Platybasia and basilar invagination

Case contributed by Hidayatullah Hamidi
Diagnosis certain


Progressive right side gait ataxia and diplegia

Patient Data

Age: 25 years
Gender: Male

Acute cervicomedullary angle and ventrally compressed brainstem. Herniated of hindbrain, and invaginated clival-atlantoaxial complex

The clivus has a completely horizontal orientation (platybasia). There is mass effect over the brain stem and mild dilation of the lateral and third ventricles is noted. There is arrested cerebellar tonsils posterior to the body of C2 and the opisthion.

Additionally there is partial fusion of C5 and C6 vertebral body.

No evidence of siryngomyelia in the imaged cord.


A. Clivoaxial angle = 83 degree (cut-off value: 138.5 degree)

B. Clivodens angle= 69.8 degree( cut-off value: 123.5 degree)

C. Clivopalate angle= 6.6 degree (cut-off value: 53.5 degree)

D. Odontoid pig above Chamberlain’s line: 20 mm (cut-off value: 3 mm)

E. Skull base angle: 172 degree (cut-off value: 143 degree)

Case Discussion

A severe case of platybasia and basilar invagination.

Platybasia can be caused by a wide variety of congenital and acquired diseases, however no further clinical and radiographic data of the patients was available.

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