[The significance of the cerebellar tonsillar herniation on the cause of sudden death of ruptured cerebral aneurysm].

We experienced a case with sudden unexpected death caused by rupture of an intracranial aneurysm, which was confirmed by autopsy. Depending on this case, we reported the significance of the cerebellar tonsillar herniation on the cause of sudden death of ruptured cerebral aneurysm. A 58-year-old man was admitted to us for treatment of subarachnoid hemorrhage (SAH). The CT scanning showed diffuse SAH in the whole cistern. Cerebral angiography on admission revealed an aneurysm at the bifurcation of the left middle cerebral artery in association with bleb like configuration. The aneurysmal neck was clipped on the day of admission. The postoperative course was uneventful. In the early morning of postoperative 23rd day, he was found being expired. To clarify the cause of death, an autopsy was done, disclosing diffuse SAH in association with tonsillar herniation more marked on the left. Thus, the distortion of the spinomedullary junction due to asymmetrical herniation was considered to be responsible for unexpected sudden death in this case. Examination of the major cerebral artery disclosed a ruptured anterior communicating artery aneurysm.