Abstract
We have been performing experimental and clinical studies on intraoperative monitoring of the cranial nerves. In the present manuscript, methods of intraoperative monitoring of the upper cranial nerves(I〜VI)are reported. Olfactory nerve : Olfactory evoked potentials(OEPs), obtained by electrical stimulation of the olfactory mucosa, were recorded in dogs and humans. In clinical cases, OEPs correlate well with the olfactory function. This method is useful for intraoperative monitoring of olfatory functions. Optic nerve : In dogs, 2 silver ball electrodes were placed on the optic nerve adiacent to the apex of the orbit for electrical stimulation, and another one near the chiasma for recording. Optic nerve evoked potentials(ONEPs)were recorded. Graded transection of the nerves reduced the amplitudes. In clinical cases, ONEPs have good correlation with the optic function. Oculomotor, trochlear and abducens nerves : In dogs, evoked potential elicited by electrical stimulation of the nerves were recorded from surface electrodes around the orbit. Experimental study revealed that most component of the action potentials recorded from surface electrodes originated from EMGs of extraocular muscles. This technique provides noninvasive recording in intraoperative monitoring for ocular motor nerve function. This method is useful to detect the oculomotor, trochlear and adducens nerves. Trigeminal nerves : Motor root of the trigeminal nerve was electrically stimulated and the EMG of the masseter muscle was recorded. This method is useful to distinguish the trigeminal nerve from the facial nerve. At present, these monitoring methods are useful for detecting the nerves and estimating rough functions of the cranial nerves, however, precies correlation of the functions and the findings of intraoperative monitoring should be further studied.
