PREOPERATIVE ELECTRONEUROGRAPHY (ENOG) IN PAROTID SURGERY - ASSESSMENT OF FACIAL-NERVE OUTCOME AND INVOLVEMENT BY TUMOR - A PRELIMINARY-STUDY

Background. Facial electroneurography (ENoG) is an established and rel iable method for assessing neural degeneration in various conditions a ffecting the facial nerve. The facial nerve may be subclinically invol ved by parotid tumors, but estimating such involvement preoperatively may be difficult when facial function is normal. The hypothesis that p reoperative ENoG: (1) can detect subclinical facial nerve degeneration as a measure of involvement by parotid tumors and (2) can predict fac ial nerve function following parotidectomy was prospectively evaluated in the present study. Methods. Twenty-two patients undergoing parotid ectomy for tumors were tested preoperatively with ENoG, and their faci al nerve function was graded pre-and postoperatively (House-Brackmann system). Eight patients had malignant tumors and 14 benign tumors, Res ults. In patients with malignant tumors, lower percentage of preoperat ive ENoG response indicated nerve involvement that was not evident on clinical examination and correlated significantly (p = .035) with post operative Facial nerve dysfunction. Preoperative ENoG reduction of gre ater than 80% was found in all patients whose facial nerve was infiltr ated by tumor. In 14 patients with benign tumors, preoperative ENoG re sults had no correlation with postoperative facial function. Conclusio ns. in malignant tumors, even when facial function is clinically intac t, a low preoperative ENoG response may predict Facial nerve involveme nt by the tumor. The lower the preoperative ENoG response, the poorer is the expected postoperative facial nerve function. There was no such correlation in benign parotid tumors. (C) 1998 John Wiley & Sons, Inc .