Regarding cochlear implantation, what are the criteria for determining which ear to implant -- from a surgeon's viewpoint?
There are several criteria in determining which ear to implant. In essence, there are audiometric and anatomic considerations. Both are important, and both must be considered when determining which side to implant.
From an anatomic standpoint, the shape and size of the cochlea must be considered. Congenital abnormalities of the cochlea may preclude one side from being implanted. If the cochlea was normally formed, there are conditions that can lead to ossification, or even closure, of the cochlear canal. For example, meningitis can cause ossification within the first year after deafness. Additionally, otosclerosis may cause narrowing of the cochlear duct.
The size of the mastoid is also important in determining which side to implant from the anatomic perspective. The side that has more pneumatization (or mastoid air cells) may be selected as it would be easier to implant. The location of the facial nerve must also be considered -- especially in congenitally deafened ears. In most post-lingual deafness, the facial nerve is in the normal anatomical position but a facial recess approach opening bone between the facial nerve and chorda tympani nerve in the middle ear space must be performed for cochlear implantation. This area must be accessible from a surgeon's perspective. A history of chronic otitis media occasionally occurs with cochlear implant patients and this too, may present challenges and must be considered when selecting a side.
The audiometric criteria includes length of deafness (the ear that most recently lost hearing is generally implanted), degree of hearing loss and the ability to function with hearing aids.
Other issues which impact which side to implant will include etiology of hearing loss. For example, if the patient lost the hearing in the left ear due to Meniere's disease and the right ear hearing loss was due to an acoustic neuroma, removed via a translabyrinhine approach, the left ear is the only candidare for cochlear implantation.
Additionally, the surgeon also considers the patient's personal preferences. Some patients prefer to have one side implanted for their own reasons. For example, they sleep on the one side, handedness, they think one ear is better or worse etc. These issues are also considered by the surgeon, and they too, may impact the selection of left versus right.
William H. Slattery III, M.D.
House Ear Clinic, Inc.
Associate, House Ear Clinic, Inc.
Director, Clinical Studies Department, House Ear Institute
Clinical Professor, University of Southern California
2100 West Third Street
Los Angeles, California 90057-1922