NERVUS INTERMEDIUS FUNCTION AFTER VESTIBULAR SCHWANNOMA REMOVAL - CLINICAL-FEATURES AND PATHOPHYSIOLOGICAL MECHANISMS

The results of facial nerve outcome following vestibular schwannoma re moval have generally ignored the sensory component of the nerve. This lack of reporting occurs partly because the distress relating to these functions is less obvious to the surgeon, and partly because the faci al nerve grading systems currently used do not include the functions o f the nervus intermedius. We have estimated the frequency and nature o f abnormalities of nervus intermedius function following vestibular sc hwannoma removal using a retrospective questionnaire. Questionnaires w ere mailed to 257 patients and correctly completed and returned by 224 (87%) of the patients. Prior to surgery 5 (2%) of the patients compla ined of crocodile tears, 9 (4%) noted dryness of the eye, and 15 (6%) complained of an abnormality of taste. Postoperative crocodile tears o ccurred in 98 (44%), an absence or significant reduction in the produc tion of tears was noted in 162 (72%), and a taste abnormality, either a significant reduction or an alteration in character, was noted in 10 7 (48%). The onset of crocodile tears approximated to a bimodal distri bution, and the recovery of nervus intermedius functions was variable. This study has demonstrated that nervus intermedius abnormalities are common following vestibular schwannoma removal. It also documents the ir natural history and discusses the underlying pathophysiological mec hanisms. We suggest that appropriate preoperative counseling be given to all patients undergoing surgery and that the functions of the nervu s intermedius be included in the surgical reporting of facial nerve re sults in cerebellopontine angle surgery.