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Source: Wedekind C, et al. Muscle Nerve 2000;23:1868-1871.
Intraoperative electromyographic (EMG) monitoring of facial muscles may be of benefit during surgery in the cerebellopontine angle. Preoperative testing of the facial nerve in these circumstances often reveals various abnormalities of uncertain prognostic value. Are these latter studies necessary?
Prior to the surgical removal of unilateral acoustic neuroma diagnosed by magnetic resonance imaging (MRI), 24 patients, 12 men and 12 women ages 38-68 years, underwent electrodiagnostic studies to determine their value in predicting postoperative facial nerve function. Recording from nasalis, studies included transcranial magnetic stimulation of the contralateral facial motor cortex and ipsilateral cisternal portion of the facial nerve, blink reflex study, facial nerve motor evoked response, and F wave studies. Preoperatively, all patients demonstrated clinically intact facial nerve function and all patients were severely hearing impaired. A retrosigmoid suboccipital approach was used for all and diagnosis was histologically verified. Results were analyzed using Student’s t-test, Spearman rank correlation coefficient, and P values.
Eleven (45.8%) of the operations resulted in severe or total facial palsy. No significant correlation was demonstrated, in either the early or late follow-up period of up to two years, with any of the electrodiagnostic parameters measured. Only tumor diameter correlated with facial nerve function at three months post surgery. Pre-operative electrodiagnostic studies are of no value in predicting facial nerve function following acoustic neuroma surgery.
No comment is made in this paper regarding hearing improvement that may have occurred following surgery. In a Japanese series (Nippon Jibiinkoka Gakkai Kaiho 1995;98:8-15), among 17 acoustic tumors surgically removed 10 (59%) appreciated useful hearing following surgery with 13 showing measurably improved audition. Smaller tumor size, sudden onset of hearing loss, and hearing loss of recent onset were clinical predictors of improved hearing postoperatively. For hearing preservation, tumor size (predictably!) and level of preoperative hearing are the significant predictive criteria (Neurochirurgie 1997;43:8-14). — Michael Rubin