The sudden loss of blood supply to the pituitary gland, leading to tissue necrosis and loss of function (PANHYPOPITUITARISM). The most common cause is hemorrhage or infarction of a PITUITARY adenoma. It can also result from acute hemorrhage into sella turcica due to HEAD TRAUMA; intracranial hypertension; or other acute effects of central nervous system hemorrhage. Clinical signs include severe headache; hypotension; bilateral visual disturbances; unconsciousness; and coma.