Clinical significance of imaging and histological characteristics of filum terminale in tethered cord syndrome

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Object

The pathophysiology of tethered cord syndrome (TCS) is uncertain; however, it has been suggested that fibrous and fatty elements within the filum terminale (FT) play a role. The objective of this study was to describe the radiological and histological features of the FT in TCS and determine if there are associations between those features and clinical outcomes, complications, and urodynamics.

Methods

In this retrospective study, histological, MRI, and clinical data obtained in 293 patients with TCS who underwent FT transection were reviewed and analyzed in a multivariate analysis.

Results

The median patient age was 4.9 years (range 0.3–64.3 years). On MRI, a fatty filum was present in 65% of patients and a thickened filum (> 2 mm) was seen in 45%. Histologically, the FT contained prominent fibrous tissue in 95%, nerve twigs in 79%, adipose tissue in 59%, and vascular tissue in 36%. Histological features associated with a thickened filum on MR images were adipose tissue (OR 3.5, p < 0.001), nerve twigs (OR 2.2, p = 0.028), and vascular tissue (OR 0.5, p = 0.025). Adipose tissue was associated with a conus level below the L2–3 disc space (OR 2.3, p = 0.031) and with a fatty filum on imaging (OR 9.8, p < 0.001). Nerve twigs were associated with abnormal urodynamics (OR 10.9, p = 0.049). The only variable predictive of clinical improvement was conus level; patients with conus levels caudal to L-2 were less likely to improve postoperatively (OR 0.3, p = 0.042).

Conclusions

Fibrous tissue was ubiquitous and may be important in the pathophysiology of TCS. Nerve twigs and adipose tissue were associated with abnormal urodynamics and low-lying coni, respectively. Although the majority of patients clinically improved, patients with normal conus levels had significantly better outcomes.

Abbreviations used in this paper:FT = filum terminale; TCS = tethered cord syndrome.

Abstract

Object

The pathophysiology of tethered cord syndrome (TCS) is uncertain; however, it has been suggested that fibrous and fatty elements within the filum terminale (FT) play a role. The objective of this study was to describe the radiological and histological features of the FT in TCS and determine if there are associations between those features and clinical outcomes, complications, and urodynamics.

Methods

In this retrospective study, histological, MRI, and clinical data obtained in 293 patients with TCS who underwent FT transection were reviewed and analyzed in a multivariate analysis.

Results

The median patient age was 4.9 years (range 0.3–64.3 years). On MRI, a fatty filum was present in 65% of patients and a thickened filum (> 2 mm) was seen in 45%. Histologically, the FT contained prominent fibrous tissue in 95%, nerve twigs in 79%, adipose tissue in 59%, and vascular tissue in 36%. Histological features associated with a thickened filum on MR images were adipose tissue (OR 3.5, p < 0.001), nerve twigs (OR 2.2, p = 0.028), and vascular tissue (OR 0.5, p = 0.025). Adipose tissue was associated with a conus level below the L2–3 disc space (OR 2.3, p = 0.031) and with a fatty filum on imaging (OR 9.8, p < 0.001). Nerve twigs were associated with abnormal urodynamics (OR 10.9, p = 0.049). The only variable predictive of clinical improvement was conus level; patients with conus levels caudal to L-2 were less likely to improve postoperatively (OR 0.3, p = 0.042).

Conclusions

Fibrous tissue was ubiquitous and may be important in the pathophysiology of TCS. Nerve twigs and adipose tissue were associated with abnormal urodynamics and low-lying coni, respectively. Although the majority of patients clinically improved, patients with normal conus levels had significantly better outcomes.

Although the true incidence of tethered cord syndrome (TCS) is unknown,2 it is estimated to be approximately 0.1% in primary school children.1 Although filum transection is one of the more common surgical interventions in pediatric neurosurgery, the pathophysiology of TCS is uncertain. A normal filum terminale (FT) is composed of glial fibers, peripheral nerves, blood vessels, fibrous connective tissue, adipose tissue, and ependymal cells.4,9 Tethered cord syndrome may be due to thickened or fatty structural elements within the FT2 that render it inappropriately tense, preventing normal stretching and movement as the spine flexes and extends. This mechanism would account for the pathophysiology of TCS due to a low-lying conus, in which FT tension had prevented normal spinal cord ascension during development. It could also explain the pathophysiology of TCS with an anatomically normal level conus but thickened or fibrous FT.2,13

In the absence of an obviously low-lying conus medullaris, a diagnosis of TCS can be challenging. Some authors cite the presence of an abnormally thickened filum greater than 2 mm in diameter17 or a fatty filum as indications of tethering.3 In many cases, the two are found together. However, not all patients with a fatty or thickened FT have symptomatic TCS. Findings of an anatomical tethered cord may be discovered after MRI is performed because of congenital abnormalities of the lumbosacral integument and gluteal fold, or occasionally after trauma.

