Achondroplasia

achondroplasia sagittal T1W

This sagittal T1-weighted MR image demonstrates some of the features found in the skull in achondroplasia. Click on the image for arrows. There is a relatively large cranial vault with small skull base. There is a prominent forehead with depressed nasal bridge (blue arrow). The foramen magnum is narrowed (red arrowheads), and there is a cervicomedullary kink (red line).
Relative elevation of the brainstem gives rise to a large suprasellar cistern (yellow arrow) and a vertically-oriented straight sinus (green arrows).

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.

References:
1. Kao SCS, et al. MR Imaging of the Craniovertebral Junction, Cranium and Brain in Children with Achondroplasia. AJR 153:565-569, 1989.
2. Achondroplasia, eMedicine June 2006

Credit: Dr Laughlin Dawes