Progressive coma after the transsphenoidal decompression of a pituitary adenoma with marked suprasellar extension: report of two cases. Two cases of neurological deterioration and coma after the transsphenoidal decompression of a pituitary adenoma with marked suprasellar extension and invasion of the 3rd ventricle are presented. Emergency ventricular shunting led to prompt neurological improvement, which, supplemented by radiation therapy, allowed long-term amelioration of symptoms. Three possible explanations for this complication are offered: 1) traction of the attached 3rd ventricle into the decompression site, causing increased obstructive hydrocephalus, 2) vasopressin release by surgical manipulation of the pituitary stalk and circumventricular organs causing cerebral edema, and 3) edema in the residual tumor secondary to surgical manipulation causing further hydrocephalus. Subsequent patients with similar clinical and imaging criteria will have a planned perioperative ventricular shunting procedure performed. 