The purpose of this retrospective study was to first determine the histological and radiological features common in TCS and then determine if an association exists between these features and clinical findings and outcomes in patients who have undergone a FT transection.

Methods

Study Design, Setting, Size, and Patient Population

This retrospective study was approved by the Oregon Health & Science University Institutional Review Board. The records of patients who underwent surgical transection of the FT (CPT code 63200) at Oregon Health & Science University from July 1, 2002, to July 1, 2011, were reviewed. Data collected included age, sex, clinical symptoms, urodynamics (if obtained), MRI characteristics (conus level, fatty filum defined as the presence of hyperintensity of the FT on T1-weighted MRI, and diameter of the FT), clinical improvement after filum transection, postoperative complications, and histological features (nerve twigs, fibrous tissue, vascular tissue, adipose tissue, and glial/ependymal tissue). Urodynamics were considered abnormal if one of the following was reported during evaluation by a pediatric urologist: detrusor instability or “neurogenic bladder” (decreased bladder compliance, hyperreflexia, and detrusorsphincter dyssynergy). Clinical improvement was defined as an improvement in the presenting symptom(s) by the patient or primary caregiver. Very young patients in whom symptoms could not be evaluated were excluded from this subanalysis. Patients with major spinal dysraphism such as diastematomyelia, myelomeningocele, and lipomyelomeningocele or tumors such as ependymoma and lipoma were excluded from the analysis. Patients were also excluded if they did not have MRI or histological data. Magnetic resonance imaging was performed at either 1.5 or 3 T. Histological specimens were reviewed by board-certified neuropathologists. If an individual characteristic (for example, vascular tissue) was omitted from the histological report, it was not included in statistical analysis. Elastic fibers were classified as fibrous tissue.

Surgical Technique

The top of the iliac crest was used to approximate the level of the L3–4 interspace. No fluoroscopy was used. In patients younger than 8 years of age, a laminoplasty of L-3 or L-4 was performed, whereas in the majority of adult patients, an interlaminar approach was used. Using microscopy, a very small midline durotomy was made, and the filum was isolated using a vessel loop. The rostral and caudal ends of an approximately 5 mm piece of filum were cauterized and then sharply transected. Neuromonitoring was not used.

Statistical Analysis

Stata (version 10.1, StataCorp LP) was used to perform multivariate analyses. Magnetic resonance imaging and histological variables, age, and sex (independent variables) were used to predict complications, abnormal urodynamics, and clinical outcome (dependent variables) in a multiple logistic regression analysis. Histological characteristics (independent variables) were also used to predict each MRI characteristic (dependent variables) in a multiple logistic regression analysis. A value of p < 0.05 was considered significant.

Results

Participants and Descriptive Data

A total of 293 consecutive patients met the study inclusion criteria of complete radiological and histological data. The median age was 4.9 years (range 0.3–64.3 years). One hundred sixty-five patients (56.3%) were female; 58 (25.6%) of 227 patients had documented urodynamic testing as part of their clinical evaluation. For 66 patients, it was not specified whether urodynamic testing was performed. The median age for the group of patients who had documented urodynamic testing was 7 years (range 0.8–62.3 years). Although selection criteria for obtaining urodynamic studies varied between the 3 pediatric and 5 adult neurosurgeons represented in this data set, common patient characteristics of those selected to undergo urodynamic testing were normal conus level and filum thickness; 45 (80.4%) of 56 had a conus level rostral to L2–3 and 37 (71.2%) of 52 had a normal filum diameter. Forty-one (70.1%) had abnormal urodynamic testing findings. There was an association between abnormal urodynamics and the presence of nerve twigs on histology of the FT (OR 10.9 [95% CI 1.0–117.5], p = 0.049).

