Measurement of endocochlear DC potentials in ears with acoustic neuromas: a preliminary report

The pathogenesis of hearing loss in acoustic neuromas remains to be elucidated. To obtain more detailed information about inner ear damage in this disease, especially that dealing with the possibility of ischemia of the inner ear due to compression of the blood supply in the internal auditory canal by acoustic neuromas, measurement of endocochlear DC potential (EP) was attempted in three ears with acoustic neuromas during surgical removal of the tumors by the translabyrinthine approach. The size of each tumor was 3.0, 0.8, and 1.8 cm, respectively. An EP with a positive value was recorded in each of the three ears, i.e., 54, 57, and 38 mV, respectively, although the first and third patients were profoundly deaf on the side with a tumor. These findings were interpreted as being evidence of retention of function by the stria vascularis and the existence of blood supply to the inner ear in spite of the presence of tumors. Measurement of the EP seems to provide a new tool with which to analyze the causes of hearing loss in acoustic neuromas. Relatively low EP values may suggest mild dysfunction of the stria vascularis with acoustic neuromas.