Complete, unilateral hearing loss or single-sided deafness (SSD), is most commonly caused by acoustic tumors, sudden sensorineural hearing loss, Meniere’s disease, chronic ear disease and head trauma.
Single-sided deafness can cause a host of problems, besides simply not hearing on one side. These problems include:

• Difficulty determine the direction of sound
• Inability to separate background noise from conversational speech
• Fatigue: Listening with only one ear is physically tiring and stressful.

For those who have not experienced single-sided deafness, it is difficult to appreciate the handicaps that occur, and the lifestyle changes needed, for those with this type of hearing loss. Some individuals learn to live with a unilateral hearing loss. Others, however, must make significant life changes as they are unable to cope with everyday environments, such as business meetings, busy restaurants or family gatherings.

Hearing Device Options for Single-Sided Deafness

A traditional hearing aid is not an option for SSD. A traditional hearing aid amplifies sound. A person with SSD would not hear the amplified sound directed into the deaf ear. At best, the amplified sound would be heard as distortion.
Rather than a traditional hearing aid, a CROS or BICROS hearing aid system is one treatment option for SSD. CROS is the acronym, Contralateral (meaning opposite side) Routing of Off-side Signal. BICROS is bilateral routing of the off-side signal. In a CROS configuration, a microphone/transmitter device is placed in the SSD ear (the microphone/transmitter device is housed in what appears to be a traditional hearing aid). The signal that is picked up by the microphone is routed (wirelessly) to a device that also looks like a traditional hearing aid on the good or better hearing side. A BICROS system is for someone with SSD and a hearing loss in the better hearing side. A BICROS system works the same as a CROS, but the device on the hearing side is truly a traditional hearing aid that also has the capability of picking up the sound from the device on the deaf side. In summary, in the CROS and BICROS systems, the sound that is heard at the SSD ear is routed to the other, good or better, hearing ear.
The early CROS devices in the 1960s were incorporated into eyeglasses, which was a common practice for hearing aid fitting during that decade. The eyeglass version evolved into bilateral ear-worn devices connected by a wire behind the head. With current generation CROS and BICROS systems, the two ear-worn devices are connected by wireless technology.
There are now several hearing aid companies that produce wireless CROS and BICROS devices.

Bone-Anchored Options

Bone-anchored hearing devices are another option for treatment of single-sided deafness. Similar to the CROS system, the bone-anchored device directs sound to the opposite, contralateral hearing side. Rather than send the sound wirelessly to the other side as in the CROS system, bone-conduction devices transmit sound through the bones of the skull. The way bone-anchored hearing devices transmit sound to the opposite side of the skull is shown graphically in the drawing below.

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.

Cochlear Implants

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.