Visual hallucinations associated with pituitary adenoma.

Visual hallucinations were the presenting symptom in three patients with pituitary adenoma. One patient reported only simple unformed hallucinations, which are a well-documented phenomenon occurring in lesions compressing the optic nerves and chiasm. The other two patients, however, experienced complex formed visual hallucinations believed to be of the release type. No evidence of seizure activity responsible for the hallucinations was found; the mechanism producing them is discussed with correlation to operative findings and electrophysiological studies.