Basilar invagination in osteogenesis imperfecta and related osteochondrodysplasias: medical and surgical management

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✓ Osteogenesis imperfecta (OI) is a heritable disorder of bone development caused by defective collagen synthesis. Basilar invagination is an uncommon but devastating complication of this disease. The authors present a comprehensive strategy for management of craniovertebral anomalies associated with OI and related osteochondrodysplasias.

Twenty-five patients with congenital osteochondrodysplasias (18 OI, four Hajdu—Cheney syndrome, and three spondyloepiphyseal dysplasia) and basilar invagination were evaluated between 1985 and 1995. The male/female ratio in this cohort was 1:1. The mean age at presentation was 11.9 years (range 13 months–20 years). Fourteen patients (56%) presented during adolescence (11–15 years of age). Symptoms and signs included headache (76%), lower cranial nerve dysfunction (68%), hyperreflexia (56%), quadriparesis (48%), ataxia (32%), nystagmus (28%), and scoliosis (20%). Four patients (16%) were asymptomatic. Seven (28%) had undergone previous posterior fossa decompression; one had also undergone ventral decompression. Imaging findings included basilar invagination (100%), ventral brainstem compression (84%), hydrocephalus (32%), hindbrain herniation (28%), and syringomyelia/syringobulbia (16%).

Patients with hydrocephalus underwent ventricular shunt placement. Reducible basilar invagination (40%) was treated with posterior fossa decompression and occipitocervical fusion. Those with irreducible ventral compression (60%) underwent transoral—transpalatopharyngeal decompression followed by occipitocervical fusion. All patients improved initially. However, basilar invagination progressed radiographically in 80% (symptomatic in 24%) despite successful fusion. Prolonged external orthotic immobilization with the modified Minerva brace afforded symptomatic improvement and arrested progression of the deformity. The mean follow-up period was 5.9 years (range 1.1–10.5 years).

Ventral brainstem compression in OI should be treated with ventral decompression, followed by occipitocervical fusion with contoured loop instrumentation to prevent further squamooccipital infolding. Despite fusion, however, basilar invagination tends to progress. Prolonged immobilization (particularly during adolescence) may stabilize symptoms and halt further invagination. This study represents the largest series to date addressing craniovertebral anomalies in OI and related congenital bone softening disorders.

Abstract

✓ Osteogenesis imperfecta (OI) is a heritable disorder of bone development caused by defective collagen synthesis. Basilar invagination is an uncommon but devastating complication of this disease. The authors present a comprehensive strategy for management of craniovertebral anomalies associated with OI and related osteochondrodysplasias.

Twenty-five patients with congenital osteochondrodysplasias (18 OI, four Hajdu—Cheney syndrome, and three spondyloepiphyseal dysplasia) and basilar invagination were evaluated between 1985 and 1995. The male/female ratio in this cohort was 1:1. The mean age at presentation was 11.9 years (range 13 months–20 years). Fourteen patients (56%) presented during adolescence (11–15 years of age). Symptoms and signs included headache (76%), lower cranial nerve dysfunction (68%), hyperreflexia (56%), quadriparesis (48%), ataxia (32%), nystagmus (28%), and scoliosis (20%). Four patients (16%) were asymptomatic. Seven (28%) had undergone previous posterior fossa decompression; one had also undergone ventral decompression. Imaging findings included basilar invagination (100%), ventral brainstem compression (84%), hydrocephalus (32%), hindbrain herniation (28%), and syringomyelia/syringobulbia (16%).

Patients with hydrocephalus underwent ventricular shunt placement. Reducible basilar invagination (40%) was treated with posterior fossa decompression and occipitocervical fusion. Those with irreducible ventral compression (60%) underwent transoral—transpalatopharyngeal decompression followed by occipitocervical fusion. All patients improved initially. However, basilar invagination progressed radiographically in 80% (symptomatic in 24%) despite successful fusion. Prolonged external orthotic immobilization with the modified Minerva brace afforded symptomatic improvement and arrested progression of the deformity. The mean follow-up period was 5.9 years (range 1.1–10.5 years).

Ventral brainstem compression in OI should be treated with ventral decompression, followed by occipitocervical fusion with contoured loop instrumentation to prevent further squamooccipital infolding. Despite fusion, however, basilar invagination tends to progress. Prolonged immobilization (particularly during adolescence) may stabilize symptoms and halt further invagination. This study represents the largest series to date addressing craniovertebral anomalies in OI and related congenital bone softening disorders.

The term osteogenesis imperfecta (OI) represents a heterogeneous group of heritable bone disorders characterized by extreme bone fragility and an innate inclination to fracture.13,43 Collectively, these disorders are relatively rare, with a composite incidence of approximately 6.5 per 100,000 live births, and a population prevalence of 1:30,000.36,41 In those so afflicted, involvement of the axial skeleton is common and is usually manifested by multiple thoracolumbar vertebral body compression fractures, kyphoscoliosis, and lumbosacral spondylolysis.51 Anomalies of the craniovertebral junction occur with less frequency, but may precipitate severe structural deformity and progressive neurological dysfunction when present. Of these anomalies, secondary basilar invagination may be the most common and disabling.2,5,8,9,11,15,17,18,22,30,34,37,38

Since Ekman's initial description of this condition as “congenital osteomalacia” in 1788, several taxonomic schemes have been proposed to categorize OI, including one by Weil.48 Looser23 divided OI into congenita and tarda forms, based on age at presentation. Subsequently, Sillence, et al.,42 proposed a four-tiered classification system that emphasized, in addition to age, the mode of inheritance and morphological findings (Table 1). Regardless of taxonomy, the hallmark of all forms of OI is bone fragility and osteopenia caused by defective type I collagen synthesis.7,13,43 Additional (but less consistent) clinical features characteristic of this disorder include blue sclerae, laxity of ligaments, presenile deafness, and impaired dentition.

TABLE 1

Taxonomy of OI according to Sillence, et al.

TypeVariantSubtypeClinical FeaturesInheritance
I dominant inheritedAvariable bone fragility; blueautosomal 
  OI sclerae; presenile hearing dominant 
  w/ blue loss/deafness; normal dentition; 
  sclerae presentation in adolescence 
  or early adulthood 
 BIA + dentinogenesis imperfecta 
II lethal perinatalsevere bone fragility; blueautosomal 
  OI sclerae; stillbirth or neonatal recessive, 
  death; crumpled/deformed or de novo 
  thin/beaded long bones & dominant 
  ribs mutations 
III progressivelyAprogressively deforming boneautosomal 
  deforming disease; normal sclerae (blue recessive 
  OI in infancy); severe spinal deformity; 
  skull deformity with 
  Wormian bones; marked ligamentous 
  laxity; normal dentition; 
  presentation in childhood 
 BIIIA + dentinogenesis imperfecta 
IV dominant inAvariable bone fragility (> typeautosomal 
  herited OI I); normal sclerae; moderate dominant 
  w/ normal spinal deformity; normal dentition; 
  sclerae variable age of presentation 
 BIVA + dentinogenesis imperfecta 

Other osteochondrodysplasias (heritable disorders of bone and cartilage development) may present with craniovertebral junction pathology that is indistinguishable from that associated with OI, based on clinical and radiological criteria. Among these, the spondyloepiphyseal dysplasias appear to be the most closely related to OI in terms of pathogenesis. This group of conditions arises from defects in type II collagen that are nearly identical to the type I collagen deficiencies present in some forms of OI.7,29 In both disorders, genetically programmed anomalies in collagen chain synthesis impair formation of the collagen triple helix, yielding structurally and functionally abnormal collagen in bone and other connective tissues.7,29 Another rare but morphologically similar condition that may affect the craniovertebral junction is the Hajdu—Cheney syndrome (known as “cranio-skeletal dysplasia”14 or “acro-osteolysis”6). Although the biochemical defect underlying this disorder remains obscure, some investigators have postulated that an impairment in collagen synthesis and maturation may precipitate dysplastic bone formation in this condition.6,49 Thus, it may be surmised that OI, spondyloepiphyseal dysplasia, and the Hajdu—Cheney syndrome, in addition to exhibiting similar clinical features, may share related pathogenic mechanisms.

