A ruptured distal posterior inferior cerebellar aneurysm. Our case and review of the literature.

We present a case of ruptured distal posterior inferior cerebellar artery (PICA) aneurysm, and review the literature and discuss the treatment strategy. A 77-year-old woman presented with the sudden onset of severe headache, nausea and vomiting. Computed tomography revealed an intraventricular hemorrhage, predominantly in the fourth ventricle and hydrocephalus with a thin subarachinoid hemorrhage (SAH). Angiography revealed an aneurysm arising at the turning point of the vessel, from the telovelotonsillar segment of the right PICA. On the 17th day after the onset, repeated angiography revealed a smaller aneurysm than the one detected on the first day at the same place and with no spasm. On the 22nd day, the aneurysm was proved to be partially thrombosed and was safely clipped via a right lateral suboccipital approach. SAH with a fourth ventricular hemorrhage or an isolated fourth ventricle hemorrhage should raise the suspicion of a distal PICA aneurysm. Aneurysms of the distal PICA have often been reported to arise at a turning point of the artery rather than at a junction of the vessel. It is suggested that the pathogenesis could be hemodynamic stress that has developed due to embryological factors. Distal PICA aneurysms have often gone detected in many previous cases because of thrombosis inside the aneurysms. Thus, particularly in the case of intentionally delayed surgery, we recommend repeated angiography under various conditions to identify how the aneurysm develops just before surgery.