Lessons Learned from Intraoperative Monitoring of Hearing in EMFA Using ECoCh

Abstract

Introduction: Small acoustic neuroma can be removed by EMFA and by retrosigmoid approach. Hearing monitoring during those operations should be a routine procedures. Material and Method: Authors presented their own experience since 2006 and defined changes in intraoperative behavior of surgeon based on monitored hearing during removal of AN by ETLA. Total material of EMFA includes 150 cases. Forty cases were operated with monitoring. Authors analyzed surgical issues causing signs/changes in ECoCh traces and possibly lowering chances for hearing preservation. Results: First signs deteriorating ECoCh traces appeared during localization of landmarks on temporal bone. In this situation, low-speed micromotors with 30,000 rpm. solved problems. Accidentally opening of SSC resulted in lowering of the amplitude in ECoCh. Immediate sealing caused good recovery. More difficult problems encountered during AN resection. When latency elongated of more than 0.10 milliseconds a break in dissection lasting at least 5 minute was recommended. Recurrent latency elongations lowered the chance for hearing preservation. The most vulnerable part of tumor resection was fundus of IAC. Coagulation close to the operating field always influenced on ECoCh morphology. Conclusion: Hearing loss during AN operation can occur in every stage of EMFA. Monitoring of hearing helps in the explanation of dangerous moments of intervention. Most hazardous steps are drilling the roof of IAC, accidentally opening of SSC and dissection close to fundus of internal auditory canal.