Basilar invagination is a potentially devastating complication of OI and the related osteochondrodysplasias. Unfortunately, the rarity of these conditions and the relative infrequency of associated craniovertebral junction involvement has precluded the systematic study of the natural history of such lesions, as well as their response to treatment. However, based on the available literature we hypothesize the following: 1) the natural history of basilar invagination associated with these conditions is one of progressive deformity and neurological dysfunction, ending ultimately in the patient's death;5,15,17,20,22,30,32,34,37,38 2) posterior decompression alone (suboccipital craniectomy and upper cervical laminectomy) is inadequate treatment for this type of pathology and may actually hasten the progression of ventral brainstem compression;11,15,17,30,34 and 3) ventral decompression with subsequent dorsal fusion may be effective in ameliorating symptoms and halting progressive basilar invagination.15 The veracity of the last postulate is unclear, because published experience has been limited to single case reports or small series with generally short duration of follow up.

In this article, we review our experience with basilar invagination associated with OI and related osteochondrodysplasias and present a comprehensive strategy for medical and surgical management of the craniovertebral junction anomalies associated with these rare conditions.

Clinical Material and Methods

Between January 1985 and January 1995, 25 patients with OI or related congenital osteochondrodysplasias and secondary basilar invagination were evaluated by the senior author (A.H.M.) at the University of Iowa Hospitals and Clinics. Eighteen of these patients suffered from OI, and the majority of these (10 patients) exhibited the progressive deforming variant of OI (Sillence Type III). Six patients were subclassified with Type IV OI, and two with the Type I variant. The remaining seven patients were diagnosed with related congenital osteochondrodysplasias. Four of these patients exhibited the classic findings of the Hajdu—Cheney syndrome and three suffered from spondyloepiphyseal dysplasia. Patients with achondroplasia (including those with achondrogenesis, hypochondrogenesis, and thanatophoric dwarfism) represent a distinct clinical entity with respect to the craniovertebral junction and thus have been reported elsewhere.39

Clinical records, operative reports, and diagnostic studies for these 25 patients were reviewed to assess modes of presentation, radiographically recognized pathology, and response to treatment. All patients were evaluated with computerized tomography (CT) scanning and plain radiography prior to treatment; in most (18 patients) magnetic resonance (MR) images were also obtained as part of the initial diagnostic assessment.

Treatment was instituted prospectively according to the principles outlined in Fig. 1. Asymptomatic patients with basilar invagination were treated initially with external orthotic immobilization using a custom-modified Minerva-type brace (Fig. 2). Symptomatic patients with hydrocephalus underwent ventriculoperitoneal shunt placement as the initial intervention. Prior to decompressive surgery, patients underwent a trial of axial cervical traction, and those in whom basilar invagination was reducible with traction received posterior decompression (suboccipital craniectomy, rostral cervical laminectomy) and occipitocervical fusion with autogenous bone graft (with or without instrumentation). Irreducible invagination was treated with ventral decompression (transoral—transpalatopharyngeal, transmaxillary) followed by occipitocervical fusion.

Fig. 1.
Fig. 1.

Chart of algorithm outlining management strategy for patients with basilar invagination and OI or related osteochondrodysplasias.

Fig. 2.
Fig. 2.

Lateral (left) and posterior (right) views showing the custom-modified Minerva-type brace, worn by an 11-year-old girl with Hajdu—Cheney syndrome and basilar invagination.

Response to treatment was determined by annual clinical and radiological follow-up evaluations that included detailed neurological examination, CT and MR studies, and plain radiography. An assessment of functional status was made preoperatively and at each postoperative follow-up visit using a four-tiered grading system: 1) excellent, asymptomatic, normal neurological examination, independent in all activities; 2) good, minor symptoms/signs but able to participate in most activities and ambulate independently; 3) fair, some neurological disability, requires assistance with activities of daily living and ambulation; and 4) poor, severe impairment, requires constant nursing care, wheelchair bound. In patients who had undergone stabilization procedures, the integrity of the bone fusion was assessed by means of plain radiography (including flexion—extension views) and/or pluridirectional polytomography. Criteria for successful fusion included bone trabeculae traversing the graft—recipient interface, and long-term stability of the fused segments seen on flexion—extension radiographs. The mean follow-up period for the entire cohort was 5.9 years (range 1.1–10.5 years).

Results
Clinical, Demographic, and Radiological Data

The gender ratio in this series approached 1:1 (13 male/12 female). The mean age at presentation was 11.9 years (range 1–20 years). Fourteen patients (56%) presented within a 5-year time window between the ages of 11 and 15 years, rendering this portion of adolescence the most common age for presentation. Twenty-four patients were Caucasian; one was of Hispanic descent. Presenting symptoms and signs are summarized in Table 2; headache and dysphagia were the most frequently encountered presenting symptoms, and lower cranial nerve dysfunction, hyperreflexia, and quadriparesis were the most common abnormal neurological findings. Four patients (16%) were asymptomatic.

TABLE 2

Presenting symptoms and signs in 25 patients with basilar invagination and OI or related osteochondrodysplasias

Symptom/SignNo. of PatientsPercentage
headache1976
lower cranial nerve palsy*1768
dysphagia1560
hyperreflexia1456
quadriparesis1248
ataxia832
nystagmus728
thoracolumbar scoliosis520
hearing loss416

Includes cranial nerves IX, X, XI, and XII.

Seven patients (28%) had previously undergone surgical intervention at the craniovertebral junction prior to referral to our institution. Six patients (24%) had undergone posterior fossa decompression procedures, with occipitocervical fusion performed concomitantly in two of these patients. No fusion procedure had been attempted in the remaining four. An additional patient had undergone three previous ventral decompression procedures (two transoral—transpalatopharyngeal and one transmaxillary) followed by posterior fossa decompression and occipitocervical fusion with contoured loop instrumentation and an autogenous bone graft. Despite transient improvement or stabilization of symptoms after the initial surgical intervention in all cases, these previously treated patients experienced progressive basilar invagination and recurrence and/or exacerbation of neurological dysfunction. As a group, these patients were older (mean 14.6 years of age) and tended to present with clinical worsening during adolescence (86% between the ages of 11 and 15 years).

Data obtained from radiological investigations of the entire cohort are summarized in Table 3. The most characteristic abnormalities, aside from basilar invagination (present in all patients), were ventral brainstem compression, platybasia, and foreshortening of the clivus. Hydrocephalus was identified in eight patients, arising from compression of the sylvian aqueduct by the invaginating clivus-odontoid complex (Figs. 35). Thus, including the three patients who had undergone previous ventricular shunting prior to referral, the overall incidence of hydrocephalus in this population was 44%. Pseudoarthrosis was apparent on radiographic studies in two of the three patients who had undergone previous fusion procedures.