One hundred ninety-eight patients (67.6%) presented with neurological, urological, and/or orthopedic signs and/or symptoms, while the remaining 95 patients (32.4%) had filum transection based on MRI and physical findings alone (generally on the lumbosacral examination), as they were too young to assess symptomatic complaints. All patients younger than 1 year presented with cutaneous abnormalities such as a sacral dimple or hemangioma, or obvious congenital anomalies such as imperforate anus or club feet. Selection criteria for surgery differed by the 3 neurosurgeons represented in this data subset, but typically included these signs in addition to an abnormal MR image demonstrating findings of cord tethering such as a low-lying conus, thickened filum, and/or fatty filum. The most common presenting symptoms were leg weakness or gait difficulty (n = 75), bowel and/or bladder symptoms (n = 68), back and/or leg pain (n = 53), and scoliosis (n = 19). Patients presenting only with voiding dysfunction with a normal level conus had abnormal urodynamics and were managed using medical and/or behavioral therapy by a board-certified urologist for at least 1 year prior to surgery.

One hundred fifty-two of the 198 symptomatic patients had complete follow-up records, and 138 (90.8%) of those were clinically improved at the most recent follow-up. The median age of those with symptomatic improvement was 5.4 years; however, on multivariate analysis, age was not associated with clinical improvement (p = 0.802). Ninety-five percent of patients presenting with bowel and/or bladder dysfunction, 91% of patients presenting with back and/or leg pain, and 88% of patients presenting with leg weakness and/or gait difficulty improved postoperatively. Conus level was the only variable associated with clinical improvement; patients with preoperative conus levels at L2–3 and caudal were less likely to improve clinically after filum transection (OR 0.3 [95% CI 0.1–1], p = 0.042).

Imaging and Histological Data

On MRI, a fatty filum was found in 187 (64.9%) of 288 patients and a thickened filum in 117 (44.8%) of 261 patients. Both a fatty and thickened filum were found in 99 (37.9%) of 261 patients and neither was found in 83 (31.8%) of 261 patients. The median conus level was L-2 (Fig. 1). A comparison of patients with conus levels rostral to L2–3 and conus levels at L2–3 and caudal is presented in Table 1.

Fig. 1.
Fig. 1.

Histogram showing the conus levels in all patients. The mean and median levels were L-2.

TABLE 1:

Comparison of patients with conus levels above and below L-2*

ParameterPatients w/ Conus Levels Rostral to L2–3Patients w/ Conus Levels at L2–3 & Caudal
no. of patients20184
median age in yrs (range)5 (0.3–58)3.2 (0.3–64.3)
histological characteristics
 nerve twigs155/194 (79.9)64/83 (77.1)
 fibrous tissue193/199 (97)76/84 (90.5)
 vascular tissue67/177 (37.9)25/75 (33.3)
 adipose tissue110/180 (61.1)45/80 (56.2)
 glial/ependymal tissue35/201 (17.4)22/84 (26.2)
imaging characteristics
 fatty filum131/201 (65.2)50/81 (61.7)
 thickened filum (>2 mm)77/185 (41.6)39/74 (52.7)
ParameterPatients w/ Conus Levels Rostral to L2–3Patients w/ Conus Levels at L2–3 & Caudal
no. of patients20184
median age in yrs (range)5 (0.3–58)3.2 (0.3–64.3)
histological characteristics
 nerve twigs155/194 (79.9)64/83 (77.1)
 fibrous tissue193/199 (97)76/84 (90.5)
 vascular tissue67/177 (37.9)25/75 (33.3)
 adipose tissue110/180 (61.1)45/80 (56.2)
 glial/ependymal tissue35/201 (17.4)22/84 (26.2)
imaging characteristics
 fatty filum131/201 (65.2)50/81 (61.7)
 thickened filum (>2 mm)77/185 (41.6)39/74 (52.7)

Values are presented as the number of patients (%) unless stated otherwise. Some individual radiographic and histological data are missing.

Eight patients are not included in the table because of missing conus level data.

Fibrous tissue was found in 275 (94.8%) of 290 histological specimens, nerve twigs in 223 (78.5%) of 284, adipose tissue in 157 (58.8%) of 267, vascular tissue in 93 (36%) of 259, and glial/ependymal tissue in 57 (19.5%) of 292 histological specimens (Fig. 2).

Fig. 2.
Fig. 2.

Photomicrographs of FT specimens. A: Normal FT specimen obtained from a patient undergoing dorsal rhizotomy. Note the presence of nerve twigs (a), vascular tissue (c), and a small amount of fibrous tissue (b). Bar = 100 μm. B: Specimen obtained from a patient who underwent filum transection for TCS. Note the prominence of adipose tissue (d). C: Specimen obtained from a patient who underwent filum transection for TCS. Note the prominence of fibrous tissue (b). Original magnification ×10, H & E.

