The utility of motor evoked potentials (MEPs) for intraoperative neurophysiological monitoring for unclippable complex aneurysms has not been established.
The aim of this study was to evaluate and validate the usefulness of intraoperative MEP monitoring in the treatment of complex aneurysms with and without extracranial-intracranial (EC-IC) bypass.
From among a group of patients who underwent intraoperative MEP monitoring during surgery for aneurysm, between 2007 and 2014, we retrospectively enrolled 17 consecutive patients with complex aneurysms.
Aneurysms were located in the cavernous portion of the internal carotid artery (ICA) in 6, the intracranial portion of the ICA in 6, the anterior cerebral artery in 1, and the vertebral artery in 4 patients. They included 4 large, 7 thrombosed, and 6 dissecting aneurysms. All were treated with parent artery occlusion with or without EC-IC bypass, which included 7 high-flow bypass procedures with radial artery grafting, and 7 low-flow bypass procedures. Of the 17 patients, 6 showed transient or permanent MEP changes. Four of 6 patients showed MEP changes due to temporary occlusion of the recipient artery during bypass construction. However, these changes were reversed by substitution of the recipient artery, intentional hypertension, and shortening of occlusion time. Two patients demonstrated MEP changes when the parent artery was occluded. In one of those two patients, MEP completely disappeared after parent artery trapping, and this remained unchanged until the completion of the surgery without any modification in obliteration of the parent artery. This patient experienced permanent postoperative hemiparesis. The second patient showed significant changes in MEP during temporary ICA occlusion, which however improved after changing the site of occlusion to the common carotid artery (CCA).
In conclusion, intraoperative MEP monitoring has a useful role in the treatment of complex aneurysms—in the selection of the safest and most appropriate recipient artery for EC-IC bypass, and choosing the most appropriate point for occlusion of the parent artery.