chiari malformation and syringomyelia: experience in 14 cases. Ann Saudi Med 11:4024101991

  • 145

    Valentini LVisintini SSaletti VChiapparini LEstienne MSolero CL: Treatment for Chiari 1 malformation (CIM): analysis of a pediatric surgical series. Neurol Sci 32:Suppl 3S321S3242011

  • 146

    Vanaclocha VSaiz-Sapena N: Duraplasty with freeze-dried cadaveric dura versus occipital pericranium for Chiari type I malformation: comparative study. Acta Neurochir (Wien) 139:1121191997

  • 147

    Vanaclocha VSaiz-Sapena NGarcia-Casasola MC: Surgical technique for cranio-cervical decompression in syringomyelia associated with Chiari type I malformation. Acta Neurochir (Wien) 139:5295401997

  • 148

    Vaquero JMartínez RArias A: Syringomyelia-Chiari complex: magnetic resonance imaging and clinical evaluation of surgical treatment. J Neurosurg 73:64681990

  • 149

    Versari PPD'Aliberti GTalamonti GCollice M: Foraminal syringomyelia: suggestion for a grading system. Acta Neurochir (Wien) 125:971041993

  • 150

    Weinberg JSFreed DLSadock JHandler MWisoff JHEpstein FJ: Headache and Chiari I malformation in the pediatric population. Pediatr Neurosurg 29:14181998

  • 151

    Wetjen NMHeiss JDOldfield EH: Time course of syringomyelia resolution following decompression of Chiari malformation Type I. J Neurosurg Pediatr 1:1181232008

  • 152

    Williams B: The distending force in the production of “communicating syringomyelia”. Lancet 2:1891931969

  • 153

    Williams B: On the pathogenesis of syringomyelia: a review. J R Soc Med 73:7988061980

  • 154

    Yarbrough CKPowers AKPark TSLeonard JRLimbrick DDSmyth MD: Patients with Chiari malformation Type I presenting with acute neurological deficits: case series. J Neurosurg Pediatr 7:2442472011

  • 155

    Yeh DDKoch BCrone KR: Intraoperative ultrasonography used to determine the extent of surgery necessary during posterior fossa decompression in children with Chiari I malformation Type I. J Neurosurg 105:1 Suppl26322006

  • 156

    Yilmaz AKanat AMusluman AMColak ITerzi YKayacı S: When is duraplasty required in the surgical treatment of Chiari malformation type I based on tonsillar descending grading scale?. World Neurosurg 75:3073132011

  • 157

    Zamel KGalloway GKosnik EJRaslan MAdeli A: Intraoperative neurophysiologic monitoring in 80 patients with Chiari I malformation: role of duraplasty. J Clin Neurophysiol 26:70752009

  • 158

    Zhang YZhang NQiu HZhou JLi PRen M: An efficacy analysis of posterior fossa decompression techniques in the treatment of Chiari malformation with associated syringomyelia. J Clin Neurosci 18:134613492011

  • 159

    Zhang ZQChen YQChen YAWu XWang YBLi XG: Chiari I malformation associated with syringomyelia: a retrospective study of 316 surgically treated patients. Spinal Cord 46:3583632008

If the inline PDF is not rendering correctly, you can download the PDF file here.

Article Information

Correspondence Kenan I. Arnautovic, 6325 Humphreys Blvd., Memphis, TN 38120. email: kenanarnaut@yahoo.com.

INCLUDE WHEN CITING Published online December 5, 2014; DOI: 10.3171/2014.10.PEDS14295.

DISCLOSURE The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Age distribution of patients in the CM-I operative series.

  • View in gallery

    Number of CM-I operative studies according to the year of publication.

  • View in gallery

    Number of operative CM-I studies according to the country of publication.

  • View in gallery

    Distribution of CM-I studies according to the continent of publication.

  • View in gallery

    Age distribution of patients with CM-I.

  • View in gallery

    Sex distribution of patients with CM-I.

  • View in gallery

    Upper: Scatter plot graph of the presentation ages of patients with CM-I in the pediatric series. Lower: Scatter plot graph of the presentation ages of patients in the adult series.

  • View in gallery

    Incidence of syringomyelia in patients in the CM-I operative series.

  • View in gallery

    Distribution of patients with CM-I according to syringomyelia outcome.

  • View in gallery

    Postoperative distribution of neurological status outcomes according to CM-I series.

  • View in gallery

    Postoperative headache outcomes according to CM-I series.