TABLE 3

Radiological imaging findings in 25 patients with OI or related osteochondrodysplasias*

FindingNo. of PatientsPercentage
basilar invagination25100
ventral brainstem compression2184
platybasia2080
foreshortening of the clivus1872
CVJ instability1248
CMJ encephalomyelomalacia936
hydrocephalus832
hindbrain herniation728
thoracolumbar scoliosis728
syringomyelia/syringobulbia416

CMJ = cervicomedullary junction; CVJ = craniovertebral junction.

Three additional patients had undergone previous ventricular shunting for hydrocephalus; thus, the overall incidence of hydrocephalus in this series was 44%.

Fig. 3.
Fig. 3.

Sagittal T1-weighted MR image demonstrating obstructive hydrocephalus from secondary aqueductal stenosis in a 19-year-old man with OI. Note the horizontally oriented clivus, rostrally displaced pontomedullary junction, and ventral brainstem compression from the invaginated clival-atlantoaxial complex.

Fig. 4.
Fig. 4.

Axial CT image obtained in a 13-year-old girl with spondyloepiphyseal dysplasia revealing invagination of the atlas and dens into the posterior fossa, with obstructive hydrocephalus and dilation of the lateral and third ventricles.

Fig. 5.
Fig. 5.

Coronal T1-weighted MR image obtained in a 12-year-old boy with Hajdu—Cheney syndrome demonstrating upward translocation of the upper cervical spine into the posterior fossa. Mild hydrocephalus is also evident.

Management Modalities

Treatment was undertaken according to the algorithm presented in Fig. 1. Asymptomatic cases (four patients) were initially treated conservatively, using external orthotic immobilization with a custom-modified Minerva brace. Of these four patients, three remain asymptomatic. The remaining individual became symptomatic (with headaches) despite bracing, thus requiring further surgical treatment, which we will outline.

Eight patients with symptomatic hydrocephalus underwent ventricular shunting as the initial therapeutic intervention. Two of these individuals experienced complete resolution of symptoms with shunting alone and, with subsequent immobilization in a custom-fitted orthotic device (modified Minerva brace), remain asymptomatic. Those who continued to experience symptoms despite resolution of hydrocephalus underwent further surgical intervention.

Twenty patients required surgical treatment to relieve neural compression. Prior to surgery, all patients underwent axial cervical traction in an effort to reduce ventral brainstem compression produced by the invaginating clivus—odontoid complex. Basilar invagination was reducible with inline cervical traction in eight patients (40% of surgically treated cases). In such instances, posterior fossa decompression was performed via suboccipital craniectomy, C-1 laminectomy, and duraplasty, followed by in situ occipitocervical fusion. Patients with irreducible ventral compression (60%) underwent ventral decompression (transoral—transpalatopharyngeal, transmaxillary) followed by dorsal occipitocervical stabilization. Regardless of the route(s) of decompression, fusion was performed in all cases using a construct consisting of either autogenous rib strut grafts and braided stainless steel/titanium sublaminar cables (six cases, earlier in the series) or contoured loop instrumentation (titanium or stainless steel) with autogenous bone grafts and braided sublaminar cables (14 cases). Postoperative immobilization was provided by halo vest (12 patients) or modified Minerva braces (eight patients) until a solid bone union was evident on follow-up radiographs. The mean duration of postoperative bracing was 8.2 months (range 6–13 months).

Postoperative Outcome

No surgically related deaths or major morbidity were incurred in this series. One patient required repositioning of a single halo crown pin because of a superficial pin-site infection. Aside from this, no difficulties were encountered with halo vest immobilization, despite the fragile nature of the calvarial bones in this patient population.

Functional status assessments are summarized in Table 4; all 21 symptomatic patients improved initially with treatment. At the peak of therapeutic benefit (“best posttreatment” status), 13 patients had improved by one grade (for example, from good to excellent or fair to good), and eight had improved by two grades. Three of the four initially asymptomatic patients remained so with prophylactic bracing; the remaining individual developed headaches despite bracing and required surgical decompression. All 20 patients who had undergone surgical stabilization demonstrated radiographic evidence of successful fusion, with a mean time to graft incorporation of 8.2 months (range 6–13 months).

TABLE 4

Assessment of functional status pre- and posttreatment in 25 patients with OI or related osteochondrodysplasias

No. of Cases
Grade*PretreatmentBest PosttreatmentFinal Posttreatment
excellent4129
good71113
fair1112
poor311

See Clinical Material and Methods for explanation of grades.

Despite successful bone fusion, however, basilar invagination showed progression according to imaging criteria in 20 (80%) of 25 patients. Of these, only six experienced symptomatic worsening, which consisted of recurrent headache and neck pain (in four patients), dysphagia (in one), and myelopathy (in one). Progressive invagination typically occurred during the period of rapid growth in adolescence (11–15 years of age). The incidence and degree of progression was similar in those treated with combined ventral/dorsal procedures and in those who underwent dorsal decompression and stabilization alone.

Progressive basilar invagination that occurred despite solid dorsal occipitocervical fixation was managed with prolonged external immobilization using a custom-modified Minerva brace. Patients were instructed to wear this orthotic device at all times except when recumbent, at which times a soft cervical collar was used. This regimen was well tolerated by all patients because frequent orthotic adjustments were made to compensate for growth and to ensure proper fit. In all cases, bracing afforded symptomatic improvement and arrested further skeletal deformity.

Illustrative Case
History

This 13-year-old boy had been diagnosed with Type III OI as an infant, following multiple long bone and rib fractures within his 1st year of life. At age 9, he began to experience holocephalic headaches, hearing loss, gait instability, and a loss of dexterity with fine motor activities, prompting referral to another neurosurgical center. Neurological imaging studies obtained at that time demonstrated basilar invagination, hindbrain herniation, and obstructive hydrocephalus, which was managed with ventriculoperitoneal shunting. One year later, repeat imaging demonstrated further basilar invagination with ventral brainstem compression (Fig. 6 left), which was treated with suboccipital craniectomy, C-1 laminectomy, and duraplasty. No fusion was performed. Following posterior decompression, the patient's symptoms showed transient improvement. However, at the age of 12 years his headaches returned and were accompanied by progressive quadriparesis, dysphagia, and gait ataxia, prompting referral to our institution.

Fig. 6.
Fig. 6.

Sagittal T1-weighted MR images. Left: Severe basilar invagination, ventral brainstem compression, and hindbrain herniation are demonstrated in a 10-year-old boy with OI. Center: Two years later (following suboccipital decompression) further ventral brainstem compression by the invaginated, dysplastic clival—atlantoaxial complex is revealed. Right: Following transoral—transpalatopharyngeal resection of the distal clivus, anterior arch of the atlas, and the odontoid process, the brainstem is decompressed.

Examination

On examination, the patient was found to be extremely short of stature, with height and weight below the fifth percentile for his age. He exhibited the characteristic triangular facies of OI, with frontal bossing and mandibular hypoplasia. Downbeat and rotatory nystagmus, severe conductive hearing loss, diminished gag reflex, and tongue atrophy and fasciculations were evident. Spastic quadriparesis and severe gait ataxia were present as well. Neuroimaging demonstrated severe basilar impression with indentation of the ventral brainstem by the dysplastic clivus—odontoid complex (Fig. 6 center).

Operation

A trial of cervical traction was instituted but did not result in reduction of the deformity. Thus, the patient underwent a transoral—transpalatopharyngeal resection of the distal clivus, anterior arch of the atlas, and odontoid process, followed 1 week later by dorsal occipitocervical stabilization with a titanium loop, braided cables, and autogenous rib graft.

