Suprasellar arachnoid cysts: an extension of the membrane of Liliequist.

A case of suprasellar arachnoid cyst and hydrocephalus diagnosed by computed tomography (CT) and positive-contrast ventriculography is presented. Transfrontal exploration of the 3rd ventricle revealed findings consistent with the cyst being, in fact, a large forward and upward diverticulum of the arachnoidal membrane of Liliequist. The authors suggest that some of the other similarly located arachnoid cysts are extensions of this membrane imperforate by previous infection, hemorrhage, or maldevelopment.