Foramen magnum Stenose bei Achondroplasie

Achondroplasia is the most common cause of short-limb dwarfism. (For a general discussion, see the generic article on achondroplasia.)

As the skull base forms by endochondral ossification whereas the skull vault by membranous ossification, there is a marked discrepancy in relative size as the skull vault, brain and cord grow normally whereas the skull base remains small.

As a result of this size discrepancy, there is stenosis of the foramen magnum, often with basilar invagination. Compression of the medulla may result in quadriparesis, sleep apnea, and even sudden death. Interruption to normal cerebrospinal fluid (CSF) flow can lead to hydrocephalus.

Radiographic features

Cranial content
Cervico-medullary junction
  • foramen magnum narrowed
  • obliteration of the CSF space around the cervicomedullary junction
  • increased intramedullary T2 signal sometimes seen, representing myelomalacia and gliosis 

Treatment and prognosis

Surgical decompression may be required, with resection of the posterior aspect of the foramen magnum, the posterior arch of C1 and duroplasty.

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