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DOI: 10.1055/s-2004-832228
Intraoperative Neuromonitoring of Oculomotoric Function during Supra- and Infratentorial Tumor Resections
For intraoperative monitoring of motor functions of the oculomotor (III), trochlear (IV) and abducens (VI) nerves usually electromyographic potentials of the musculus rectus inferior, rectus lateralis and obliquus superior are registered. This allows one to recognize not stimulated-induced neuronal activity, which can be an indicator of a functional or structural damage to the cranial nerves. Furthermore, selective electrical stimulation allows the identification of individual cranial nerves. Although intraoperative monitoring of electromyographic potentials of ocular muscles can decrease the probability of neuronal damage, it is seldom used because of the potential risk of lesions to the ocular bulbus during placement of the unipolar needles in the muscles. We have investigated alternative conduction forms with the aim to combine a high selectivity of the biosignal for the different nerves with a low risk of needle placement in order to promote this technique for a larger number of intraoperative investigators. In 30 patients undergoing resection of brain tumors located near the course of cranial nerves III, IV and VI we have performed a neuromonitoring of these nerves. Two unipolar needle electrodes for each conduction were placed subdermally under the bulbus in the lower eyelid, lateral of the bulbus and above the bulbus in the upper eyelid. The registration of not induced potentials was possible in all 30 cases. The amplitudes of the potentials allowed in all cases discrimination between the activity of III and VI. In only 22 of 30 cases was a discrimination of activity of IV possible. In the set-up of electrical stimulation to localize them cranial nerves III and VI were identified and discriminated in 28 of 30 cases, nerve IV was identified in 24 of 30 cases. In no case was any pathology as a result of needle placement observed. Intraoperative neuromonitoring of cranial nerves III, IV and VI is feasible by a technique using a conduction mode with near-muscle placement of electrodes. Sensitivity of this method for the identification of cranial nerves III and VI is significantly higher than for cranial nerve IV. The lower success rate for registration of selective activity of vranial nerve IV suggests that this method does not allow us to safely detect functional or structural intraoperative impairment of this nerve. With this limitation the technique presented here still seems to be a safer alternative compared to the traditional mode of intraoperative neuromonitoring of the oculomotor and abducens nerves.