Postoperative Course

The patient's initial postoperative course was unremarkable and repeat imaging obtained prior to discharge demonstrated adequate brainstem decompression (Fig. 6 right). Over the following 6 weeks, the patient's symptoms resolved and he remained asymptomatic for 18 months, at which time the recurrence of mild headaches prompted further radiological investigation. Despite a solid occipitocervical fusion, slight interval progression of basilar impression was noted. External orthotic immobilization with a modified Minerva brace afforded relief of symptoms and arrested further invagination. The patient is now 16 years of age and remains asymptomatic (aside from his fixed hearing deficit) and fully independent in all activities.

Discussion
General Considerations About Basilar Invagination

Basilar invagination is a clinicopathological entity with multiple underlying causes. Regardless of cause, however, the hallmark of this anomaly is occipital bone deformation, a process that involves all three of its anatomical components (basiocciput, exoccipital bone, and supraoccipital bone).40 As a consequence of squamooccipital infolding, the floor of the posterior fossa becomes elevated and the margins of the foramen magnum curve upward.26 The basiocciput is foreshortened and elevated, with the clivus thinned, truncated, and horizontally oriented, creating an obtuse basal and an acute craniocervical angle.15,24,46 Anterolaterally, the petrous portion of the temporal bone is also deformed.26 These changes ultimately permit the clivus-atlas-odontoid complex to assume an abnormally rostral location within the foramen magnum, further restricting the space within the posterior fossa (Fig. 7).

Fig. 7.
Fig. 7.

Drawing (left) depicting the characteristic neural and cranial abnormalities associated with basilar invagination in OI and related osteochondrodysplasias. Note the horizontally oriented clivus, obtuse basal angle, acute craniocervical angle, elevated basiocciput, invaginated clival—atlantoaxial complex, ventrally compressed brainstem, and herniated hindbrain. Sagittal MR image (right) demonstrating many of these same findings in an 11-year-old girl with Hajdu—Cheney syndrome. Note the deformation of the squamooccipital bone, producing the characteristic “tam-o'-shanter” skull configuration.

The rostral extent of invagination dictates attendant neurological manifestations. The brainstem is elevated by and splayed over the ventrally situated clivus-atlas-odontoid complex. In addition to mechanical compression, this creates a fulcrum by which traction is applied to the caudal brainstem and rostral cervical spinal cord, producing prominent bulbar dysfunction and myelopathy. The lower cranial nerves are stretched and distorted as the brainstem is forced upward, yielding characteristic cranial nerve palsies. Cerebellar involvement may be primary, caused by compression from the foramen magnum's infolding posterior and lateral margins, or secondary, as a consequence of hindbrain herniation. Neurological dysfunction may result from several coinciding mechanisms, including direct neural compression, vascular insufficiency (arterial or venous), and/or alterations in cerebrospinal fluid flow dynamics.15,34,37,45

Basilar invagination may be classified as primary (congenital) or secondary (acquired). In its primary form, basilar invagination arises from developmental anomalies of the chondrocranium, notochord, and epichordal elements.26 These congenital anomalies are often associated with other craniovertebral junction abnormalities, including occipitalization of the atlas, Klippel—Feil syndrome, Chiari malformation, and syringohydromyelia.26,46 Secondary basilar invagination (alternatively referred to as basilar impression) arises as a consequence of constitutive skeletal disease. These so-called “bone softening” disorders16,26,30,37 may be congenital, as in OI, spondyloepiphyseal dysplasia, acroosteolysis, Hurler's syndrome, and achondroplasia, or acquired, associated with Paget's disease, osteomalacia, hyperparathyroidism, and renal rickets.1–3,5,6,8,9,11,12,14,15,19,26,28,30–34,39,45,50 In contrast to acquired forms, in which the underlying metabolic and/or biochemical abnormalities may be corrected, congenital basilar impression is characteristically relentless in its progression because of the irreversible nature of the genetically determined errors in bone composition. Thus, any therapeutic intervention must be considered palliative because the fundamental pathology is not addressed.

Classically, the radiological diagnosis of basilar invagination is based on the demonstration of abnormal craniometric relationships on plain radiography or pluridirectional tomography. Many craniometric reference lines have been advocated for this purpose (Table 5). Since the advent of CT and MR imaging, basilar invagination is no longer a diagnosis of inference based on imprecise craniometry; rather, the craniovertebral pathology may be visualized directly, with precise delineation of the nature and extent of neural compression. This, coupled with the capacity to demonstrate associated pathology such as hydrocephalus, syringohydromyelia, and hindbrain herniation, has rendered these imaging modalities indispensable as diagnostic tools in patients with basilar invagination and other craniovertebral junction anomalies. Because CT and MR imaging are complementary techniques, both may be required when assessing complex pathology.

TABLE 5

Selected craniometric lines for diagnosis of BI*

LineProjectionDefinitionNormal FindingsFindings in BI
Wackenheim's (clivus—canal line)latdorsum sellae to tip of clivusentire dens ventral to linedens bisects line
Chamberlain's (palatooccipitallatposterior hard palate to opisthion≤2.5 mm of dens above line (tip oftip of dens >2.5 mm above line
 line) dens usually below line)
McRae's (foramen magnum line)latbasion to opisthionentire dens below line; sagittal canaldens bisects line; neurological
 diameter approximately 35 mm symptoms if sagittal canal
 diameter <19 mm
McGregor's (basal line)latposterior hard palate to lowesttip of dens ≤4.5 mm above linetip of dens >4.5 mm above line
 point of occipital bone (relationship changes w/ flexion-extension)
height index of Klauslatdistance between tip of dens &≥40 mm<30 mm
 tuberculum—cruciate line
Fischgold's digastric (biventerAPconnects the two digastric fossaeentire dens below line; center ofdens bisects line; center of
 line) atlantooccipital joint 10 mm atlantooccipital joint
 below line <10 mm below line
Fischgold's bimastoidAPconnects tips of mastoid processestip of dens 3 mm below—10 mm abovetip of dens >10 mm above line
 line (mean 2 mm above)

AP = anteroposterior; BI = basilar invagination.

Causes of Basilar Invagination in OI and Related Osteochondrodysplasias

The pathogenesis of basilar invagination in OI and the related osteochondrodysplasias remains obscure. Certainly, one may view the bone fragility inherent in these conditions as an inciting, or at least permissive factor. Frank, et al.,11 suggested that the weight of the cranium and its contents exceeds the load-bearing capacity of the “soft” bones at the skull base, deforming them over time. It is probable, as Pozo, et al.,34 postulated, that recurrent microfractures in the region of the foramen magnum underlie the progressive infolding of the posterior skull base. This in turn permits upward translocation of the rostral cervical spine into the posterior fossa. This hypothesis is supported by the frequent intraoperative discovery of thickened, proliferative bone composing the skull base, a finding reminiscent of exuberant fracture callus present at other sites of injury.13,43,44 The high metabolic activity of the reactive bone is confirmed by radioisotope bone scanning, indicating chronic active bone remodeling.20

Given the extent to which the tensile strength and load-bearing properties of bone may be impaired in OI and related osteochondrodysplasias, it is difficult to account for the relative rarity of basilar invagination in patients with these conditions. This phenomenon may be attributed, at least in part, to the genotypic and phenotypic heterogeneity inherent in these disorders.7,13,29,34,43 Osteogenesis imperfecta is notable for its wide clinical and genetic variability, both between and within disease subtypes.13,41–43 More than 20 discrete genetic mutations of type I collagen have been identified in patients with OI; many more have been implicated.7 It is apparent that the type of mutation, its site, and the polypeptide collagen precursor chain involved are all important factors in determining the severity of clinical expression.7 Furthermore, genetic penetrance in these disorders is incomplete and variable; thus, a given genetic defect may confer vastly different phenotypic consequences on two affected individuals.13,43 As such, the spectrum of disease expression is prodigious, ranging from in utero lethality due to total skeletal collapse at one extreme to subclinical manifestation at the other.

