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 electrocochleograph (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 resonance imaging and a pure-tone audiometry (PTA). The disparity between the threshold of PTA and the detective threshold of compound action potential (CAP) or that of the cochlear microphonics (CM) was calculated. When the threshold 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 origin.

RESULTS

There was no correlation found between tumor size and the detective threshold of CAP or CM. Disparity was found to correlate with tumor size.

CONCLUSIONS

These findings seem to indicate that retrocochlear damage in AN increases parallel to the growth of the tumor and that retrocochlear damage can be detected by the ECoG before surgery.