Intraoperative motor-evoked potential monitoring during coil embolization of internal carotid–anterior choroidal artery aneurysms: A comparative case series and lessons on monitoring pitfalls

Background: Ischemic injury to the anterior choroidal artery (AChA) territory during coil embolization of internal carotid artery–AChA (ICA–AChA) aneurysms can be functionally devastating and is not always detected by angiography. We examined the utility and the interpretive pitfalls of intraoperative motor-evoked potential (MEP) monitoring in this specific aneurysm subgroup. Methods: We retrospectively reviewed 16 consecutive patients who underwent coil embolization for ICA–AChA aneurysms at a single institution. Seven patients (2013–2025) were monitored with intraoperative MEP (MEP group); 9 patients (2005–2015) treated before monitoring was introduced served as a historical comparison group (non-MEP group). Angiographic AChA changes, MEP waveform changes, intraoperative interventions, and postoperative diffusion-weighted magnetic resonance imaging were analyzed. Results: Significant MEP amplitude reduction (≥50%) occurred in two monitored patients, prompting coil retrieval, microcatheter repositioning, or a procedural pause; amplitudes recovered in all. One patient showed transient MEP reduction without angiographic change (possible false-positive). No patient in the MEP group developed postoperative infarction (0%), whereas two of nine non-MEP patients did (22%). Conclusion: In this small comparative series, MEP monitoring provided functional information complementary to angiography, with no infarctions in the monitored group. MEP changes must be interpreted alongside angiographic and clinical findings, as both false-positive and false-negative results occur. These hypothesis-generating findings warrant prospective validation.