Differences and Supplemental use of Transtympanic Electrocochleography and Auditory Brainstem Response Audiometry for Intraoperative Neuromonitoring

Objective: Resection of lesions within the cerebellopontine angle is widely performed using auditory brainstem response audiometry (ABR) for intraoperative neuromonitoring (IOM). Detection of those potentials via transtympanic electrocochleography (ECochG) is also routinely used but particularly for ear and cochlear surgeries. Design: This study therefore evaluates the value of the combined use and differences between both modalities concerning pre- and postoperative hearing impairment by reviewing the recorded intraoperative monitoring data. Materials and Methods: Between 2006 and 2011, we performed 125 consecutive surgeries within the cerebellopontine angle under IOM by ABR and ECochG. The monitoring data were reviewed and related to pre- and postoperative hearing deficit. Results: MEP monitoring was successful in 114 cases (91.2%). Postoperatively, 42.0% of patients showed any degree of new hearing deficit and 3.7% even improved. We recognized a higher variability and oscillation of ECochG potentials. Moreover, amplitudes of ECochG monitoring were significantly higher (0.18 ± 0.04 üV) compared with ABR potentials (0.08 ± 0.006 üV) ( P < 0.05). Additionally, hearing outcome correlated more reliably with the relative perioperative amplitude changes of wave III and V in ECochG (III: P = 0.0008, V: P = 0.0015) than in ABR (III: P = 0.2075, V: P = 0.0398) monitoring. Conclusions: ABR and ECochG monitoring of the hearing system show significant differences. However, for optimal monitoring it seems feasible to combine the more stable ABR with the better detectable and more sensitive ECochG.