Suprasellar arachnoid cysts: 1. CT recognition.

Suprasellar arachnoid cysts are basal midline masses that represent a rare but surgically remediable cause of hydrocephalus and neurologic deficits. These cysts represent a diagnostic challenge and often go unrecognized for many years. The authors review the computed tomographic (CT) findings in seven patients with documented suprasellar arachnoid cysts and define previously undescribed diagnostic criteria. These cysts usually can be differentiated from cystic midline neoplasms by their CT density, homogeneity, and location as well as by their lack of fat, lack of calcification, and absence of contrast enhancement. Accurate distinction from marked third-ventricular enlargement secondary to obstructive hydrocephalus and from third-ventricular ependymal cysts can be made on the basis of basal cisternal expansion, distinctive mass effect and displacement, the characteristic shape and contour of the apparent "third ventricle," and the appearance of structures at the foramen of Monro. Although metrizamide CT ventriculography and cisternography allow confirmation of the diagnosis and evaluation of cerebrospinal fluid dynamics, these definitive studies will not be obtained unless the cysts are first suspected by their conventional CT appearance.