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There is a relatively large cranial vault with small skull base. There is a prominent forehead with depressed nasal bridge. The foramen magnum is narrowed, and there is a cervicomedullary kink. Relative elevation of the brainstem gives rise to a large suprasellar cistern and a vertically-oriented straight sinus.
This sagittal T1-weighted MR image demonstrates some of the features found in the skull in achondroplasia.
There was moderate enlargement of ventricles and surface CSF spaces consistent with communicating hydrocephalus. CSF flow studies demonstrated flow around the craniocervical junction. MR venography demonstrated restricted flow in the sigmoid sinuses and jugular bulbs, which probably contributed to the hydrocephalus.
Craniocervical junction constriction can give rise to problems in achondroplasia including sleep apneoa, sudden apneoas, sudden death, and myelomalacia. Surgical decompression may be helpful in selected cases.
Image contributed by: Dr Laughlin Dawes