Pathogenesis of dorsal internal carotid artery wall aneurysms based on histopathologic examination and microscopic configuration

•Blood blister-like aneurysms (BBAs) are an important cause of subarachnoid hemorrhage (SAH).•The specimens of BBAs were obtained intraoperatively from live specimens in two patients.•The pathogenesis of BBAs based on histopathologic examination and microscopic configuration, was suggested. Blood blister-like aneurysms (BBAs) are an important cause of subarachnoid hemorrhage (SAH), but proper treatment is uncertain due to the poor prognosis of these aneurysms. The pathogenesis of BBAs remains unclear and few studies have reported on histological examinations of BBAs because it is difficult to obtain a specimen due to a high risk of intraoperative bleeding. In this report, BBAs were histopathologically examined in two patients who presented with SAH due to rupture of a BBA that was treated with surgical trapping and bypass surgery. BBA specimens including the adjacent internal carotid artery (ICA) walls were obtained intraoperatively. We suggest the pathogenesis of BBAs based on histopathologic examination and microscopic configuration.