  • View in gallery

    Distribution of reporting complications in the CM-I series.

  • View in gallery

    Postoperative complications of CM-I; the distribution of the medians is stratified according to series.

References

1

Aitken LALindan CESidney SGupta NBarkovich AJSorel M: Chiari type I malformation in a pediatric population. Pediatr Neurol 40:4494542009

2

Albert GWMenezes AHHansen DRGreenlee JDWeinstein SL: Chiari malformation Type I in children younger than age 6 years: presentation and surgical outcome. J Neurosurg Pediatr 5:5545612010

3

Alden TDOjemann JGPark TS: Surgical treatment of Chiari I malformation: indications and approaches. Neurosurg Focus 11:1E22001

4

Alfieri APinna G: Long-term results after posterior fossa decompression in syringomyelia with adult Chiari Type I malformation. J Neurosurg Spine 17:3813872012

5

Aliaga LHekman KEYassari RStraus DLuther GChen J: A novel scoring system for assessing Chiari malformation type I treatment outcomes. Neurosurgery 70:6566652012

6

Alzate JCKothbauer KFJallo GIEpstein FJ: Treatment of Chiari I malformation in patients with and without syringomyelia: a consecutive series of 66 cases. Neurosurg Focus 11:1E32001

7

Appleby AFoster JBHankinson JHudgson P: The diagnosis and management of the Chiari anomalies in adult life. Brain 91:1311401968

8

Archer CRHorenstein SSundaram M: The Arnold-Chiari malformation presenting in adult life. A report of thirteen cases and a review of the literature. J Chronic Dis 30:3693821977

9

Armonda RACitrin CMFoley KTEllenbogen RG: Quantitative cine-mode magnetic resonance imaging of Chiari I malformations: an analysis of cerebrospinal fluid dynamics. Neurosurgery 35:2142241994

10

Arnautovic KIMuzevic DSplavski BBoop FA: Association of increased body mass index with Chiari malformation Type I and syrinx formation in adults. J Neurosurg 119:105810672013

11

Arora PBehari SBanerji DChhabra DKJain VK: Factors influencing the outcome in symptomatic Chiari I malformation. Neurol India 52:4704742004

12

Arruda JACosta CMTella OI Jr: Results of the treatment of syringomyelia associated with Chiari malformation: analysis of 60 cases. Arq Neuropsiquiatr 62:2A2372442004

13

Asgari SEngelhorn TBschor MSandalcioglu IEStolke D: Surgical prognosis in hindbrain related syringomyelia. Acta Neurol Scand 107:12212003

14

Attal NParker FTadié MAghakani NBouhassira D: Effects of surgery on the sensory deficits of syringomyelia and predictors of outcome: a long term prospective study. J Neurol Neurosurg Psychiatry 75:102510302004

15

Attenello FJMcGirt MJGarcés-Ambrossi GLChaichana KLCarson BJallo GI: Suboccipital decompression for Chiari I malformation: outcome comparison of duraplasty with expanded polytetrafluoroethylene dural substitute versus pericranial autograft. Childs Nerv Syst 25:1831902009

16

Badie BMendoza DBatzdorf U: Posterior fossa volume and response to suboccipital decompression in patients with Chiari I malformation. Neurosurgery 37:2142181995

17

Banerji NKMillar JHD: Chiari malformation presenting in adult life. Its relationship to syringomyelia. Brain 97:1571681974

18

Batzdorf U: Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. J Neurosurg 68:7267301988

19

Batzdorf UMcArthur DLBentson JR: Surgical treatment of Chiari malformation with and without syringomyelia: experience with 177 adult patients. J Neurosurg 118:2322422013

20

Bejjani GK: Definition of the adult Chiari malformation: a brief historical overview. Neurosurg Focus 11:1E12001

21

Bidziński J: Late results of the surgical treatment of syringomyelia. Acta Neurochir Suppl (Wien) 43:29311988

22

Bindal AKDunsker SBTew JM Jr: Chiari I malformation: classification and management. Neurosurgery 37:106910741995

23

Blagodatsky MDLarionov SNAlexandrov YAVelm AI: Surgical treatment of Chiari I malformation with or without syringomyelia. Acta Neurochir (Wien) 141:9639681999

24

Bollo RJRiva-Cambrin JBrockmeyer MMBrockmeyer DL: Complex Chiari malformations in children: an analysis of preoperative risk factors for occipitocervical fusion. J Neurosurg Pediatr 10:1341412012

