Abstract
Purpose:
Investigation of three strategies of intraoperative monitoring (IM) of auditory function during cerebellopontine angle tumor (CPAT) surgery: transtympanal electrocochleography (TT-ECochG), auditory brainstem responses (ABR), and distortion product otoacoustic emissions (DPOAEs).
Methods and Measures:
Thirty-one patients with CPAT were operated using the middle fossa approach. Auditory function was monitored intraoperatively using TT-ECochG, ABR, and DPOAEs. In all TT-ECochG-monitored patients the following components of compound action potential (CAP) were analyzed: N1-Amplitude, N1-Latency, summation potential (SP). In ABR subjects waves III and V were analyzed. Amplitude and phase of DPOAE were used as the parameters to evaluate the cochlear status intraoperatively.
Results:
In all cases very clear and repeatable CAPs in the TT-ECochG strategy were visualized as a result of 64–128 samples averaged. TT-ECochG morphology including N1-Amplitude, N1-Latency, and SP were displayed and sufficiently analyzed online every 3 to 6 seconds. In a majority of cases ABR measured simultaneously needed 256 or usually more samples in critical moments of tumor removal showing that it is more effective as a supportive than independent strategy of IM of hearing. Also, DPOAE was found to be a very useful tool for IM. DPOAE phase changes were very sensitive for onset of cochlear dysfunction while amplitude was better for evaluation of recovery of cochlear function. A huge inconvenience of the DPOAE application in the operating room is its extreme sensitivity to surrounding noise that in some circumstances excluded DPOAE as a good tool for IM. DPOAE strategy reflecting cochlear activity also needed ABR as a supporting tool for effective intraoperative monitoring of hearing.
Conclusions:
TT-ECochG and DPOAE effectively recorded even very minimal changes in peripheral parts of auditory function in real time but needed to be supported by ABR in these stages of surgery when the more distal part of the cochlear nerve or cochlear nuclei were supposed to be affected. TT-ECochG/ABR or DPOAE/ABR strategy may serve as the most effective tool for intraoperative monitoring of auditory function during CPAT surgery.