Differential facial nerve function in tumors of the internal auditory meatus.

Fifty-five consecutive cases of neoplastic involvement of the internal auditory meatus resulting in ipsilateral retrocochlear auditory dysfunction were reviewed. The majority of these tumors (89%) were solitary schwannomas of the eighth nerve. Eleven percent were other tumors. Preoperative facial paralysis was unusual in eighth nerve schwannomas (6.1%) and much more common in other tumors (66.6%). These data tend to suggest that facial paralysis preoperatively increases the probability that the tumor is other than an eighth nerve schwannoma. Furthermore, facial paralysis resulting from an eighth nerve schwannoma indicates a poorer prognosis for ultimate facial nerve function. The small numbers in this series, though far from conclusive, suggest that normally functioning facial nerves may be infiltrated by eighth nerve schwannomas. Failure of eventual recovery of facial nerve function in the postoperative period may suggest tumor infiltration.