Each year in the United Sates, an estimated 60,000 people will experience a complete loss of hearing in one ear, a condition known as Single Sided Deafness (SSD). Many of these cases are simply unexplained, and are the result of medical conditions and factors not yet understood. Some of these individuals will regain their hearing at a later date. Again, for unknown reasons, their condition reverts to its normal healthy state, and they are spared the considerable lifetime hurdle of coping with hearing in only one ear.
For other individuals, the diagnosis of an acoustic neuroma is very frequently an entry into the world of SSD, and there is certainly no hope that the hearing loss will spontaneously correct itself. The Acoustic Neuroma Association, Cumming, Ga, estimates that 2,000 to 3,000 individuals per year in the United States are diagnosed with this disease state. Removal of the neuroma, or the neuroma itself, in more than 50% of cases causes severe trauma to the auditory nerve, and although the patient is spared the sometimes life-threatening effects of the benign tumor, the postoperative results may be a total hearing loss in one ear.
The Prospect of a Lifetime with SSD
Amy Pack, president and publisher of three local California newspapers, was attending a professional conference in Washington, DC when she first learned that all was not right with her hearing. An interview on stage had just begun, and she found it very difficult to understand the conversation. She looked at the people around her, noticing that she was the only person in the audience who seemed to be concerned. She put one hand over her right ear, then the left—that was the moment when she understood she had a serious problem.
“Most of my hearing in my right ear was gone, replaced with a constant and loud mix of chirping, bonging, and screeching,” she recalls. The subsequent removal of a neuroma and the difficult recovery period occupied the better part of 2 years. Six days after the procedure, she was sent home. “The medium-sized tumor had filled the inner ear, surrounding the balance and hearing nerves. That explained the hearing loss,” she says. Although surgery successfully removed the tumor, Amy was left to cope with the ongoing and frustrating prospect of a lifetime with SSD.
“One of the most unfortunate aspects of having hearing in only one ear is that it is not generally recognized as the severe disability that it actually is,” Amy says, adding that she was overcoming the dual issues that often affect acoustic neuroma patients: balance and hearing loss. Facial paralysis can also result from the procedure, although in Amy’s case she was not so afflicted. “People would greet me from different directions, but I couldn’t tell where their voices were coming from. I was often disoriented, and had no idea that returning to a routine work and home life would be so tiring and difficult.”
As with most individuals who suffer from SSD, Amy was able to function by learning to compensate and slowly adapting to minimize the effects of the condition. She would position herself in groups or when talking to individuals so that her good ear “faced” the conversation. But in many situations, it was impossible to function normally, such as noisy restaurants, or while driving in a car; unless a passenger spoke in an abnormally loud voice, she could simply not understand what was being said.
The Professional Approach
SSD presents a difficult case to medical professionals as well. Normal hearing aids would provide no benefit whatsoever to Amy’s condition, as simply amplifying the sound in her bad ear would not overcome her complete sensorineural loss caused by the dysfunctional auditory nerve. Other treatments, such as implants into the cochlea, could overcome deficiencies in that structure, if there were any, but again, her cochlea was not the issue. The auditory nerve, damaged or destroyed by the neuroma and its removal, was the issue, and no current medical technology or techniques exist to repair it in such a state.
CROS aids—the contralateral routing of signal—have been an option for treating SSD for many years. This system generally involves the wearing of two devices—one on each ear—and is not widely regarded by patients as a satisfactory option due to the device’s bulkiness and the fact that the “good” ear is often partially obscured due to the presence of an ear mold so that sounds can be transferred from the bad ear into the hearing ear.
In sum, professionals have been left with an arsenal of treatments that are not particularly appropriate, effective, or acceptable to patients with SSD. Hence, the common refrain that patients such as Amy have had to adjust to: I’m sorry, there’s nothing else I can offer for your hearing problem.
