MONITORING OF BRAIN-STEM TRIGEMINAL EVOKED-POTENTIALS - CLINICAL-APPLICATIONS IN POSTERIOR-FOSSA SURGERY

Brain-stem trigeminal evoked potentials (BTEPs) were monitored intraop eratively in 17 patients during posterior fossa surgery. Satisfactory BTEP recording was performed in all patients without technical problem s or interfering with the activity of the operating team. The BTEP was not altered by anesthetic agents or muscle relaxants. Intraoperative monitoring of the BTEP showed wave form alterations or increasing peak latencies in 10 patients. Among these patients, the BTEP demonstrated a dynamic correlation with the surgical process in 8 instances. Two m ajor causative surgical manipulations were identified: cerebellar retr action in 4 cases and tumor dissection from the brain-stem in 6 cases. Withholding the dissection of the tumor, readjusting a cerebellar ret ractor or further modifying the surgical attitude resulted in partial or complete return of the wave form in 7 patients. The BTEP at the end of surgery proved to correlate with the immediate surgical outcome in most instances. We concluded that the intraoperative monitoring of th e BTEP was feasible and suggested, despite the small number of patient s, a potential value in the survey of brain-stem functions during post erior fossa surgery.