In the drawing above, sound is entering the bone-anchored device fitted on the deaf, right side (seen on the left side of the drawing with a red X over the non-functioning cochlea). Bone-conducted sound travels to both ears, but only the functioning left ear, in this case, perceives the sound. Bone-conduction sound travels nearly the same speed as through air, so bone-conduction sound is a very efficient way for sound to travel. Everyone’s bone conduction is different. Therefore, the hearing device that is fitted to the individual is “tuned” to that person’s bone-conduction. A traditional hearing aid is recommended for the better hearing ear if the better hearing ear has a mild to moderate hearing loss. If the better hearing ear has a severe loss, then bone-anchored devices are generally not recommended. For more information about bone-anchored hearing devices, please click here.
Although there are several benefits of the CROS/BICROS systems and the bone-anchored devices for SSD, these systems do not improve tinnitus (ear noise) and, in general, do not help with sound localization. The CROS/BICROS and bone-anchored systems provide “pseudo” or “simulated” hearing on the deaf side. Therefore, individuals fitted with these devices are only hearing from one ear; hearing function in the deaf ear is not restored.
Currently, hearing restoration can only be performed with a cochlear implant. Cochlear Implants electrically stimulate the auditory nerve directly. (For more information regarding cochlear implants, please click here.) In the last few years, cochlear implants have been used to restore hearing function to the deaf ear in some cases of single-sided deafness.
Cochlear implants have had a multi-decade history of use in the world. Since the 1980’s in the United States, cochlear implants have been an accepted medical/surgical treatment of severe-to-profound bilateral sensorineural hearing loss. In 2008, physicians from Belgium published a study regarding cochlear implantation for patients with severe unilateral tinnitus and single-sided deafness (1). The goal of the study was to treat the patients’ severe tinnitus; all other previous treatments for the patients’ tinnitus were unsuccessful. Ninety-five percent of the patients had a significant reduction in tinnitus severity. In a follow-up study published in 2009, the same group of patients was found to have improved hearing using the cochlear implant for single-sided deafness (2). Since then, numerous studies have reported the benefits of cochlear implantation for single-sided deafness. These studies indicate improved speech understanding in noise (3), and improved sound localization (4). These findings are not surprising considering that two functioning ears are necessary for proper noise suppression and sound localization. Other studies continue to show a reduction in the intensity of tinnitus when the cochlear implant is in use (5). In one study of eleven adults with SSD, the researchers compared the results of using a CROS, a simulated bone anchored device (by resting the bone conduction device on the skin, rather than surgically implanting the bone-anchored portion of the system), and a cochlear implant for SSD (6). This study concluded that the cochlear implant was superior to the CROS and bone-conduction treatment options (as used in this study) for SSD. The researchers also found that the cochlear implant did not interfere with hearing speech in the normal hearing ear, which was a concern before the 2008 Belgium study. In another study of 48 adults with a cochlear implant for SSD, the researchers found many of the subjects were able to hear fairly well when the only the cochlear implant side was used for hearing (3).
Although a cochlear implant appears to be a promising treatment for single-sided deafness, the cochlear implant cannot be used in all cases of single-sided deafness. A functioning cochlear nerve must be present for a cochlear implant to restore hearing. In many cases of surgically treated acoustic neuromas, the cochlear nerve has been removed to ensure complete tumor removal. In these cases of surgically treated acoustic neuromas, a cochlear implant is not an option. If the cochlear nerve has been preserved, however, a cochlear implant may be an option for SSD after surgical treatment of an acoustic neuroma. Finally, a cochlear implant is an option for SSD in cases of acoustic neuroma treated with radiosurgery (7). The cochlear nerve is preserved anatomically in cases of radiosurgery. Bibliography
1. Van de Heyning P, Vermeire K, Diebl M, Nopp P, Anderson I, De Ridder D. Incapacitating unilateral tinnitus in single-sided deafness treated by cochlear implantation. Ann Otol Rhinol Laryngol 2008; 117:645-652.
2. Vermeire K, Van de Heyning P. Binaural hearing after cochlear implantation in subjects with unilateral sensorineural deafness and tinnitus. Audiol Neurootol 2009; 14:163-171.
3. Finke M, Strauss-Schier A, Kludt E, Buchner A, Illg A. Speech intelligibility and subjective benefit in single-sided deaf adults after cochlear implantation. Hear Res 2017; 348:112-119.
4. Grossmann W, Brill S, Moeltner A, Mlynski R, Hagen R, Radeloff A. Cochlear Implantation Improves Spatial Release From Masking and Restores Localization Abilities in Single-sided Deaf Patients. Otol Neurotol 2016; 37:658-664.
5. Arts RA, George EL, Stokroos RJ, Vermeire K. Review: cochlear implants as a treatment of tinnitus in single-sided deafness. Curr Opin Otolaryngol Head Neck Surg 2012; 20:398-403.
6. Arndt S, Aschendorff A, Laszig Ret al. Comparison of pseudobinaural hearing to real binaural hearing rehabilitation after cochlear implantation in patients with unilateral deafness and tinnitus. Otol Neurotol 2011; 32:39-47.
7. Amoodi HA, Makki FM, Cavanagh J, Maessen H, Bance M. Cochlear implant rehabilitation for patients with vestibular schwannoma: report of two cases. Cochlear implants international 2012; 13:124-127.