Histological features associated with a thickened filum on MRI (> 2 mm) were adipose tissue (OR 3.5 [95% CI 2.0–6.3], p < 0.001), nerve twigs (OR 2.2 [95% CI 1.1–4.4], p = 0.028), and vascular tissue (OR 0.5 [95% CI 0.3–0.9], p = 0.025). Only adipose tissue (OR 2.3 [95% CI 1.1–5.1], p = 0.031) was associated with a conus level below the L2–3 disc space and with a fatty filum on MRI (OR 9.8 [95% CI 5.1–18.9], p < 0.001).

Other Analyses: Complications Associated With Surgical Intervention

Only 7 patients (2.4%) had complications as a result of surgery, including CSF leakage (n = 2, 0.7%), superficial infection requiring operative debridement (n = 2, 0.7%), pseudomeningocele (n = 1, 0.3%), superficial wound dehiscence managed nonoperatively (n = 1, 0.3%), and an episode of malignant hyperthermia associated with anesthetic agent (n = 1, 0.3%). On multiple logistic regression analysis, there were no variables significantly associated with complications. There was no instance of neurological injury, permanent complication of any kind, or death.

Discussion

In this retrospective study, nearly all patients with TCS had fibrous fila. This observation replicates that of 4 other much smaller histological studies of FT in patients with TCS.4,9,10,12 In a series of presumably normal FTs from 4 fetuses, none of the specimens had evidence of fibrosis.12 In another small series, normal FTs had thin collagen bundles and rare adipose tissue, whereas FTs from patients with urinary symptoms and hyperreflexive and hypertonic bladders on urodynamic testing had an increased amount of adipose connective and fibrous tissue.9 In a series of 6 fila of patients with TCS, histological features common in all specimens included adipose tissue, hyalinization, meningothelial proliferation, and fibrosis.12 Notably, those specimens were from patients with conus levels caudal to the L2–3 disc.12 In addition, our group previously found that patients with TCS without a thickened filum or low-lying conus on MRI had an FT composed primarily of dense fibrous tissue that was significantly more dense than that in 3 specimens from reference patients undergoing dorsal rhizotomy where the FT was composed of neurovascular bundles with minimal fibrous tissue.10

In this study, the presence of peripheral nerve twigs on histology was significantly associated with a thickened FT and abnormal urodynamic findings preoperatively. The FT develops from regression of the caudal cell mass.2,7 It is possible that a portion of the somatic and autonomic nerves destined to innervate the genitourinary system are “trapped” within an abnormal FT as the result of the disordered regression of the caudal cell mass that results in a tethered spinal cord. An alternative explanation is that these are nonfunctional coccygeal roots or other vestigial remnants. Indeed, several studies have shown significant improvement in urodynamic function following surgical transection of the FT, even with the conus at a normal level, implying that urological dysfunction in TCS may result from a combination of abnormal development and a tight filum causing ongoing tension on the conus medullaris.5,6,8,10,11

Although more than 90% of symptomatic patients improved following FT transection, those with higher preoperative conus levels had better clinical outcomes than those who did not. This finding has 2 possible explanations: either 1) patients with very low spinal cord termination may already suffer from more significant neurovascular injury to the conus medullaris14–16 and are less likely to improve regardless of intervention, or 2) many patients with a normal-positioned conus and symptoms suggestive of TCS may have clinically improved without intervention. In either case, this finding may have implications for surgical decision making and counseling of patients and their families regarding expectations for the outcomes of surgical intervention.

There is overlap in the histological architecture of normal and pathological FT specimens. In this study we did not quantify the amount of each studied histological feature. Instead, we noted the presence or absence of each characteristic as a prominent histological finding. Based on our results, it is likely that the relative amount of fibrous and adipose tissue in the FT is one factor influencing the occurrence of TCS. Whether adipose tissue is simply a marker of pathological formation of the FT, or actually contributes to abnormal tension that damages the spinal cord, is unknown. The presence of excessive fibrous tissue in the FT was almost universal in the patients studied here and is intuitively a likely source of pathological tension on the conus.

Study limitations include those implicit in any retrospective review. Although we found a significant association between abnormal urodynamics and nerve twigs, this result may be limited by the fact that only approximately 25% of all patients had documented urodynamic testing. Furthermore, the study, which focused on patients undergoing surgical filum transection, cannot comment on the implication of various urodynamic findings for prognosis after tethered cord release. Approximately one-third of the patients in the study were too young to report symptomatic complaints. Additionally, the youngest patients had not been toilet trained, and therefore the influence of filum transection on voiding function could not be directly assessed. Finally, as this series represents the patients of 8 different neurosurgeons, indications for surgery varied and surgical indications may have affected observed results of this study.

