INTRAOPERATIVE MONITORING OF MOTOR CRANIAL NERVES IN SKULL BASE SURGERY

Intraoperative monitoring of cranial nerves is performed to minimize p ostoperative cranial nerve dysfunction. We performed electrophysiologi c monitoring of motor cranial nerves with a NIM 2 unit from Xomed Trea ce and patient multiplexer developed in our clinic. This multiplexer a llows simultaneous monitoring of four cranial nerves and is additional ly equipped with a bipolar stimulation mode. This intraoperative monit oring was used during 102 skull base operations. Of these, 44 operatio ns were acoustic neuroma removals by translabyrinthine approach and 36 by a middle fossa approach. Various operations, including removal of tumors of the jugular foramen and the infratemporal fossa, were perfor med in the remaining 22 patients. The facial nerve, being the most fre quently monitored nerve, was evaluated both preoperatively and intraop eratively. Electrophysiologic data were evaluated with respect to thei r predictive value for postoperative facial nerve function. The relati ve percent decrease in amplitude of the electromyogram after resection compared to that observed before resection seems to be of some predic tive value for the postoperative facial nerve function. A 50 to 60% de crease or more is associated with an increase in the House classificat ion. Intraoperative monitoring is a useful tool in skull base surgery, allowing for safer and faster identification of the motor nerves in p athologic-anatomic conditions. It allows the surgeon a degree of comfo rt by providing immediate information regarding the status of the nerv e. It may also improve postoperative nerve function and shorten operat ing time. Additionally, neuro-monitoring provides some information abo ut expected postoperative facial nerve function.