Electrophysiologic Neuromonitoring Changes during Tumor Surgery in Cerebellopontine Angle

Seo, Dae Won; Park, Kwan; An, Jae Young; Lee, Sang Koo; Chung, Chin Sang; Hong, Seung Bong; Lee, Won Yong; Kim, Byung Joon; Kim, Jong Hyun

Abstract

BACKGROUND: Intraoperative neurophysiologic monitoring(INM) is well known to be useful method to reduce intraoperative complications during tumor surgery in cerebellopontine angle(CPA). We investigated the changes of INM during the surgery. It might be helpful to keep one's eyes on which monitoring modalities are reluctant to change during the operation.
METHODS
We included 49 subjects who had undergone CPA tumor surgery under INM. Their pathology was as follows; vestibular schwannoma in 37, other cranial nerve schwannoma in 3, meningioma in 5 , cyst in 2. The modalities of monitoring were short latency auditory evoked potentials(AEP), somatosensory evoked potentials(SEP) , facial and trigeminal nerve EMG(EMG). Stimulation of SEP was on left or right median, posterior tibial nerves. We studied the frequency of abnormal INM changes and the factors affecting it.
RESULTS
The subjects who had abnormal changes in at least one monitoring modality were 19(38.8.%). AEP changes were in 6.1%, SEP in 12.2% and EMG in 24.5%. The AEP monitoring had no potentials from II through V wave in 28 subjects(57.1%). SEP monitoring had improvement in 2 subjects and aggravation in 6, especially involved in median nerve SEP. Tonic EMG activities were observed in 3 facial muscles of 3 subjects, 2 of 4, 1 of 5. Regarding the pathology of tumor, meningioma had much more changed INM than vestibular schwannoma. The volume of tumor was bigger in abnormal INM group than normal group although it is not statistically significant. Also abnormal SEP and EMG group had bigger mass than normal group.
CONCLUSIONS
INM has frequent electrophysiologic changes during tumor surgery in CPA. Especially EMG can be changed the most frequently. The larger tumor are, the more frequently abnormal changes in INM of CPA tumor surgery are.