Systematic facial nerve monitoring in middle ear and mastoid surgeries: “Surgical dehiscence” and “electrical dehiscence”

ObjectivesTo evaluate and systemize intraoperative facial nerve monitoring (IOFNM) in middle ear and mastoid surgeries.Study design and settingA prospective study.MethodsIOFNM was performed in 100 patients undergoing middle ear and mastoid surgeries. We checked “surgical dehiscence” under microscopes, and also estimated the minimal threshold of electric current needed to change the electromyography of facial muscles using Nerve Integrity Monitor (NIM)-2 (Xomed, Minneapolis, MN, USA).ResultsForty-three percent of cases showed “surgical dehiscence” and responded to electric stimulation of 0.7 mA or less. “Electrical dehiscence” (≤ 0.7 mA) was presented in 73 (73.0%) cases, and 82.2% of these cases responded to 0.4 mA or less. The mean threshold of minimal electrical stimulation was 0.29 mA for tympanic segments and 0.41 mA for mastoid segments.ConclusionsWe recommend an electrical stimulation of 0.7 mA for the first screening and 0.4 mA for the second exploration in order to define the facial nerve using intraoperative NIM-2 monitoring in middle ear and mastoid surgeries.