Abstract
Introduction:
Although monitoring facial nerve function intraoperatively has already been effectively developed, such efficacious monitoring of auditory function remains to be established. The aim of this study was to investigate the utility of distortion-product otoacoustic emissions (DPOAEs) for intraoperative monitoring of the cochlear function in humans during removal of cerebellopontine angle tumors (CPATs).
Material and Methods:
Continuous intraoperative monitoring of DPOAEs was performed in 20 of 62 patients undergoing surgical removal of CPATs. All of these 20 patients, who underwent the retrosigmoid approach, had DPOAEs present preoperatively. Depending on the amplitude and frequency band at which DPOAEs were present, monitoring was carried out at 2.0 to 6.0 kHz with primary stimulus tone amplitudes of 60 to 70 dB SPL.
Results:
In patients operated for CPATs, various patterns of DPOAE amplitude reductions and recoveries were observed. DPOAEs recorded from the basal part of the cochlea (i.e., high frequencies) changed earlier and more profoundly than those from the middle and apical sections (i.e., lower frequencies). In some cases cochlear function was affected irreversibly as reflected by loss of DPOAEs. Microcoagulation of small vessels, tumor debulking, and compression or stretch of the internal auditory canal contents were found to be procedures affecting DPOAEs. The status of DPOAEs at the conclusion of tumor dissection correlated with postoperative hearing levels.
Conclusions:
DPOAEs were used to monitor in the real-time domain auditory function during CPAT removal surgeries. The status of DPOAEs at the conclusion of the operations was related to the postoperative hearing.