When Does Hearing Loss Occur in Vestibular Schwannoma Surgery? Importance of Auditory Brainstem Response Changes in Early Postoperative Phase

Abstract

Some patients suffer postoperative hearing loss even when the intraoperative auditory brainstem response (ABR) is preserved during vestibular schwannomas surgery. This study was conducted to evaluate whether there are dynamic changes of the ABR after surgery. In a prospective study from 2010-2012, 46 patients (24 female and 22 male) with vestibular schwannomas were investigated by intraoperative and postoperative ABR monitoring. Development of ABR quality during and after surgery (Class 1 normal, Class 5 complete loss) was correlated to auditory outcome. At the end of surgery, 17 patients had an ABR Class 1-4 and 29 had Class 5. Four hours after surgery, 9 of 23 (39%) patients showed an ABR quality change, and 24 hours after surgery, 15 of 30 (50%) had undergone ABR quality changes. Four different types of postoperative ABR courses could be distinguished-Course 1: stable with reproducible ABR, Course 2: unstable with reproducible ABR, Course 3: unstable with ABR loss, and Course 4: stable with ABR loss. These courses correlated highly significantly with the intraoperative development (P < 0.001) and with hearing outcome (P= 0.003). The study identifies ongoing changes of ABR quality and hearing function after the end of vestibular schwannoma surgery. Therefore it seems worthwhile to continue ABR monitoring in the postoperative phase in order to identify patients who are at risk of a secondary hearing deterioration and start therapeutic interventions in a timely manner.