Image-guided placement of eye muscle electrodes for intraoperative cranialnerve monitoring

OBJECTIVE: Monitoring of the oculomotor system during cranial base or brain stem surgery requires extraocular intraorbital insertion of electromyograph y electrodes. We investigated the use of image-guidance technology for anat omically correct intraorbital electrode placement. METHODS: For neuronavigation, an optical tracking system was used in a stan dard fashion. Needle electrodes were inserted percutaneously into the later al rectus, inferior rectus, and superior oblique muscle along the axis of a hand-held pointer or by means of an electrode applicator to allow direct t racking with the navigation system. Electromyographic monitoring was perfor med by multichannel recordings of free running or evoked activity from the selected muscles. RESULTS: We have used this method in 10 patients; 5 had cranial base tumors and 5 underwent operations for brainstem lesions. No additional instrument s or resources were required compared with the routine setup, and no intrao rbital structures were injured. Successful monitoring of oculomotor, trochl ear, or abducent nerve function was possible in each case. CONCLUSION: This method may have the potential to increase the safety and s uccess rate of intraoperative electro-ophthalmography during microsurgery f ocused on preservation of neurological function.