Transcranial motor evoked potential monitoring during the surgical clipping of unruptured intracranial aneurysms

Objective: The aim of the present study was to evaluate the usefulness of transcranial motor evoked potential (MEP) monitoring and its impact on morbidity after surgical clipping of unruptured intracranial aneurysms.

Methods: Motor outcomes were compared before and after the application of MEP monitoring for a one year period. A total intravenous anesthesia was induced and maintained with a continuous infusion of vecuronium. Muscle MEPs were elicited by constant voltage stimulation via subdermal needle electrodes placed at C3 and C4 positions. A more than 50% decrement of MEP amplitudes compared with baseline recordings was regarded as a warning sign and promptly indicated to the surgeon.

Results: Before the application of MEP monitoring, a new motor deficit was observed in 3 of 66 patients. However, in 98 patients operated under MEP monitoring, no new motor deficit was found except for one patient who manifested delayed hemiparesis 30 h after the operation owing to a cortical vein injury during craniotomy. MEPs deteriorated in 12 patients which were related to hypotension (n=1), temporary clipping (n=7), and permanent clipping (n=4), and recovered in all after prompt corrective measures. After surgical clipping of unruptured aneurysms, the absence of new motor deficits could be reliably anticipated by recovered MEPs as well as unchanged MEPs.

Conclusions: Transcranial MEP monitoring is a simple, safe, and reliable tool for the prediction of postoperative motor functions. The ischemic complications can be reduced via prompt corrective measures taken on the basis of MEP changes during aneurysm surgery.