Pozo, et al.,34 suggested that patients with OI who develop basilar invagination exhibit only mild forms of the disease (Sillence Type I and IV, or alternatively, OI tarda levis), based on the authors' experience with three cases and a review of seven cases derived from the literature. Subsequently, Harkey, et al.,15 reported basilar impression in two patients with the more severe Type III variant of OI, comprising half of their series. Thus, basilar invagination has been reported in all clinical subtypes of OI except the lethal perinatal (Type II) variant. The present series reflects this distribution, with no predilection for those with milder forms of the disease. Indeed, the majority of our patients manifested the Sillence Type III variant, and most had suffered multiple long bone and/or rib fractures with significant residual skeletal deformity prior to presenting with basilar invagination.

One may question why individuals with Type II OI do not exhibit basilar impression. Certainly, infants born with this subtype have the most severe bone fragility and highest propensity to fracture, because of a profound reduction in type I collagen synthesis (approximately 20% of normal).7 Because of this, however, neonates with this variant rarely survive past infancy; most succumb in the prenatal period.13,32,43 Thus, individuals so afflicted rarely, if ever, attain upright posture. If secondary basilar invagination in OI is caused by repeated microfractures at the skull base, it seems reasonable to assume that these changes could not transpire until the weight of the skull base is loaded on the spine. This does not occur to any great extent until the child stands upright.

It is tempting to apply this line of reasoning to patients with OI Subtypes I, III, and IV, in an effort to explain their variable clinical courses and modes of presentation. In general, we observed that patients who expressed more severe disease (numerous long bone fractures, early and extensive skeletal deformity) tended to develop basilar invagination at a younger age. However, the correlation between overall disease severity and progression of basilar invagination was far from absolute. On rare occasions, a child presented with basilar invagination as the initial manifestation of OI; conversely, a handful of patients with extensive and long-standing pathology of the extraaxial skeleton developed craniovertebral abnormalities as a relatively late complication.

Past and Present Treatment Strategies

Historically, patients with OI, spondyloepiphyseal dysplasia, or Hajdu—Cheney syndrome and basilar invagination have been managed with great trepidation on the part of the physician. Much of this uncertainty may be ascribed to the rarity of these disorders, the infrequency of craniovertebral involvement, and an incomplete understanding of the natural history of such abnormalities if left untreated. Consequently, treatment principles have been derived from anecdotal experience, often with little or no long-term follow-up review. We have synthesized the experience of our predecessors and formulated a comprehensive management strategy that has been applied prospectively for the treatment of secondary basilar invagination in patients with bone-softening syndromes.

Ray37 provided the first account of surgical treatment for basilar invagination in association with OI, using suboccipital and upper cervical decompression without fusion. Subsequent surgical efforts by others used similar techniques and garnered mixed results, ranging from perioperative death to partial functional recovery.9,11,17,18,30,34,38 All too frequently, however, posterior fossa decompression alone provided only transient relief of symptoms followed by inexorable neurological deterioration, occurring within months to years after the initial surgical procedure.15,17,34,38 These experiences serve to emphasize two critical points in the management of basilar invagination caused by bone softening disorders: 1) dorsal decompression alone is inadequate treatment if ventral neural compression is present; and 2) these conditions are characterized by relentless progression, and thus mandate long-term (lifelong) surveillance.

In an effort to improve on the generally disappointing long-term results associated with posterior decompression alone, Harkey, et al.,15 managed four patients with ventral decompression followed by dorsal occipitocervical fusion. Although long-term follow-up data were not available for three of the four cases at the time their report was published, the initial results seemed favorable. Experience with this strategy has been limited, however, and data from other researchers who use such methods have not been forthcoming.

Our treatment algorithm (Fig. 1) reflects an attempt to assimilate the aforementioned concepts with established management principles for craniovertebral junction pathology.26,27,39,46 Hydrocephalus from secondary aqueductal stenosis is a frequent and potentially life-threatening complication in patients with basilar impression and osteochondrodysplasia, and should be treated prior to further intervention. Ventricular shunting will obviate concerns of persistent intracranial hypertension and will occasionally render the patient asymptomatic.

Treatment of the symptomatic patient without hydrocephalus is dictated by the nature and extent of ventral brainstem compression. In nearly all instances, an initial attempt should be made to realign the osseous structures and effect neural decompression by head positioning and cervical traction.26 Traction is applied by means of a halo crown with the head assuming a neutral or slightly extended position; 5 to 7 pounds are applied initially, and the weight is gradually increased until the deformity is reduced or until 12 pounds of traction has proven to be ineffectual over a 5-day period. Cardiorespiratory monitoring is essential during this phase.26 Plain radiographs and MR imaging obtained with the patient in traction are used to determine the adequacy of reduction. Patients in whom ventral neural compression is reducible may be treated with suboccipital craniectomy and upper cervical laminectomy, followed by dorsal occipitocervical stabilization. Particular attention must be given to the posterior decompression even in the absence of tonsillar herniation, because fibrous epidural bands and dural adhesions are often encountered at the posterior cervicomedullary junction.11,26 For stabilization, we favor the use of contoured loop instrumentation to shore up the occiput, because this affords immediate stability to the region and provides load sharing between the implant, bone graft, and native bone structures.15,26,27,35 Devices manufactured of titanium alloy are preferable because they facilitate postoperative imaging.27 As with all fusions, the stability of the construct ultimately relies upon osseous integration; thus the selection, preparation, and application of the bone graft are crucial.27

Ventral brainstem compression not relieved by traction necessitates anterior decompression. This may prove to be technically formidable in operations performed via the standard transoral—transpharyngeal route, because patients with osteochondrodysplasia frequently exhibit micrognathia and restricted oropharyngeal spaces.1,13,20,26,42 If exposure is inadequate, a transpalatal approach may be incorporated; occasionally a LeForte I “drop-down” maxillotomy is required.15,26 These approaches facilitate resection of the anterior arch of the atlas, odontoid process, and distal clivus, thereby relieving brainstem compression directly. Posterior decompression and occipitocervical fusion are mandatory and may be performed immediately following ventral decompression or staged as a separate procedure.

There is controversy concerning treatment of the asymptomatic patient with OI or related osteochondrodysplasia who nonetheless exhibits basilar invagination on imaging studies. Harkey, et al.,15 suggested that prophylactic surgery might be considered for such individuals, because of the potentially devastating consequences of disease progression. Although this is a tenable stance, we have adopted a more conservative approach that incorporates the use of occipitocervicothoracic orthoses in an effort to prevent, or at least retard, further invagination.17 Patients are instructed to wear the custom-modified Minerva jacket at all times except when recumbent, at which times a soft cervical collar may be substituted. This intervention is well tolerated and has prevented progressive deformity in three of four asymptomatic patients so treated in the present series. Close surveillance is mandatory to prevent treatment delays should symptoms occur despite bracing.

Medical and Surgical Outcomes of Intervention

Surgical intervention, regardless of approach, was tolerated quite well in this series, with no deaths or major morbidity incurred. Neural decompression was accomplished in all cases; the fusion rate was 100%. All symptomatic patients improved postoperatively, with 92% achieving good or excellent functional status ratings during their postoperative course (Fig. 8).

