[Clinical electrocochleographic study of widened AP-SP complex (broad wave)]

A clinical electrocochleographic study of 35 patients with cerebellopontine angle tumors and 49 patients with cochlear hearing losses was carried out using the transtympanic electrode technique. We defined a broad wave, of which the width of the AP-SP complex was more than 1.50 msec at 90 dBnHL stimuli using 4 kHz for one cycle click sound. We divided the waves into two types - an AP.SP mixed type and a dissociated type. Broad waves are not unique to retrocochlear hearing losses and are also seen in cases of severe high frequency hair cell damage whether cochlear or retrocochlear in origin. In cerebellopontine angle tumors, broad waves are not seen in cases with a typical retrocochlear pattern. We considered the dissociated type to have been broadened by severe high frequency hair cell damage in addition to the response at a lower frequency of about 1.5 to 4 kHz. We speculate that the broad wave, except in dissociated type, is caused by severe high frequency hair cell damage.