Electrocochleographic evaluation of hearing loss in acoustic neuromas

Objective: This study aimed to clarify the pathophysiology involved in the cause of hearing impairment due to acoustic neuromas (AN) with electrocochl eograph (ECoG). Study Design: The study design was a retrospective case study. Setting: This study was conducted in a tertiary referral center. Patient: Thirty-four patients diagnosed as having AN by magnetic resonance imaging between 1988 and 1995. Intervention: Diagnostic. Main Outcome Measures: The authors made a comparison between the patients' ECoG findings and the size of their tumors as determined by magnetic resona nce imaging and a pure-tone audiometry (PTA). The disparity between the thr eshold of PTA and the detective threshold of compound action potential (CAP ) or that of the cochlear microphonics (CM) was calculated. When the thresh old of the PTA was worse than the detective threshold of the CAP or the CM, the disparity was regarded as indicating a hearing loss of retrocochlear o rigin. Results: There was no correlation found between tumor size and the detectiv e threshold of CAP or CM. Disparity was found to correlate with tumor size. Conclusions: These findings seem to indicate that retrocochlear damage in A N increases parallel to the growth of the tumor and that retrocochlear dama ge can be detected by the ECoG before surgery.