Electoroneuronography (ENoG); Preoperative Facial Nerve Assessment for Parotid Gland Tumors.

Parotid gland tumor are often associated with carcinomatous infiltration into facial nerves without overt manifestations of facial nerve palsy, which makes preoperative predictions of carcinomatous infiltration difficult. ENoG has been shown to be a useful approach to evaluate facial nerve degeneration. Here, we measured facial nerve function by performing ENoG preoperatively on patients with parotid gland tumors prior to investigate the usefulness of ENoG in preoperative examination of these tumors.Subjects: Twenty healthy individuals without any history of facial nerve palsy and 18 patients with parotid gland tumors (13 with benign tumors and 5 with malignant tumors) but no overt facial nerve palsy.Results: Mean ENoG values obtained for each groups were 103.5% (control), 82.2% (benign) and 48.1% (malignant). The mean ENoG values for the malignant group was significantly different compared to the other two groups (p<0.05). Differences in sizes or regions of tumors did not affect ENoG values significantly.Conclusion: ENoG was useful for the preoperative evaluation of facial nerve function. We suggest that a 50% reduction or more in ENoG values may predict the malignancy of tumor and a high risk for carcinomatous infiltration into facial nerves without any manifestations of facial nerve palsy.