[A ruptured aneurysm of the distal posterior inferior cerebellar artery associated with acute subdural hematoma of the posterior fossa: a case report].

We report a case of distal posterior inferior cerebellar artery (PICA) aneurysm associated with acute subdural hematoma (SDH). The patient was a 68-year-old female who was found unconscious at home and transferred to the emergency medical center in a state of deep coma. Her consciousness on admission to the center was 200P (Japan coma scale), E1V1M2 (Glasgow Coma Scale), and the Hunt & Kosnik grade was grade IV. She was in a state of decerebrate condition. Computed tomography (CT) scans revealed diffuse subarachnoid hemorrhage that was located mainly in the posterior fossa, as well as intraventricular hemorrhage in the third and fourth ventricles. It also disclosed an intracerebellar hematoma (ICH) of the vermis and an acute SDH of the left posterior fossa. The first cerebral angiographic examinations on admission demonstrated no aneurysm. However, emergency surgery was performed immediately in order to improve her poor condition. Ventricular drainage and removal of the acute SDH were carried out. Postoperatively, her consciousness improved gradually to 20P. Ventricular peritoneal shunt was performed three weeks later. Her consciousness improved up to 3P and she showed only slight truncal ataxia. She was admitted to our hospital for rehabilitation at two months after the first surgery. Repeated angiography was performed and demonstrated an aneurysm in the telovelotonsillar segment of the left PICA. The aneurysm was successfully clipped via a midline suboccipital approach. Her postoperative course was uneventful, and she continues to undergo rehabilitation. Aneurysms of the posterior fossa associated with acute SDH are extremely rare. Only two cases have been reported for distal PICA aneurysm cases. The CT scans in our patient revealed not only SAH but also SDH in the posterior fossa and ICH in the vermis. Over 100 cases of distal PICA aneurysms have been described in the literature. We analyzed the relationship between the portions with the ruptured aneurysms and CT findings. Aneurysms which were located at the proximal portion of the distal PICA mainly showed SAH and IVH. On the other hand, ICHs of the vermis and cerebellum were characteristic CT findings of ruptured aneurysms which were located more distal to the telovelotonsillar segment, and were evident in 14% of cases of such aneurysms. ICH and SDH were not found in aneurysms which were located in portions more proximal to the telovelotonsillar segment. These characteristic findings were related to the complex anatomical courses of the PICA. The distal portions of the PICA run between the vermis and cerebellar hemisphere, so that if an aneurysm ruptures at these portions, ICHs in the vermis and cerebellum tend to occur. In cases such as ours, because of the characteristic CT findings, effort to detect a distal PICA aneurysm should be made at first surgery, along with ventricular drainage and removal of the SDH. The surgical procedures and outcome of cases with distal PICA aneurysms are also discussed.