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 reliable method for assessing neural degeneration in various conditions affecting the facial nerve. The facial nerve may be subclinically involved by parotid tumors, but estimating such involvement preoperatively may be difficult when facial function is normal. The hypothesis that preoperative ENoG: (1) can detect subclinical facial nerve degeneration as a measure of involvement by parotid tumors and (2) can predict facial nerve function following parotidectomy was prospectively evaluated in the present study.
METHODS: Twenty-two patients undergoing parotidectomy for tumors were tested preoperatively with ENoG, and their facial nerve function was graded pre- and postoperatively (House-Brackmann system). Eight patients had malignant tumors and 14 benign tumors.
RESULTS: In patients with malignant tumors, lower percentage of preoperative ENoG response indicated nerve involvement that was not evident on clinical examination and correlated significantly (p = .035) with postoperative facial nerve dysfunction. Preoperative ENoG reduction of greater than 80% was found in all patients whose facial nerve was infiltrated by tumor. In 14 patients with benign tumors, preoperative ENoG results had no correlation with postoperative facial function.
CONCLUSIONS: In malignant tumors, even when facial function is clinically intact, a low preoperative ENoG response may predict facial nerve involvement 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.