Intraoperative Neurophysiological Monitoring during Brainstem Surgery

Background: Removal of brainstem lesions if one of the most difficult procedures in neurosurgery. Intraoperative monitoring is used to avoid impending damage to these highly eloquent structures. However, data of neurophysiological monitoring during brainstem surgery is lacking. Methods: Consecutive patients with brainstem lesions who underwent surgical removal from June 2007 to December 2012 were retrospectively analyzed. Transcranial motor evoked potential (MEP) and somatosensory evoked potential (SSEP) were performed in all cases. The monitoring data were reviewed and related to new postoperative motor deficit and postoperative imaging. Clinical outcomes were assessed during follow-up. Results: Total 19 consecutive cases of brainstem cavernomas were identified. MEP and SSEP monitoring was successful in 18 cases (94%). In 13 (73%) of all cases, MEP and SSEP were stable throughout the operation, but 5 patients (28%) developed a new neurological deficit. In four cases (22%) MEP and SSEP were permanently lost, but only one patient had a permanent new neurological deficit. In one case MEP and SSEP were temporarily lost and the patients did not develop any new neurological deficits. Conclusion: Continuous MEP and SSEP monitoring do not provide sufficient monitoring during brainstem surgery as high rates of false positive and false negative results are encountered. Further development in this area is still needed.