Third nerve palsy: the presenting sign of a pituitary adenoma in five patients and the only neurological sign in four patients.

Five male patients sought medical attention for diplopia and were found to have third nerve palsies secondary to pituitary adenomas. In four cases this was the only neurologic abnormality. In the fifth there was an additional, asymptomatic, temporal visual field defect in one eye. Partial third nerve involvement was seen in all but one patient. Four patients underwent successful surgery and were found to have chromophobe adenomas. One patient had clinical and laboratory evidence of Cushing's syndrome. An initial diagnosis of cerebral aneurysm was made in three cases when the third nerve palsy followed a severe, acute headache. Later it became evident that pituitary apoplexy was the correct diagnosis. The mechanisms by which a pituitary adenoma causes a third nerve palsy are discussed. The importance of recognizing a pituitary tumor as the etiology of an isolated third nerve palsy is emphasized.