Utility of intraoperative monitoring with motor-evoked potential during the surgical enucleation of peripheral nerve schwannoma.

Although it is thought that the surgical enucleation of schwannomas can be easily performed, certain patients present with postoperative neurological symptoms. The present study examined the utility of intraoperative motor-evoked potential (MEP) in predicting neurological deficits following the surgical enucleation of peripheral nerve schwannoma. The current study included 23 patients and MEP was performed using transcranial electrical stimulation. In three cases, the MEP decreased to <50% of the preoperative value; however, in two cases that involved the peroneal nerve and tibial nerve, results appeared to be false positives induced by a tourniquet during surgery. In another case, the MEP was completely lost following enucleation of the tumor from the sciatic nerve, which recovered to 61% of the original MEP within 10 min. This patient presented with common peroneal palsy postoperatively. By contrast, another case involving the lumbar nerve root and in which there was reversible postoperative motor loss, the MEP did not change intraoperatively. Postoperative neurological deficit occurred in 22% of patients in the present study, which is similar to that of previous reports. The present study also demonstrated that even if a nerve is not transected or injured, traction or compression of a peripheral nerve may induce ischemia, which can be monitored using MEP. Although MEP alone was not able to predict postoperative transient sensory or motor deficits, the combination of MEP with other methods of neurological monitoring may improve accuracy and should be investigated in future studies.