[MEP showed peculiar changes after temporal ICA occlusion in aneurysm surgery, in spite of cerebral tolerance to preoperative test occlusion. A case report].

Preoperative balloon test occlusion (BTO) has generally been used to predict intraoperative tolerance for temporary vascular occlusion to prevent a premature rupture during aneurysm surgery or to perform complete treatment for large aneurysms. We encountered a case in which intraoperative motor evoked potential (MEP) revealed peculiar changes after temporal occlusion of the internal carotid artery during aneurysm surgery, in spite of showing sufficient tolerance to preoperative BTO. We emphasize the importance of intraoperative MEP monitoring, even if patients have shown tolerance in preoperative BTO.