The significance of intraoperative monitoring of muscle motor evoked potentials during unruptured large and giant cerebral aneurysm surgery

Abstract

The goal of this study was to characterize the utility of muscle motor evoked potentials (MMEPs) elicited by direct cortical stimulation as a means of monitoring during unruptured large and giant cerebral aneurysm surgery. This analysis focused on intraoperative changes in MMEPs and their relationship to postoperative motor function. The study population consisted of 50 patients who underwent surgery for large (n = 31) or giant (n = 19) cerebral aneurysms. Intraoperative MMEPs were continuously and successfully obtained in muscles belonging to the vascular territory of interest. There was no postoperative motor paresis in 31 (62%) patients in whom intraoperative MMEPs remained unchanged. Transient MMEP change occurred in 15 (30%) of the 50 patients, but 9 of those patients had no postoperative motor deficits, 5 had transient motor deficits, and 1 suffered permanent motor deficits resulting from postoperative delayed blood flow insufficiency due to arteriosclerosis of the parent artery. Permanent MMEP loss occurred in 4 (8%) of 50 patients, all of whom developed severe and permanent postoperative motor deficits. MMEP is a useful monitoring modality in patients undergoing surgery for large or giant cerebral aneurysms. This strategy can help predict functional prognosis or guide the neurosurgeon intraoperatively in an effort to promote better outcomes.

Fig. 1

A: Three dimensional-computerized tomography angiography demonstrated a giant aneurysm (25 mm) at the C1 portion of the left internal carotid artery. B: Although MMEP loss occurred in response to prolonged vessel occlusion, the amplitude of MMEPs recovered to control levels several minutes after termination of vessel occlusion. C: The aneurysm was occluded using six fenestrated clips, not involving any branches or perforating vessels. D: Postoperative magnetic resonance imaging showed a fresh infarction in the anterior choroidal artery territory. MMEP: muscle motor evoked potential.

Fig. 2

A: 3D-CTA demonstrated a thrombosed giant aneurysm (40 mm) at the M1 portion of the right MCA. B: A thrombosed giant aneurysm (40 mm) at the M1 portion of the right MCA after STA-M2 double anastomosis was shown schematically. C: A vasorecontructive M1 with part of the incised aneurysmal wall using 6-0 Proline was illustrated. D: After trapping and reopening of the M1 segment, thrombus formation within the vessel was verified (intraoperative photograph). E: After trapping and removal of the M1 segment, recirculation of blood flow in the perforating artery at the distal portion of the M1 was shown schematically. F, G: Postoperative magnetic resonance imaging revealed a fresh infarction in the right lenticulostriate artery territory and 3D-CTA showed removal of the giant aneurysm and bypass patency. IC: internal carotid, LSA: lenticulostriate artery, MCA: middle cerebral artery, PcomA: posterior communicating artery, STA: superficial temporal artery, 3D-CTA: three dimensional-computerized tomography angiography.