Computed tomographic signs of the Chiari II malformation. III: Ventricles and cisterns.

Abstract

In patients with Chiari II malformations, the 4th ventricle is usually not visualized or appears small; the 3rd ventricle is relatively small, typically has a large massa intermedia and only occasionally exhibits parasellar and/or posterior 3rd ventricular diverticula. The lateral ventricles are usually asymmetrically dilated, show medial pointing of the floor of the body near the foramen of Monro, flattening of the superolateral angles and frequent absence of the septum pellucidum. Prior to and after shunting, the interhemispheric fissure may be obliterated or widely open with serrations corresponding to the interdigitated gyri of the cerebral hemispheres. Prominent confluent cisterns at the hind end of the 3rd ventricle in patients with ventricular collapse may represent the CT [computed tomographic] equivalent to the dilated pericallosal, ambient and retropulvinaric cisterns seen in patients with hydrocephalus and poor ventricular filling at pneumography.