[Dissecting aneurysm of the posterior inferior cerebellar artery; a case report].

A case of a dissecting aneurysm of the left posterior inferior cerebellar artery caused by giant cell angiitis is presented. A 22-year-old woman was admitted on August 30, 1990, with sudden onset of severe occipital headache and vomiting. Neurological examination on admission only showed severe meningismus. CT scan demonstrated subarachnoid hemorrhage and a small hematoma in the 4th ventricle. A left vertebral angiogram demonstrated that the left posterior inferior cerebellar artery was occluded at the lateral medullary segment. We diagnosed subarachnoid hemorrhage from a dissecting aneurysm. On the day following admission, the patient underwent a left suboccipital craniectomy. The posterior inferior cerebellar artery was enlarged for a distance of about 8 mm and there was typical purplish-red appearance in the dissecting aneurysm. This aneurysm was excised after trapping. The histological diagnosis was primary localized giant cell angiitis without systemic involvement. The etiology of the intracranial dissecting aneurysm is obscure, but this report suggests that cerebral angiitis can be considered as an important factor.