Histological specimens were reviewed by at least 1 of 4 different neuropathologists. Variability may exist in the histological reports, although reports noted the presence or absence of key tissues in their descriptions. This study was designed only to evaluate the presence or absence of key histological features of fila. Future studies may be directed at quantifying the amount of fibrous tissue, adipose tissue, vascular tissue, and nerve twigs and comparing these specimens with “normal” control fila. Additionally, MR images were acquired using several 1.5- and 3-T scanners, potentially confounding the imaging assessment of FT diameter and appearance.

Conclusions

In a large series of patients undergoing surgical filum transection for TCS, histological adipose tissue is associated with a thickened and fatty FT on MRI and low conus medullaris. Nerve twigs noted on histological examination are associated with abnormal findings on urodynamic testing, suggesting the presence of an error in caudal mass regression and differentiation. Although the majority of patients who underwent transection of the FT clinically improved, patients with a particularly low-lying conus medullaris preoperatively are less likely to experience improvement of their preexisting deficits and may be counseled accordingly.

Acknowledgments

We thank Shirley McCartney, Ph.D., for editorial assistance and Andy Rekito, M.S., for assistance with figures.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. An Oregon Health & Science University, Campagna Scholarship supported Mr. Strong.

Author contributions to the study and manuscript preparation include the following. Conception and design: Selden, Thompson. Acquisition of data: Thompson, Strong, Warren, Woltjer. Analysis and interpretation of data: Thompson, Strong, Warren. Drafting the article: Selden, Thompson, Strong, Warren. 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: Selden. Statistical analysis: Thompson.

This article contains some figures that are displayed in color online but in black-and-white in the print edition.

References

  • 1

    Bademci GSaygun MBatay FCakmak ABasar HAnbarci H: Prevalence of primary tethered cord syndrome associated with occult spinal dysraphism in primary school children in Turkey. Pediatr Neurosurg 42:4132006

  • 2

    Bui CJTubbs RSOakes WJ: Tethered cord syndrome in children: a review. Neurosurg Focus 23:2E22007

  • 3

    Bulsara KRZomorodi AREnterline DSGeorge TM: The value of magnetic resonance imaging in the evaluation of fatty filum terminale. Neurosurgery 54:3753802004

  • 4

    Choi BHKim RCSuzuki MChoe W: The ventriculus terminalis and filum terminale of the human spinal cord. Hum Pathol 23:9169201992

  • 5

    George TMCummings TJ: The immunohistochemical profile of the myelomeningocele placode: is the placode normal?. Pediatr Neurosurg 39:2342392003

  • 6

    Guerra LAPike JMilks JBarrowman NLeonard M: Outcome in patients who underwent tethered cord release for occult spinal dysraphism. J Urol 176:172917322006

  • 7

    Hertzler DA IIDePowell JJStevenson CBMangano FT: Tethered cord syndrome: a review of the literature from embryology to adult presentation. Neurosurg Focus 29:1E12010

  • 8

    Metcalfe PDLuerssen TGKing SJKaefer MMeldrum KKCain MP: Treatment of the occult tethered spinal cord for neuropathic bladder: results of sectioning the filum terminale. J Urol 176:182618302006

  • 9

    Selçuki MVatansever SInan SErdemli EBağdatoğlu CPolat A: Is a filum terminale with a normal appearance really normal?. Childs Nerv Syst 19:3102003

  • 10

    Selden NRNixon RRSkoog SRLashley DB: Minimal tethered cord syndrome associated with thickening of the terminal filum. J Neurosurg 105:3 Suppl2142182006

  • 11

    Steinbok PKariyattil RMacNeily AE: Comparison of section of filum terminale and non-neurosurgical management for urinary incontinence in patients with normal conus position and possible occult tethered cord syndrome. Neurosurgery 61:5505562007

  • 12

    Tehli OHodaj IKural CSolmaz IOnguru OIzci Y: A comparative study of histopathological analysis of filum terminale in patients with tethered cord syndrome and in normal human fetuses. Pediatr Neurosurg 47:4124162011

  • 13

    Wolf SSchneble FTröger J: The conus medullaris: time of ascendence to normal level. Pediatr Radiol 22:5905921992

  • 14

    Yamada SKnerium DSMandybur GMSchultz RLYamada BS: Pathophysiology of tethered cord syndrome and other complex factors. Neurol Res 26:7227262004

