Chiari III malformation - repaired
Surgery at birth. Now progressive ataxia.
MRI brain and upper cervical spine
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The posterior fossa is markedly hypoplastic with focal defect in the midline occipital bone associated with distortion of the left occipital lobe and posterior fossa structures toward the defect, consistent with site of initial meningo +/- encephalocoele.
Hypoplastic left cerebellar hemisphere present with almost complete aplasia of the right hemisphere and vermis. The mid brain is elongated in the anteroposterior plane with deepening of the interpeduncular cistern and dorsal opening of the tectal plate and fourth ventricle posteriorly. The upper portion of the cervical cord is also open, continuous with the central canal of the cord to the C2 level. The ventricular system is dilated but without definite features of aqueduct stenosis. No transependymal edema. Distortion of the left occipital horn with loss of overlying parenchyma medially, likely related to dysplasia +/- post surgical change. The corpus callosum is dysplastic, the posterior half of the body and the splenium being relatively small but still present.
The pons is atrophic. No enlargement of the massa media and the colliculi are hypoplastic rather than prominent. The superior cerebellar peduncles are mildly thickened.
This case highlights the difficulty in assessing congential malformations which have had neonatal surgery. Overall the features most likely represent a repaired chiari III malformation.