25

Brockmeyer DGollogly SSmith JT: Scoliosis associated with Chiari I malformation: the effect of suboccipital decompression on scoliosis curve progression: a preliminary study. Spine 28:Phila Pa 1976250525092003

26

Caetano de Barros MFarias WAtaíde LLins S: Basilar impression and Arnold-Chiari malformation. A study of 66 cases. J Neurol Neurosurg Psychiatry 31:5966051968

27

Cahan LDBentson JR: Considerations in the diagnosis and treatment of syringomyelia and the Chiari malformation. J Neurosurg 57:24311982

28

Caldarelli MNovegno FVassimi LRomani RTamburrini GDi Rocco C: The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation Type I: experience with a pediatric series. J Neurosurg 106:3 Suppl1871952007

29

Chauvet DCarpentier AGeorge B: Dura splitting decompression in Chiari type 1 malformation: clinical experience and radiological findings. Neurosurg Rev 32:4654702009

30

Chen JACoutin-Churchman PENuwer MRLazareff JA: Suboccipital craniotomy for Chiari I results in evoked potential conduction changes. Surg Neurol Int 3:1652012

31

Chou YCSarkar ROsuagwu FCLazareff JA: Suboccipital craniotomy in the surgical treatment of Chiari I malformation. Childs Nerv Syst 25:111111142009

32

Cristante LWestphal MHerrmann HD: Cranio-cervical decompression for Chiari I malformation. A retrospective evaluation of functional outcome with particular attention to the motor deficits. Acta Neurochir (Wien) 130:941001994

33

Dauser RCDiPietro MAVenes JL: Symptomatic Chiari I malformation in childhood: a report of 7 cases. Pediatr Neurosci 14:1841901988

34

Depreitere BVan Calenbergh Fvan Loon JGoffin JPlets C: Posterior fossa decompression in syringomyelia associated with a Chiari malformation: a retrospective analysis of 22 patients. Clin Neurol Neurosurg 102:91962000

35

Di X: Endoscopic suboccipital decompression on pediatric Chiari type I. Minim Invasive Neurosurg 52:1191252009

36

Di Lorenzo NPalma LPalatinsky EFortuna A: “Conservative” cranio-cervical decompression in the treatment of syringomyelia-Chiari I complex. A prospective study of 20 adult cases. Spine (Phila Pa 1976) 20:247924831995

37

Dones JDe Jesús OColen CBToledo MMDelgado M: Clinical outcomes in patients with Chiari I malformation: a review of 27 cases. Surg Neurol 60:1421482003

38

Dubey ASung WSShaya MPatwardhan RWillis BSmith D: Complications of posterior cranial fossa surgery—an institutional experience of 500 patients. Surg Neurol 72:3693752009

39

du Boulay GShah SHCurrie JCLogue V: The mechanism of hydromyelia in Chiari type 1 malformations. Br J Radiol 47:5795871974

40

Duddy MJWilliams B: Hindbrain migration after decompression for hindbrain hernia: a quantitative assessment using MRI. Br J Neurosurg 5:1411521991

41

Dure LSPercy AKCheek WRLaurent JP: Chiari type I malformation in children. J Pediatr 115:5735761989

42

Durham SRFjeld-Olenec K: Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation Type I in pediatric patients: a meta-analysis. J Neurosurg Pediatr 2:42492008

43

Dyste GNMenezes AHVanGilder JC: Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg 71:1591681989

44

Eisenstat DDBernstein MFleming JFVanderlinden RGSchutz H: Chiari malformation in adults: a review of 40 cases. Can J Neurol Sci 13:2212281986

45

El-Ghandour NMF: Long-term outcome of surgical management of adult Chiari I malformation. Neurosurg Rev 35:5375472012

46

Ellenbogen RGArmonda RAShaw DWWinn HR: Toward a rational treatment of Chiari I malformation and syringomyelia. Neurosurg Focus 8:3E62000

47

Emery ERedondo ARey A: Syringomyelia and Arnold Chiari in scoliosis initially classified as idiopathic: experience with 25 patients. Eur Spine J 6:1581621997

48

Erdogan ECansever TSecer HITemiz CSirin SKabatas S: The evaluation of surgical treatment options in the Chiari malformation Type I. Turk Neurosurg 20:3033132010

49

Ergün RAkdemir GGezici ARTezel KBeskonakli EErgüngör F: Surgical management of syringomyelia-Chiari complex. Eur Spine J 9:5535572000

