Diagnosis of ependymal intraventricular cysts of the third ventricle by computed tomography.

The radiological features of seven patients with surgically verified intraventricular ependymal cyst of the third ventricle are presented. In two patients the pre-operative diagnosis was made by ventriculography, in two by ventriculography and computed tomography (CT), and in the last three patients CT alone was sufficient for correct diagnosis: ventriculography was no longer necessary. The third ventricle is indistinguishable from a cyst with an oval or nearly round configuration with a width-to-length ratio varying between 0.53 and 0.91 (mean 0.79). The density of cerebrospinal fluid within the third ventricle/cyst is a little higher than that of the lateral ventricles. A cyst can also be seen within the suprasellar cistern. The septum pellucidum is not widened, and the internal cerebral veins are pushed up between the lateral ventricles. These diagnostic signs show up well in coronal CT sections. The round third ventricle together with the rounded and enlarged frontal horns of the lateral ventricles often give an impression of the head of Mickey Mouse.