Isodense colloid cysts of the third ventricle: a diagnostic and therapeutic problem resolved by ventriculoscopy.

Eighteen patients with a colloid cyst of the 3rd ventricle presented to the Frenchay Hospital Neurosurgery Unit. The investigations included computed tomography (CT). Of these patients, 9 had radiographically isodense cysts that caused considerable diagnostic difficulties, being described only as an anterior 3rd ventricular space-occupying lesion and lateral ventricular dilatation in all but 2 cases. The clinical findings are described and the CT appearance is discussed. The new use of ventriculoscopy may resolve the problem rapidly; ventriculoscopy made the diagnosis in 5 cases and confirmed a CT diagnosis in 3 others. (It has also confirmed the diagnosis in 2 cases of hyperdense cysts.) Lately, it has been possible to aspirate the cyst contents endoscopically or, if the colloid is too viscous, to remove it with endoscopic rongeurs. After either of these procedures, the cyst wall can be coagulated with diathermy endoscopically. The method is described, and the advantages over other investigations and treatment are discussed.