Chiari II Malformation

These images demonstrate a small posterior cranial fossa, tectal thickening, towering cerebellum, dysgenesis/marked thinning of the posterior corpus callosum, and inferior cerebellar tonsillar herniation of 10 mm. No flow is appreciated through the cerebral aqueduct on phase contrast imaging. The supratentorial brain demonstrates sequela of prior marked hydrocephalus with suspected rupture of the septum pellucidum, enlarged colpocephalic appearance of the ventricular system and associated pronounced white matter volume loss in the parietal and occipital lobes. The patient has a right parietal ventriculostomy shunt. Findings are characteristic of Chiari II malformation which results from chronic CSF leakage during gestation due to an open neural tube defect (usually myelomeningocele).