Fig. 8.
Fig. 8.

Bar graph depicting functional status ratings for 25 patients with OI or related osteochondrodysplasias and basilar invagination.

Although functional improvement persisted, basilar invagination progressed according to imaging criteria in 80% of cases despite successful fusion. In all patients, the entire fusion mass migrated rostrally as a result of further squamooccipital and petrous bone infolding. Additionally, the posterior fusion mass appeared to act as a fulcrum on which the lever arm of the anterior skull base could turn, thus exacerbating ventral compression. In all cases, Minerva bracing provided ventral cranial base stability, thereby affording symptomatic relief and preventing further skeletal deformity. These findings underscore the progressive nature of the disease process in patients with OI, spondyloepiphyseal dysplasia, and Hajdu—Cheney syndrome. Until the fundamental molecular anomalies underlying these conditions can be addressed, all interventions must be considered palliative, with their primary goal to preserve neurological function for as long as possible.

Conclusions

Basilar invagination secondary to OI and related osteochondrodysplasias presents a formidable challenge to the neurosurgeon because of the progressive and unrelenting nature of these disorders. The following conclusions may be gleaned from the present series: 1) Basilar invagination is an unusual but potentially devastating complication of osteochondrodysplasia. 2) Timely medical and/or surgical intervention leads to a regression of neurological symptoms and retards skeletal deformity. 3) Posterior fossa decompression alone is inadequate treatment for this condition and may hasten progression of ventral brainstem compression. 4) Ventral neural compression should be treated with ventral decompression, followed by dorsal occipitocervical fusion with contoured loop instrumentation to shore up the occiput. 5) Despite solid bone fusion, basilar invagination tends to progress due to further infolding of the occipital and petrous temporal bones around the fusion mass. 6) Prolonged bracing with an appropriate orthotic device (particularly in the period of rapid physical growth during the adolescent years) may halt further invagination and stabilize symptomatic progression.

References

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    Ades LCMorris LLHaan EA: Hydrocephalus in Hajdu-Cheney syndrome. J Med Genet 30:1751993 (Letter)J Med Genet 30:

  • 2.

    Brooks MLGall CWang AMet al: Osteogenesis imperfecta associated with basilar impression and cerebral atrophy: a case report. Comput Med Imag Graph 13:3633671989Comput Med Imag Graph 13:

  • 3.

    Bull JWDNixon WLBPratt RTC: The radiological criteria and familial occurrence of primary basilar impression. Brain 78:2292471955Brain 78:

  • 4.

    Chamberlain WE: Basilar impression (platybasia): bizarre developmental anomaly of occipital bone and upper cervical spine with striking and misleading neurologic manifestations. Yale J Biol Med 11:4874961939Chamberlain WE: Basilar impression (platybasia): bizarre developmental anomaly of occipital bone and upper cervical spine with striking and misleading neurologic manifestations. Yale J Biol Med 11:

  • 5.

    Chandy MJMohammed SH: Osteogenesis imperfecta and basilar impression. Br J Neurosurg 5:2212231991 (Letter)Br J Neurosurg 5:

  • 6.

    Cheney WD: Acro-osteolysis. AJR 94:5956071965Cheney WD: Acro-osteolysis. AJR 94:

  • 7.

    Cole WG: Etiology and pathogenesis of heritable connective tissue diseases. J Pediatr Orthop 13:3924031993Cole WG: Etiology and pathogenesis of heritable connective tissue diseases. J Pediatr Orthop 13:

  • 8.

    Dirheimer YBabin E: Basilar impression and hereditary fragility of the bones. Neuroradiology 3:41431971Neuroradiology 3:

  • 9.

    Fadli ME: Neuropsychiatric complications of osteogenesis imperfecta. “A case with cerebrovascular insufficiency.” J Egypt Med Assoc 51:5285371968Fadli ME: Neuropsychiatric complications of osteogenesis imperfecta. “A case with cerebrovascular insufficiency.” J Egypt Med Assoc 51:

  • 10.

    Fischgold HMetzger J: Etude radio-tomographique de l'impression basilaire. Rev Rheumat 19:2612641952Rev Rheumat 19:

  • 11.

    Frank EBerger TSTew JM Jr: Basilar impression and platybasia in osteogenesis imperfecta tarda. Surg Neurol 17:1161191982Surg Neurol 17:

  • 12.

    Fremion ASGarg BPKalsbeck J: Apnea as the sole manifestation of cord compression in achondroplasia. J Pediatr 104:3984011984J Pediatr 104:

  • 13.

    Gertner JMRoot L: Osteogenesis imperfecta. Orthop Clin North Am 21:1511621990Orthop Clin North Am 21:

  • 14.

    Hajdu NKauntze R: Cranio-skeletal dysplasia. Br J Radiol 21:42481948Br J Radiol 21:

  • 15.

    Harkey HLCrockard HAStevens JMet al: The operative management of basilar impression in osteogenesis imperfecta. Neurosurgery 27:7827861990Neurosurgery 27:

  • 16.

    Hinck VCHopkins CESavara BS: Diagnostic criteria of basilar impression. Radiology 76:5725851961Radiology 76:

  • 17.

    Hunt TEDekaban AS: Modified head-neck support for basilar invagination with brain-stem compression. J Can Med Assoc 126:9479481982J Can Med Assoc 126:

  • 18.

    Hurwitz LJMcSwiney RR: Basilar impression and osteogenesis imperfecta in a family. Brain 83:1381491960Brain 83:

  • 19.

    Kao SCWaziri MHSmith WLet al: MR imaging of the craniovertebral junction, cranium, and brain in children with achondroplasia. AJR 153:5655691989AJR 153:

  • 20.

    Kawamura JMatsubayashi KOgawa M: Hajdu-Cheney syndrome. Report of a non-familial case. Neuroradiology 21:2953011981Neuroradiology 21:

  • 21.

    Klaus E: Röntgendiagnostik der Platybasie und basilären Impression: weitere Erfahrungen mit einer neuen Untersuchsmethode. Fortschr Rontgenstr 86:4604691957Klaus E: Röntgendiagnostik der Platybasie und basilären Impression: weitere Erfahrungen mit einer neuen Untersuchsmethode. Fortschr Rontgenstr 86:

  • 22.

    Kurimoto MOhara STakaku A: Basilar impression in osteogenesis imperfecta tarda. Case report. J Neurosurg 74:1361381991J Neurosurg 74:

  • 23.

    Looser E: Zur Kenntnis der Osteogenesis imperfecta congenita und tarda (sogenannte idiopathische Osteopsathyrosis). Mitteil Grenzgeb Med Chir 15:1612071906Looser E: Zur Kenntnis der Osteogenesis imperfecta congenita und tarda (sogenannte idiopathische Osteopsathyrosis). Mitteil Grenzgeb Med Chir 15:

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    McGregor M: The significance of certain measurements of the skull in the diagnosis of basilar impression. Br J Radiol 21:1711811948McGregor M: The significance of certain measurements of the skull in the diagnosis of basilar impression. Br J Radiol 21:

  • 25.

    McRae DL: Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 40:3353551953McRae DL: Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 40:

  • 26.

    Menezes AH: Congenital and acquired anomalies of the craniovertebral junctionYoumans JRNeurological Surgery: A Comprehensive Reference Guide to the Diagnosis and Management of Neurosurgical Problemsed 4. Philadelphia: WB Saunders199610351089

  • 27.

