Simultaneous comparison between transtympanic and extratympanic electrocochleography

Electrocochleography (ECoG) has become a mainstay in the diagnostic armamentarium used by otolaryngologists and audiologists in the evaluation of patients suffering auditory and vestibular symptoms. Controversy exists, however, regarding the relative accuracy of ECoG when recorded with a non-invasive external auditory canal (EAC) electrode as compared to that recorded using a transtympanic electrode. In an effort to resolve this controversy, 19 healthy volunteers (37 ears) with no history of otologic disease or symptoms and a normal screening pure-tone audiogram were studied. For each volunteer, a transtympanic electrode was placed on the cochlear promontory bilaterally under iontophoretic anesthesia followed by the immediate placement of an EAC TIPtrode (Etymotic Research Laboratory, Elk Grove Village, Illinois). Signals from both the transtympanic electrode and the TIPtrode were recorded simultaneously following click stimulus using the Nicolet CA 1,000. Preliminary analysis of these recordings identify no significant difference in summating potential/action potential ratios between EAC and transtympanic electrodes in this normal subject population.