[Ruptured fusiform aneurysm of the basilar artery with minimal atherosclerosis--report of a case].

We reported a case of ruptured fusiform aneurysm of the basilar artery with minimal atherosclerosis. A 51-year-old man was admitted because of subarachnoid hemorrhage (SAH). He had no previous illness and family history. Computed tomographic scan revealed subarachnoid hemorrhage and a fusiform aneurysm in the basilar artery. Cerebral angiography confirmed the presence of the basilar fusiform aneurysm. After four days, the consciousness level worsened and a respiratory support was initiated. The patient died on the fifth hospital day. Autopsy was permitted only to the brain. The brain weighed 1,700 g. Massive subarachnoid hemorrhage was noted at the base of the brain and in the sylvian fissures. A large fusiform aneurysm (30 x 20 x 17 mm) was located in the proximal portion of the basilar artery. Atherosclerotic changes were minimal in the aneurysmal wall and the major extracerebral arteries. SAH was most severe around the aneurysm. The pons showed focal necrosis due to compression by the aneurysm. Microscopically, the aneurysmal wall revealed diffuse attenuation of the muscularis. The elastica also showed a focal defect. We suggest that in the present case of fusiform aneurysm, the pathogenesis is not atherosclerosis but a congenital defect of the muscularis and elastic lamina.