[Monitoring of antidromic facial nerve action potentials in cerebello-pontine angle tumor operations].

A method of recording the antidromic facial nerve compound potential (AFNAP) is presented. When the facial nerve is stimulated, a compound action potential is propagated in both directions from the stimulating site. We recorded AFNAP's in 6 cases of cerebello-pontine angle (CP angle) tumors (5 acoustic neuromas and one epidermoid) using a bipolar silver ball-type electrode directly put on the facial nerve in CP angle by stimulation of the peripheral facial nerve at the stylomastoid foramen. It was necessary to use needle electrodes instead of surface ones for stimulation to keep the artefacts from stimulating currents within reasonable bounds. Good contact of the electrode tips with facial nerve was required to get clear action potential. By stimulation with needle electrodes AFNAP's were recorded without averaging and had a good reproducibility. AFNAP's were typical triphasic potentials and the major negative peak latencies were observed from 1.5 to 3.4 msec except one case of recurrent epidermoid whose major negative peak latency was 7.6 msec. It was verified that these potentials were the results of facial activity, because they were recorded exclusively on the facial nerve, they could not be recorded at the proximal end of the sectioned facial nerve, and alterations of latency were observed with changing the position of recording electrode along the facial nerve. A calculated conduction velocity was about 50 m/sec. It was thought that recording AFNAP facilitated the identification of the facial nerve on the surface of the CP angle tumor, because the amplitude of AFNAP decreased immediately when the recording electrodes were off from the facial nerve.(ABSTRACT TRUNCATED AT 250 WORDS)