INTRAOPERATIVE MONITORING OF MOTOR CRANIA L NERVES IN SKULL BASE SURGERY

Intraoperative monitoring of cranial nerves is performed to minimize p ostoperative cranial nerve dysfunction. We performed electrophysiologi cal monitoring of motor cranial nerves with a NIM 2 unit from Xomed Tr eace and a patient multiplexer developed in our clinic. This multiplex er allows simultaneous monitoring of 4 cranial nerves and is additiona lly equipped with a bipolar stimulation mode. This intraoperative moni toring was employed during 102 skull base operations. Of these 102 ope rations, 44 were acoustic neuroma removals by translabyrinthine approa ch and 36 by a middle fossa approach. Various operations including rem oval of tumours of the jugular foramen and the infratemporal fossa wer e performed in the remaining 22 patients. The facial nerve, being the most frequently monitored nerve, was evaluated both pre- and intraoper atively. Electrophysiologic data were evaluated with respect to their predictive value for postoperative facial nerve function. The relative per cent decrease in amplitude of the EMG after resection compared to that observed before resection seems to be of some predictive value f or postoperative facial nerve function. A 50-60% decrease or more is a ssociated with an increase in the House classification. Intraoperative monitoring is a useful tool in skull base surgery allowing for safer and faster identification of motor nerves in pathologic anatomic condi tions. It allows the surgeon a degree of comfort by providing immediat e information regarding the status of the nerve. It may also improve p ostoperative nerve function and shorten operating time. Additionally n euromonitoring provides some information about expected postoperative facial nerve function.