50

Eule JMErickson MAO'Brien MFHandler M: Chiari I malformation associated with syringomyelia and scoliosis: a twenty-year review of surgical and nonsurgical treatment in a pediatric population. Spine (Phila Pa 1976) 27:145114552002

51

Feldstein NAChoudhri TF: Management of Chiari I malformations with holocord syringohydromyelia. Pediatr Neurosurg 31:1431491999

52

Fischer EG: Posterior fossa decompression for Chiari I deformity, including resection of the cerebellar tonsils. Childs Nerv Syst 11:6256291995

53

Flynn JMSodha SLou JEAdams SB JrWhitfield BEcker ML: Predictors of progression of scoliosis after decompression of an Arnold Chiari I malformation. Spine (Phila Pa 1976) 29:2862922004

54

Foreman PSafavi-Abbasi STalley MCBoeckman LMapstone TB: Perioperative outcomes and complications associated with allogeneic duraplasty for the management of Chiari malformations Type I in 48 pediatric patients. J Neurosurg Pediatr 10:1421492012

55

Fujii KNatori YNakagaki HFukui M: Management of syringomyelia associated with Chiari malformation: comparative study of syrinx size and symptoms by magnetic resonance imaging. Surg Neurol 36:2812851991

56

Galarza MSood SHam S: Relevance of surgical strategies for the management of pediatric Chiari type I malformation. Childs Nerv Syst 23:6916962007

57

Gambardella GCaruso GCaffo MGermanò ALa Rosa GTomasello F: Transverse microincisions of the outer layer of the dura mater combined with foramen magnum decompression as treatment for syringomyelia with Chiari I malformation. Acta Neurochir (Wien) 140:1341391998

58

Garcìa-Uria JLeunda GCarrillo RBravo G: Syringomyelia: long-term results after posterior fossa decompression. J Neurosurg 54:3803831981

59

Gardner WJ: Hydrodynamic mechanism of syringomyelia: its relationship to myelocele. J Neurol Neurosurg Psychiatry 28:2472591965

60

Genitori LPeretta PNurisso CMacinante LMussa F: Chiari type I anomalies in children and adolescents: minimally invasive management in a series of 53 cases. Childs Nerv Syst 16:7077182000

61

Ghanem IBLondono CDelalande ODubousset JF: Chiari I malformation associated with syringomyelia and scoliosis. Spine (Phila Pa 1976) 22:131313181997

62

Godil SSParker SLZuckerman SLMendenhall SKMcGirt MJ: Accurately measuring outcomes after surgery for adult Chiari I malformation: determining the most valid and responsive instruments. Neurosurgery 72:8208272013

63

Goel ABhatjiwale MDesai K: Basilar invagination: a study based on 190 surgically treated patients. J Neurosurg 88:9629681998

64

Greenberg MS: Handbook of Neurosurgery ed 7New YorkThieme2010. 234

65

Greenlee JDDonovan KAHasan DMMenezes AH: Chiari I malformation in the very young child: the spectrum of presentations and experience in 31 children under age 6 years. Pediatrics 110:121212192002

66

Guo FWang MLong JWang HSun HYang B: Surgical management of Chiari malformation: analysis of 128 cases. Pediatr Neurosurg 43:3753812007

67

Guyotat JBret PJouanneau ERicci ACLapras C: Syringomyelia associated with type I Chiari malformation. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection. Acta Neurochir (Wien) 140:7457541998

68

Hankinson TTubbs RSWellons JC: Duraplasty or not? An evidence-based review of the pediatric Chiari I malformation. Childs Nerv Syst 27:35402011

69

Haroun RIGuarnieri MMeadow JJKraut MCarson BS: Current opinions for the treatment of syringomyelia and chiari malformations: survey of the Pediatric Section of the American Association of Neurological Surgeons. Pediatr Neurosurg 33:3113172000

70

Hayhurst CRichards OZaki HFindlay GPigott TJ: Hindbrain decompression for Chiari-syringomyelia complex: an outcome analysis comparing surgical techniques. Br J Neurosurg 22:86912008

71

Heiss JDPatronas NDeVroom HLShawker TEnnis RKammerer W: Elucidating the pathophysiology of syringomyelia. J Neurosurg 91:5535621999

72

Heiss JDSnyder KPeterson MMPatronas NJButman JASmith RK: Pathophysiology of primary spinal syringomyelia. J Neurosurg Spine 17:3673802012

73

Heiss JDSuffredini GBakhtian KDSarntinoranont MOldfield EH: Normalization of hindbrain morphology after decompression of Chiari malformation Type I. J Neurosurg 117:9429462012