    Menezes AHRyken TC: Instrumentation of the craniocervical regionBenzel EC (ed): Spinal Instrumentation. Park Ridge, Ill: American Association of Neurological Surgeons19944762Spinal Instrumentation.

  • 28.

    Michie IClark M: Neurological syndromes associated with cervical and craniocervical anomalies. Arch Neurol 18:2412471968Arch Neurol 18:

  • 29.

    Murray LWRimoin DL: Abnormal type II collagen in the spondyloepiphyseal dysplasias. Pathol Immunopathol Res 7:991031988Pathol Immunopathol Res 7:

  • 30.

    O'Connell JEATurner JWA: Basilar impression of the skull. Brain 73:4054261950Brain 73:

  • 31.

    Paradis RWSax DS: Familial basilar impression. Neurology 22:5545601972Neurology 22:

  • 32.

    Pauli RMGilbert EF: Upper cervical cord compression as cause of death in osteogenesis imperfecta type II. J Pediatr 108:5795811986J Pediatr 108:

  • 33.

    Poppel MHJacobson HGDuff BKet al: Basilar impression and platybasia in Paget's disease. Radiology 61:6396441953Radiology 61:

  • 34.

    Pozo JLCrockard HARansford AO: Basilar impression in osteogenesis imperfecta. A report of three cases in one family. J Bone Joint Surg (Br) 66:2332381984J Bone Joint Surg (Br) 66:

  • 35.

    Ransford AOCrockard HAPozo JLet al: Craniocervical instability treated by contoured loop fixation. J Bone Joint Surg (Br) 68:1731771986J Bone Joint Surg (Br) 68:

  • 36.

    Rao SPatel ASchildhauer T: Osteogenesis imperfecta as a differential diagnosis of pathologic burst fractures of the spine. A case report. Clin Orthop Rel Res 289:1131171993Clin Orthop Rel Res 289:

  • 37.

    Ray BS: Platybasia with involvement of the central nervous system. Ann Surg 116:2312501942Ray BS: Platybasia with involvement of the central nervous system. Ann Surg 116:

  • 38.

    Rush PJBerbrayer DReilly BJ: Basilar impression and osteogenesis imperfecta in a three-year-old girl: CT and MRI. Pediatr Radiol 19:1421431989Pediatr Radiol 19:

  • 39.

    Ryken TCMenezes AH: Cervicomedullary compression in achondroplasia. J Neurosurg 81:43481994J Neurosurg 81:

  • 40.

    Schmidt HFischer E: [On partial unilateral synostosis between atlas and axis.] Fortschr Rontgenstr 92:3803841960 (Ger)Fortschr Rontgenstr 92:

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    Sillence D: Osteogenesis imperfecta: an expanding panorama of variants. Clin Orthop Rel Res 159:11251981Sillence D: Osteogenesis imperfecta: an expanding panorama of variants. Clin Orthop Rel Res 159:

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    Sillence DOSenn ADanks DM: Genetic heterogeneity in osteogenesis imperfecta. J Med Genet 16:1011161979J Med Genet 16:

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    Smith R: Osteogenesis imperfecta. Clin Rheum Dis 12:6556891986Smith R: Osteogenesis imperfecta. Clin Rheum Dis 12:

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    Tabor EKCurtin HDHirsch BEet al: Osteogenesis imperfecta tarda: appearance of the temporal bones at CT. Radiology 175:1811831990Radiology 175:

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    Taylor ARChakrovorty BC: Clinical syndromes associated with basilar impression. Arch Neurol 10:4754841964Arch Neurol 10:

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    VanGilder JCMenezes AHDolan KD: The Craniovertebral Junction and its Abnormalities. Mount Kisco, NY: Futura1987The Craniovertebral Junction and its Abnormalities.

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    Wackenheim A: [Radiologic diagnosis of congenital forms, intermittent forms and progressive forms of stenosis of the spinal canal at the level of the atlas.] Acta Radiol Diagn 9:7597681969 (Fr)Acta Radiol Diagn 9:

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    Weil UH: Osteogenesis imperfecta: historical background. Clin Orthop Rel Res 159:6101981Weil UH: Osteogenesis imperfecta: historical background. Clin Orthop Rel Res 159:

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    Williams B: Foramen magnum impaction in a case of acro-osteolysis. Br J Surg 64:70731977Williams B: Foramen magnum impaction in a case of acro-osteolysis. Br J Surg 64:

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    Wycis HT: Basilar impression (platybasia). A case secondary to advanced Paget's disease with severe neurological manifestations. Successful surgical result. J Neurosurg 1:2993051944Wycis HT: Basilar impression (platybasia). A case secondary to advanced Paget's disease with severe neurological manifestations. Successful surgical result. J Neurosurg 1:

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    Ziv IRang MHoffman HJ: Paraplegia in osteogenesis imperfecta. A case report. J Bone Joint Surg (Br) 65:1841851983J Bone Joint Surg (Br) 65:

Article Information

Address reprint requests to: Arnold H. Menezes, M.D., Division of Neurosurgery, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, Iowa 52242.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Chart of algorithm outlining management strategy for patients with basilar invagination and OI or related osteochondrodysplasias.

  • View in gallery

    Lateral (left) and posterior (right) views showing the custom-modified Minerva-type brace, worn by an 11-year-old girl with Hajdu—Cheney syndrome and basilar invagination.

  • View in gallery

    Sagittal T1-weighted MR image demonstrating obstructive hydrocephalus from secondary aqueductal stenosis in a 19-year-old man with OI. Note the horizontally oriented clivus, rostrally displaced pontomedullary junction, and ventral brainstem compression from the invaginated clival-atlantoaxial complex.

  • View in gallery

    Axial CT image obtained in a 13-year-old girl with spondyloepiphyseal dysplasia revealing invagination of the atlas and dens into the posterior fossa, with obstructive hydrocephalus and dilation of the lateral and third ventricles.

  • View in gallery

    Coronal T1-weighted MR image obtained in a 12-year-old boy with Hajdu—Cheney syndrome demonstrating upward translocation of the upper cervical spine into the posterior fossa. Mild hydrocephalus is also evident.

  • View in gallery

    Sagittal T1-weighted MR images. Left: Severe basilar invagination, ventral brainstem compression, and hindbrain herniation are demonstrated in a 10-year-old boy with OI. Center: Two years later (following suboccipital decompression) further ventral brainstem compression by the invaginated, dysplastic clival—atlantoaxial complex is revealed. Right: Following transoral—transpalatopharyngeal resection of the distal clivus, anterior arch of the atlas, and the odontoid process, the brainstem is decompressed.

  • View in gallery

    Drawing (left) depicting the characteristic neural and cranial abnormalities associated with basilar invagination in OI and related osteochondrodysplasias. Note the horizontally oriented clivus, obtuse basal angle, acute craniocervical angle, elevated basiocciput, invaginated clival—atlantoaxial complex, ventrally compressed brainstem, and herniated hindbrain. Sagittal MR image (right) demonstrating many of these same findings in an 11-year-old girl with Hajdu—Cheney syndrome. Note the deformation of the squamooccipital bone, producing the characteristic “tam-o'-shanter” skull configuration.

  • View in gallery

    Bar graph depicting functional status ratings for 25 patients with OI or related osteochondrodysplasias and basilar invagination.

References

1.

Ades LCMorris LLHaan EA: Hydrocephalus in Hajdu-Cheney syndrome. J Med Genet 30:1751993 (Letter)J Med Genet 30:

2.

