Electrocochleographic evaluation of hearing loss in acoustic neuromas

We enrolled thirty-four patients diagnosed as having acoustic neuromas (AN) by MR imaging between 1988 and 1995. We made a comparison between the patients' ECoG findings and the size of their tumors determined by MR imaging, and a pure tone audiogram (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. There was no correlation found between tumor size and the detective threshold of CAP or CM. Disparity was found to correlate with turner size.