Bone Conduction: A New Treatment for SSD
In 2004 the Food and Drug Administration (FDA) cleared a new treatment application of the Baha system by Denver-based Cochlear Americas for SSD. Amy was one of the few people who received the device prior to its clearance by the FDA, in a clinical study to observe its effectiveness in treating SSD. The year was 2001. She had been living with SSD for 24 months and was trying to “close that chapter” of her life. “I was continually frustrated with my hearing loss, but my feeling at the time was moving toward acceptance. I felt that my problem with hearing was just going to be something I had to live with for the rest of my life,” she says. Amy had not been presented with any viable alternatives. She received an offer to participate in the device study, and when she saw that there was little—if any—downside risk, she says she jumped at the opportunity to try a new treatment.
The study involved testing two hearing devices for SSD, a CROS aid and a device that worked on the principle of bone conduction. Bone conduction was first reportedly used when biophysicist Georg von Bekesy demonstrated that air and bone conduction stimulation produced identical response to cochlear receptors. The Baha system, in use in Europe since 1980, transmits sound from a sound processor, through a titanium abutment and implant, and then directly into the recipient’s skull. The Baha system is the only implantable device to effectively treat hearing loss through this principle.
Simply stated, bone conduction achieves sound perception when the skull bone is vibrated. In Amy’s case, the vibratory energy would cross from her “bad” side through her skull and cause the cochlea on the other side of her head to perceive the sound. Thus, the treatment was intended to allow her to hear from both directions effectively for the first time since she developed SSD.
Amy had tried the Baha with a tester kit, and immediately recognized its superiority over the hearing aid. The sound processor can be fitted with an acrylic conduction rod called a test rod or a test headband to demonstrate the device. To test the Baha’s effectiveness, the rod with the Baha sound processor attached can be held tightly against the forehead or, for a more realistic and stronger effect, can be placed in the mouth so that when the patient bites down, the teeth conduct sound into the skull. The test headband is fit in a similar fashion as more conventional bone conduction hearing aids, where a flexible steel rod is placed over the head and an adaptor with the Baha sound processor is attached and placed on the mastoid process of the deaf side. Testing the Baha against the forehead is also effective, but because sound vibrations must first transfer through skin and subcutaneous tissue before reaching the bone, the sound quality and intensity are reduced.
The Procedure and Outcome
After a patient has recovered from an acoustic neuroma, they are sometimes reticent to go “under the knife” again, so traumatic is the experience. In Amy’s case, the thought of having a doctor operate again was an emotional decision, but the prospect of having hearing “returned” to that side absolutely outweighed any hesitations.
The surgical procedure is performed under local anesthetic and takes less than 1 hour. “The surgery was quick and I was awake during the entire procedure,” she says. Behind her right bad ear, a small skin flap was created, and some subcutaneous material removed. Then, a hole was drilled into the bone, a self-tapping titanium implant was screwed in, and the skin flap folded back over the site—the small titanium abutment cresting the surface by a few millimeters.
A critical aspect of the procedure then takes place. Over the next 3 months or more, depending on the age of the patient and the quality of the bone, the bone surrounding the implant osseointegrates with the titanium. This provides an excellent conductive bond with the implant so that sound transfers efficiently from the implant to the bone to the cochlea. Additionally, the implant simply becomes part of the recipient; it is secure and easily cared for postoperatively.
The final stage is when the sound processor is fitted. This is a small unit, about the size of the last segment of a person’s thumb, and is nearly unnoticeable, particularly when fitted and color-matched to a person with long hair. The processor is digital, and has adjustments for automatic gain control, frequency, and volume, and a directional microphone. It simply snaps on and off, and is maintenance-free, with the exception of the batteries, which last a week or more.
Amy’s experience demonstrated the benefit of the device and clearly validates the principle of bone conduction in treating SSD. Although her hardships and recovery from the acoustic neuroma were life-changing, the Baha was able to greatly assuage a lifetime with hearing loss. Before the Baha, she could not communicate in crowded or noisy environments such as restaurants, and now when she drives in her car, there is no need for the passenger to shout to be heard. “My ability to identify directional sound has improved about 75%—prior to the Baha, it was virtually zero, and the sound is crisp and clear,” she says. “It has made an considerable difference in the quality of my life.”
Teri Sinopoli, MA, CCC-A, is an audiologist with more than 25 years’ experience in the hearing health care profession. She is currently Clinical Director of Bone Anchored Solutions, a unit of Cochlear Americas, Denver.
