Bypass or Not? Adjustment of Surgical Strategies According to Motor Evoked Potential Changes in Large Middle Cerebral Artery Aneurysm Surgery

Abstract

To report the use of neuroelectrophysiologic monitoring to alter the course in aneurysm surgery to minimize postoperative infarction and bypass-related adverse events. Two patients with large middle cerebral artery (MCA) aneurysms were admitted to the authors' hospital. Direct clipping seemed to be difficult, and postoperative paralysis was not rare in the authors' experience owing to prolonged temporal occlusion of the parent artery. Balloon test occlusion (BTO) was positive in one patient, who developed paralysis and aphasia 3 minutes after balloon occlusion of the feeding M1 artery. A bypass procedure seemed to be inevitable in both patients. Motor evoked potentials (MEPs) and sensory evoked potentials (SEPs) were used for monitoring during the operation. For the patient with a positive BTO result, MEP waves did not change until 17 minutes after temporary clip placement. The aneurysm was clipped, and the occlusion time was 24 minutes. MEP waves recovered quickly after reperfusion. In the other patient, there were early changes in MEP waves after temporary clipping. After bypass construction from the temporal artery to the inferior M2 trunk, the time window of safe occlusion was prolonged to 7-8 minutes. Both the aneurysm and the bypassed branch were obliterated, and the clip reconstruction was done to preserve the flow from M1 to the superior M2 trunk. Permanent postoperative disability did not occur in either patient. Intraoperative physiologic monitoring is a complementary method to preoperative BTO to evaluate the window of safe occlusion with high reliability.