Some new angiographic observations in patients with Chiari type I and II malformations.

Angiographic abnormalities of the lower hindbrain seen in 13 cases of Chiari Type I and Type II malformations are described. Previously reported findings are assessed, particularly deformities of the posterior inferior cerebellar artery (PICA). Caudal displacement of the cerebellar tonsils without other angiographic localizing signs of an expanding intracranial mass suggest a Chiari malformation. In such cases it is helpful to demonstrate a low cephalic loop of the PICA, reflecting caudal displacement of the fourth ventricle. Associated angiographic demonstration of significant intraspinal localization of the brainstem is pathognomonic of Chiari malformation.