[Blood blister-like aneurysm on the posterior wall of the internal carotid artery causing subarachnoid hemorrhage: a case report].

We report a case of blood blister-like aneurysm(BBA)on the posterior wall of the internal carotid artery(ICA)causing subarachnoid hemorrhage(SAH). A 45-year-old man suffering from SAH(WFNS grade 5)was referred to our hospital. 3D-CT angiography showed a BBA on the posterior wall of the ICA. The aneurysm had been enlarged for a few days. Therefore we performed coil embolization. Four weeks after the operation, the aneurysm was found to have regrown. In the second operation the aneurysm was successfully treated by the ICA proximal occlusion with extracranial-intracranial bypass. Postoperative follow-up cerebral angiography detected no aneurysm. To our knowledge, BBA on the posterior wall of the ICA is rare. Radical surgery with bypass should be performed as soon as possible when the BBA is found to regrow. We discuss the clinical characteristics with a review of the literature.