Sr. Wolf et al., INTRAOPERATIVE MONITORING OF THE FACIAL-NERVE IN ACOUSTIC NEUROMA SURGERY BY THE ENLARGED MIDDLE CRANIAL FOSSA APPROACH, HNO. Hals-, Nasen-, Ohrenarzte, 41(4), 1993, pp. 179-184
Acoustic neuroma ablation by the enlarged middle cranial fossa approac
h results in a low incidence of postoperative facial nerve dysfunction
. In 25 consecutive patients with tumors in the cerebellopontine angle
with a diameter up to 2.3 cm, intraoperative monitoring of the facial
nerve was evaluated. The facial nerve was monitored electrophysiologi
cally with recordings of the spontaneous EMG and electrically evoked p
otentials (CMAP) from at least three groups of facial muscles. In 4 ca
ses monitoring was helpful for identification and delineation of the f
acial nerve. The mechanically elicited potentials during tumor prepara
tion and CMAP after electrical stimulation close to the brain stem wer
e compared with the postoperative facial nerve function and the time c
ourse of recovery. If the ongoing EMG recordings resulted in potential
s below 0.5 mV and the CMAP at the end of tumor preparation was higher
than 0.5 mV, facial nerve function was normal in 9 of 10 cases on the
first postoperative day. One patient had mild facial palsy. Poor resu
lts could be predicted if numerous discharges with amplitudes higher t
han 0.5 mV and affected CMAP after stimulation near the brain stem wer
e found at the end of surgery. All 3 patients with these findings had
facial paralysis at hospital discharge (an average of 9 days after the
operation). Recovery from the palsies was found to be prolonged. Intr
aoperative monitoring of the facial nerve is now used routinely in sur
gery of the cerebellopontine angle and the internal auditory canal.