Pituitary dysfunction caused by intracranial aneurysms is rare. We report a patient with the unique feature of hyperprolactinemia to a degree previously seen only with prolactinsecreting tumours.

Case report.

A 42-year-old woman had a galactorrhea, left-sided headache, reduced vision in the left eye and a left temporal hemianopsia. Serum prolactin was elevated (365 μg/L). Cranial computed tomography (CT) revealed a suprasellar mass, which carotid angiography showed to be a left internal carotid artery aneurysm. At craniotomy, this aneurysm and a smaller one of the ophthalmic artery were repaired, and the patient's vision returned to normal. The prolactin level fell to normal. Follow-up CT showed no evidence of pituitary adenoma or hypothalamic lesion.

Carotid aneurysm can cause reversible pituitary dysfunction. A prolactin level >300 μg/L is not a reliable cut-off for distinguishing prolactin-secreting adenomas from other causes of elevated prolactin. A co-existing prolactinoma was felt to be ruled out by both a normal CT scan and normal prolactin levels following aneurysm repair. Patients with marked hyperprolactinemia should be considered for angiography or MRI to rule out carotid aneurysm, since the consequences of pituitary exploration in this setting are potentially grave.