Round window versus promontory stimulation: assessment for cochlear implant candidacy

If the cochlea, the hearing organ, is destroyed and segments of the auditory nerve (the sensory nerve associated with hearing) remain, cochlear implants may provide at least some hearing. The cochlear implant is an electrode system that is inserted into the bony cochlea of the ear; it requires electrical signals for stimulation. In many clinics the ability of the patient's nervous system to respond to cochlear stimulation is tested by direct electrical stimulation of the inner ear. One method is to place a small electrode on bone overlying the basal turn of the cochlea (the promontory, or portion of the cochlea that detects high frequency). This may be done through a small incision in the ear drum, or more recently, by simple perforation the ear drum with a small needle electrode, which is then brought into contact with the promontory. This paper discusses the use of a small ball-shaped electrode that is placed on the round window membrane, a thin partition enclosing a fluid-filled cavity of the inner ear (the perilymphatic space). Although this procedure uses slightly low-voltages to stimulate the inner ear, compared with the promontory electrode, the results were not significantly different. The use of a transtympanic needle electrode is less traumatic and the procedure is easier to perform. (Consumer Summary produced by Reliance Medical Information, Inc.)