Electroneurography: preoperative facial nerve assessment for tumors of the temporal bone

Tumors of the temporal bone and cerebellopontine angle may be associated with subclinical facial nerve degeneration, despite clinically normal facial function. To determine if preoperative neurophysiologic testing might predict postoperative facial function after tumor surgery, preoperative facial electroneurography (ENoG) was performed in 82 patients with confirmed tumors of the temporal bone and cerebellopontine angle. In patients with acoustic neuroma, preoperative ENoG amplitude reduction varied directly with tumor size. In addition, a statistically significant association between impaired postoperative facial function and acoustic neuroma size greater than 2.5 cm was found. However, preoperative ENoG amplitude reduction did not accurately predict postoperative facial function. These findings suggest that factors, such as the type and size of tumor, the microanatomic relationship between the facial nerve and the neoplasm, and/or desynchronization of the evoked motor-unit volley, may effect results obtained with ENoG in this setting.