Feasibility and efficacy of transcranial motor-evoked potential monitoring in neuroendovascular surgery

Abstract

Background and purpose: Neurophysiological monitoring for neuroendovascular procedures typically involves EEG and SSEP monitoring via cutaneous electrodes. MEP monitoring has been used less frequently because, traditionally, this has required subdural electrode placement. With the advent of transcutaneous techniques, MEP monitoring use has increased. However, little has been published regarding the use of this technique in therapeutic neuroendovascular procedures. The purpose of this study was therefore to determine whether TcMEP monitoring is feasible and efficacious in therapeutic neuroendovascular procedures.

Materials and methods: We retrospectively reviewed our data base of therapeutic neuroendovascular procedures performed with the use of TcMEP monitoring. We specifically determined the incidence of TcMEP changes compared with changes in either SSEP or EEG. We then correlated these changes to actual adverse neurologic events.

Results: Although TcMEP monitoring was technically successful in all of the 140 patients in which it was attempted, we observed significant changes in TcMEP signals in only 1 patient. This patient experienced changes involving all 3 monitoring modalities after intraprocedural aneurysm rupture. In contrast, changes in SSEP tracings alone were found in 9 patients. Of these, 2 patients were known to be moribund before their procedures and neither recovered. Among the remaining 7 patients, temporary SSEP changes tended to correlate with temporary neurologic deficits, while permanent changes were associated with permanent or long-lasting deficits.

Conclusions: These results suggest that TcMEP monitoring is feasible in therapeutic neuroendovascular procedures. However, it appears that the addition of TcMEP monitoring provides no added benefit to SSEP and EEG monitoring alone.

Fig 1.

Neurophysiological monitoring tracings from patient 5 after intraoperative rupture (A), showing a decrease in right upper extremity SSEP (left yellow box) and loss of bilateral lower extremity SSEP during aneurysm coiling (center and right yellow boxes). Tracing from a similar time point (B), showing a subtle decrease in amplitude of TcMEP involving the right upper extremity (small left yellow box) and a global loss of EEG (large right yellow box). After EVD insertion (C), recovery of SSEP (yellow boxes) can be seen. Concomitantly, there is a return of the normal TcMEP signal intensity and recovery of EEG (D) (yellow boxes).

Fig 2.

Lateral view of left ICA angiogram (A) from patient 7 shows acute left M1 occlusion (angled arrow) and pericallosal region aneurysm (horizontal arrow). Neurophysiological monitoring tracings (B) show a decrease in right upper extremity SSEP before aneurysm coiling (yellow box). After IV tPA, there is improvement in angiographic opacification of most of the left MCA territory (C), but a posterior frontal M3 branch remains occluded (arrow). In addition, after administration of IV tPA (D), recovery of right upper extremity SSEP is seen (yellow box). After coiling of the aneurysm, thrombus formation was noted at the aneurysm neck (E). This was associated with new monitoring changes (F), specifically a decrease in the left upper extremity SSEP amplitude (left yellow box) and left lower extremity SSEP amplitude (right yellow box). Intra-arterial abciximab (ReoPro) was administered and follow-up angiographic images (G) showed resolution of the thrombus (arrow). Subsequently, SSEP tracings (H) showed minimal recovery of left upper extremity amplitude (left yellow box) and left lower extremity amplitude (right yellow box) by the end of the procedure.