Angiographic appearance of a huge retrocerebellar arachnoid cyst in an infant

A detailed analysis of the angiographic findings with a congenital retrocerebellar arachnoid cyst in an infant is reported. The angiographic features are a huge retrocerebellar extra-axial avascular mass compressing and displacing the fourth ventricle anteriorly, dysgenesis of the cerebellum, a tight posterior fossa and transtentorial upward herniation of the monticulus and brainstem.