74

Heller JBLazareff JGabbay JSLam SKawamoto HKBradley JP: Posterior cranial fossa box expansion leads to resolution of symptomatic cerebellar ptosis following Chiari I malformation repair. J Craniofac Surg 18:2742802007

75

Hida KIwasaki YKoyanagi ISawamura YAbe H: Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery 37:6736791995

76

Hoffman CESouweidane MM: Cerebrospinal fluid-related complications with autologous duraplasty and arachnoid sparing in type I Chiari malformation. Neurosurgery 62:3 Suppl 11561612008

77

Hoffman HJNeill JCrone KRHendrick EBHumphreys RP: Hydrosyringomyelia and its management in childhood. Neurosurgery 21:3473511987

78

Holly LTBatzdorf U: Management of cerebellar ptosis following craniovertebral decompression for Chiari I malformation. J Neurosurg 94:21262001

79

Isu TSasaki HTakamura HKobayashi N: Foramen magnum decompression with removal of the outer layer of the dura as treatment for syringomyelia occurring with Chiari I malformation. Neurosurgery 33:8458501993

80

James HEBrant A: Treatment of the Chiari malformation with bone decompression without durotomy in children and young adults. Childs Nerv Syst 18:2022062002

81

Jones RFAyer JGStening WA: Hydromyelia and Chiari malformation in children and adolescents. J Clin Neurosci 3:34451996

82

Klekamp J: Surgical treatment of Chiari I malformation—analysis of intraoperative findings, complications, and outcome for 371 foramen magnum decompressions. Neurosurgery 71:3653802012

83

Klekamp JBatzdorf USamii MBothe HW: The surgical treatment of Chiari I malformation. Acta Neurochir (Wien) 138:7888011996

84

Koç KAnik YAnik ICabuk BCeylan S: Chiari 1 malformation with syringomyelia: correlation of phase-contrast cine MR imaging and outcome. Turk Neurosurg 17:1831922007

85

Kotil KTon TTari RSavas Y: Delamination technique together with longitudinal incisions for treatment of Chiari I/syringomyelia complex: a prospective clinical study. Cerebrospinal Fluid Res 6:12009

86

Krieger MDMcComb JGLevy ML: Toward a simpler surgical management of Chiari I malformation in a pediatric population. Pediatr Neurosurg 30:1131211999

87

Kunert PJanowski MZakrzewska AMarchel A: Comparision of results between two different techniques of cranio-cervical decompression in patients with Chiari I malformation. Neurol Neurochir Pol 43:3373452009

88

Lam FCKasper E: Augmented autologuos pericranium duraplasty in 100 posterior fossa surgeries—a retrospective case series. Neurosurgery 71:2 Suppl Operativeons302ons3072012

89

Lazareff JAGalarza MGravori TSpinks TJ: Tonsillectomy without craniectomy for the management of infantile Chiari I malformation. J Neurosurg 97:101810222002

90

Levy WJMason LHahn JF: Chiari malformation presenting in adults: a surgical experience in 127 cases. Neurosurgery 12:3773901983

91

Liebenberg WAGeorges HDemetriades AKHardwidge C: Does posterior fossa decompression improve oculomotor and vestibulo-ocular manifestations in Chiari 1 malformation?. Acta Neurochir (Wien) 147:123912402005

92

Limonadi FMSelden NR: Dura-splitting decompression of the craniocervical junction: reduced operative time, hospital stay, and cost with equivalent early outcome. J Neurosurg 101:2 Suppl1841882004

93

Litvack ZNLindsay RASelden NR: Dura splitting decompression for Chiari I malformation in pediatric patients: clinical outcomes, healthcare costs, and resource utilization. Neurosurgery 72:9229292013

94

Logue VEdwards MR: Syringomyelia and its surgical treatment—an analysis of 75 patients. J Neurol Neurosurg Psychiatry 44:2732841981

95

Maroun FBJacob JCMangan M: The Chiari malformation in adults. Can J Neurol Sci 2:1151201975

96

Matsumoto TSymon L: Surgical management of syringomyelia—current results. Surg Neurol 32:2582651989

97

McGirt MJAttenello FJDatoo GGathinji MAtiba AWeingart JD: Intraoperative ultrasonography as a guide to patient selection for duraplasty after suboccipital decompression in children with Chiari malformation Type I. J Neurosurg Pediatr 2:52572008

98

Meadows JGuarnieri M