Brooks MLGall CWang AMet al: Osteogenesis imperfecta associated with basilar impression and cerebral atrophy: a case report. Comput Med Imag Graph 13:3633671989Comput Med Imag Graph 13:

3.

Bull JWDNixon WLBPratt RTC: The radiological criteria and familial occurrence of primary basilar impression. Brain 78:2292471955Brain 78:

4.

Chamberlain WE: Basilar impression (platybasia): bizarre developmental anomaly of occipital bone and upper cervical spine with striking and misleading neurologic manifestations. Yale J Biol Med 11:4874961939Chamberlain WE: Basilar impression (platybasia): bizarre developmental anomaly of occipital bone and upper cervical spine with striking and misleading neurologic manifestations. Yale J Biol Med 11:

5.

Chandy MJMohammed SH: Osteogenesis imperfecta and basilar impression. Br J Neurosurg 5:2212231991 (Letter)Br J Neurosurg 5:

6.

Cheney WD: Acro-osteolysis. AJR 94:5956071965Cheney WD: Acro-osteolysis. AJR 94:

7.

Cole WG: Etiology and pathogenesis of heritable connective tissue diseases. J Pediatr Orthop 13:3924031993Cole WG: Etiology and pathogenesis of heritable connective tissue diseases. J Pediatr Orthop 13:

8.

Dirheimer YBabin E: Basilar impression and hereditary fragility of the bones. Neuroradiology 3:41431971Neuroradiology 3:

9.

Fadli ME: Neuropsychiatric complications of osteogenesis imperfecta. “A case with cerebrovascular insufficiency.” J Egypt Med Assoc 51:5285371968Fadli ME: Neuropsychiatric complications of osteogenesis imperfecta. “A case with cerebrovascular insufficiency.” J Egypt Med Assoc 51:

10.

Fischgold HMetzger J: Etude radio-tomographique de l'impression basilaire. Rev Rheumat 19:2612641952Rev Rheumat 19:

11.

Frank EBerger TSTew JM Jr: Basilar impression and platybasia in osteogenesis imperfecta tarda. Surg Neurol 17:1161191982Surg Neurol 17:

12.

Fremion ASGarg BPKalsbeck J: Apnea as the sole manifestation of cord compression in achondroplasia. J Pediatr 104:3984011984J Pediatr 104:

13.

Gertner JMRoot L: Osteogenesis imperfecta. Orthop Clin North Am 21:1511621990Orthop Clin North Am 21:

14.

Hajdu NKauntze R: Cranio-skeletal dysplasia. Br J Radiol 21:42481948Br J Radiol 21:

15.

Harkey HLCrockard HAStevens JMet al: The operative management of basilar impression in osteogenesis imperfecta. Neurosurgery 27:7827861990Neurosurgery 27:

16.

Hinck VCHopkins CESavara BS: Diagnostic criteria of basilar impression. Radiology 76:5725851961Radiology 76:

17.

Hunt TEDekaban AS: Modified head-neck support for basilar invagination with brain-stem compression. J Can Med Assoc 126:9479481982J Can Med Assoc 126:

18.

Hurwitz LJMcSwiney RR: Basilar impression and osteogenesis imperfecta in a family. Brain 83:1381491960Brain 83:

19.

Kao SCWaziri MHSmith WLet al: MR imaging of the craniovertebral junction, cranium, and brain in children with achondroplasia. AJR 153:5655691989AJR 153:

20.

Kawamura JMatsubayashi KOgawa M: Hajdu-Cheney syndrome. Report of a non-familial case. Neuroradiology 21:2953011981Neuroradiology 21:

21.

Klaus E: Röntgendiagnostik der Platybasie und basilären Impression: weitere Erfahrungen mit einer neuen Untersuchsmethode. Fortschr Rontgenstr 86:4604691957Klaus E: Röntgendiagnostik der Platybasie und basilären Impression: weitere Erfahrungen mit einer neuen Untersuchsmethode. Fortschr Rontgenstr 86:

22.

Kurimoto MOhara STakaku A: Basilar impression in osteogenesis imperfecta tarda. Case report. J Neurosurg 74:1361381991J Neurosurg 74:

23.

Looser E: Zur Kenntnis der Osteogenesis imperfecta congenita und tarda (sogenannte idiopathische Osteopsathyrosis). Mitteil Grenzgeb Med Chir 15:1612071906Looser E: Zur Kenntnis der Osteogenesis imperfecta congenita und tarda (sogenannte idiopathische Osteopsathyrosis). Mitteil Grenzgeb Med Chir 15:

24.

McGregor M: The significance of certain measurements of the skull in the diagnosis of basilar impression. Br J Radiol 21:1711811948McGregor M: The significance of certain measurements of the skull in the diagnosis of basilar impression. Br J Radiol 21:

25.

McRae DL: Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 40:3353551953McRae DL: Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 40:

26.

Menezes AH: Congenital and acquired anomalies of the craniovertebral junctionYoumans JRNeurological Surgery: A Comprehensive Reference Guide to the Diagnosis and Management of Neurosurgical Problemsed 4. Philadelphia: WB Saunders199610351089

27.

Menezes AHRyken TC: Instrumentation of the craniocervical regionBenzel EC (ed): Spinal Instrumentation. Park Ridge, Ill: American Association of Neurological Surgeons19944762Spinal Instrumentation.

28.

Michie IClark M: Neurological syndromes associated with cervical and craniocervical anomalies. Arch Neurol 18:2412471968Arch Neurol 18:

29.

Murray LWRimoin DL: Abnormal type II collagen in the spondyloepiphyseal dysplasias. Pathol Immunopathol Res 7:991031988Pathol Immunopathol Res 7:

30.

O'Connell JEATurner JWA: Basilar impression of the skull. Brain 73:4054261950Brain 73:

31.

Paradis RWSax DS: Familial basilar impression. Neurology 22:5545601972Neurology 22:

32.

Pauli RMGilbert EF: Upper cervical cord compression as cause of death in osteogenesis imperfecta type II. J Pediatr 108:5795811986J Pediatr 108:

33.

Poppel MHJacobson HGDuff BKet al: Basilar impression and platybasia in Paget's disease. Radiology 61:6396441953Radiology 61:

34.

Pozo JLCrockard HARansford AO: Basilar impression in osteogenesis imperfecta. A report of three cases in one family. J Bone Joint Surg (Br) 66:2332381984J Bone Joint Surg (Br) 66:

35.

Ransford AOCrockard HAPozo JLet al: Craniocervical instability treated by contoured loop fixation. J Bone Joint Surg (Br) 68:1731771986J Bone Joint Surg (Br) 68:

36.

Rao SPatel ASchildhauer T: Osteogenesis imperfecta as a differential diagnosis of pathologic burst fractures of the spine. A case report. Clin Orthop Rel Res 289:1131171993Clin Orthop Rel Res 289:

37.

Ray BS: Platybasia with involvement of the central nervous system. Ann Surg 116:2312501942Ray BS: Platybasia with involvement of the central nervous system. Ann Surg 116:

38.

Rush PJBerbrayer DReilly BJ: Basilar impression and osteogenesis imperfecta in a three-year-old girl: CT and MRI. Pediatr Radiol 19:1421431989Pediatr Radiol 19:

39.

Ryken TCMenezes AH: Cervicomedullary compression in achondroplasia. J Neurosurg 81:43481994J Neurosurg 81:

40.

Schmidt HFischer E: [On partial unilateral synostosis between atlas and axis.] Fortschr Rontgenstr 92:3803841960 (Ger)Fortschr Rontgenstr 92:

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