  • 15

    Yamada SSanders DCMaeda G: Oxidative metabolism during and following ischemia of cat spinal cord. Neurol Res 3:1161981

  • 16

    Yamada SZinke DESanders D: Pathophysiology of “tethered cord syndrome”. J Neurosurg 54:4945031981

  • 17

    Yundt KDPark TSKaufman BA: Normal diameter of filum terminale in children: in vivo measurement. Pediatr Neurosurg 27:2572591997

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Article Information

Address correspondence to: Nathan R. Selden, M.D., Ph.D., Department of Neurological Surgery, Oregon Health & Science University, 3303 SW Bond Ave., CH8N, Portland, OR 97239. email: seldenn@ohsu.edu.

Please include this information when citing this paper: published online January 3, 2014; DOI: 10.3171/2013.12.PEDS13370.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Histogram showing the conus levels in all patients. The mean and median levels were L-2.

  • View in gallery

    Photomicrographs of FT specimens. A: Normal FT specimen obtained from a patient undergoing dorsal rhizotomy. Note the presence of nerve twigs (a), vascular tissue (c), and a small amount of fibrous tissue (b). Bar = 100 μm. B: Specimen obtained from a patient who underwent filum transection for TCS. Note the prominence of adipose tissue (d). C: Specimen obtained from a patient who underwent filum transection for TCS. Note the prominence of fibrous tissue (b). Original magnification ×10, H & E.

References

1

Bademci GSaygun MBatay FCakmak ABasar HAnbarci H: Prevalence of primary tethered cord syndrome associated with occult spinal dysraphism in primary school children in Turkey. Pediatr Neurosurg 42:4132006

2

Bui CJTubbs RSOakes WJ: Tethered cord syndrome in children: a review. Neurosurg Focus 23:2E22007

3

Bulsara KRZomorodi AREnterline DSGeorge TM: The value of magnetic resonance imaging in the evaluation of fatty filum terminale. Neurosurgery 54:3753802004

4

Choi BHKim RCSuzuki MChoe W: The ventriculus terminalis and filum terminale of the human spinal cord. Hum Pathol 23:9169201992

5

George TMCummings TJ: The immunohistochemical profile of the myelomeningocele placode: is the placode normal?. Pediatr Neurosurg 39:2342392003

6

Guerra LAPike JMilks JBarrowman NLeonard M: Outcome in patients who underwent tethered cord release for occult spinal dysraphism. J Urol 176:172917322006

7

Hertzler DA IIDePowell JJStevenson CBMangano FT: Tethered cord syndrome: a review of the literature from embryology to adult presentation. Neurosurg Focus 29:1E12010

8

Metcalfe PDLuerssen TGKing SJKaefer MMeldrum KKCain MP: Treatment of the occult tethered spinal cord for neuropathic bladder: results of sectioning the filum terminale. J Urol 176:182618302006

9

Selçuki MVatansever SInan SErdemli EBağdatoğlu CPolat A: Is a filum terminale with a normal appearance really normal?. Childs Nerv Syst 19:3102003

10

Selden NRNixon RRSkoog SRLashley DB: Minimal tethered cord syndrome associated with thickening of the terminal filum. J Neurosurg 105:3 Suppl2142182006

11

Steinbok PKariyattil RMacNeily AE: Comparison of section of filum terminale and non-neurosurgical management for urinary incontinence in patients with normal conus position and possible occult tethered cord syndrome. Neurosurgery 61:5505562007

12

Tehli OHodaj IKural CSolmaz IOnguru OIzci Y: A comparative study of histopathological analysis of filum terminale in patients with tethered cord syndrome and in normal human fetuses. Pediatr Neurosurg 47:4124162011

13

Wolf SSchneble FTröger J: The conus medullaris: time of ascendence to normal level. Pediatr Radiol 22:5905921992

14

Yamada SKnerium DSMandybur GMSchultz RLYamada BS: Pathophysiology of tethered cord syndrome and other complex factors. Neurol Res 26:7227262004

15

Yamada SSanders DCMaeda G: Oxidative metabolism during and following ischemia of cat spinal cord. Neurol Res 3:1161981

16

Yamada SZinke DESanders D: Pathophysiology of “tethered cord syndrome”. J Neurosurg 54:4945031981

17

Yundt KDPark TSKaufman BA: Normal diameter of filum terminale in children: in vivo measurement. Pediatr Neurosurg 27:2572591997

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