Contralateral routing of signals (CROS) hearing aids and the bone-anchored cochlear stimulator, or the Baha® system (Cochlear Americas, Centennial, CO), are standard treatments for unilateral hearing loss. Although each device has its advantages and disadvantages, Baha appears to be the preferred option due to better hearing quality and patient comfort, according to the physicians interviewed for this article.
CROS Indications and Contraindications
Traditional CROS consists of a microphone worn in the hearing-impaired ear and a receiver worn in the hearing ear. Sounds are then transmitted from the microphone to the hearing ear via a wire or wireless system.
CROS is indicated when a patient has one ear that-owing to high thresholds or poor speech discrimination-is not amenable to direct or air-conducting amplification, but whose opposite ear is still capable of hearing, said John K. Niparko, MD, George T. Nager Professor in the Department of Otolaryngology-Head and Neck Surgery at Johns Hopkins University in Baltimore.
One of the things that I find astounding is that close to 50,000 Bahas are in use worldwide, and just three years ago the number was under 10,000.
-John K. Niparko, MD
Contraindications for CROS include bad hearing in both ears and not being able to accommodate the microphone because of a closed ear canal or infection, said Darius Kohan, MD, Clinical Associate Professor in the Department of Otolaryngology at New York University School of Medicine. CROS is also difficult to use in patients who may have eczema in their ear canals, because the space around the microphone and receiver need to be clean.
A newer form of CROS, a transcranial system called TransEar® (TransEar, Johnson City, TN) consists of a small behind-the-ear digital hearing aid, which is joined by a thin flexible connector wire to a miniature oscillator that fits deeply and snuggly into the ear canal, according to manufacturer’s Web site (www.transear.com ).
The device sends sound vibration through the bony portion of the ear canal, through the bones of the skull to the inner ear or cochlea on the opposite side, explained Dr. Kohan.
One advantage of the transcranial CROS over the traditional CROS is that the patient does not need to wear a receiver in the good ear, said Jack Wazen, MD, of the Florida Ear and Sinus Center in Sarasota.
Baha Indications and Contraindications
The Baha consists of a sound processor attached to an external abutment, held in place by a titanium screw, which is surgically implanted into the skull behind the ear. The bone carries vibrations that bypass the external and middle ear and travel directly to the cochlear nerve.
The system confers sensitive hearing afforded by an efficient connection to the temporal bone, said Dr. Niparko. Because the cochlea is rigidly ensconced in the temporal bone, vibrations are faithfully conveyed to it, he explained.
Baha was originally indicated for hearing losses not amenable to conventional amplification, including mixed losses due to chronic infection, inoperable otosclerosis, and atresia of the ear canal or middle ear mechanism, said Dr. Niparko.
In these cases, the ear that has the hearing loss receives the Baha, explained Gail Murray, PhD, Director of Audiology Services and Clinical Director of the Cochlear Implant Program at the University Hospitals Case Medical Center in Cleveland, Ohio.
In 2002, the FDA approved Baha for use in patients with unilateral sensorineural hearing loss. Currently, the most common Baha indication is for patients with single-sided deafness who don’t benefit from a hearing aid on the side of impairment, noted Dr. Murray.
If, for example, a patient loses hearing in the left ear due to a brain tumor being removed or an infection, Baha can be implanted near the left ear and carry sound vibrations through the skull directly to the right ear’s cochlear nerve, explained Dr. Kohan. There’s no loss of energy of vibrations, he said. It’s an efficient way to transmit sound to the cochlea.
CROS Advantages
The advantage of traditional and transcranial CROS is that they both transmit sound from the bad ear to the good ear without requiring surgery, noted Dr. Kohan, adding that traditional CROS has been the workhorse of hearing aids for decades.
People who have contraindications for surgery might benefit from a CROS system, said Dr. Wazen. Although surgery for Baha is minimal, some patients prefer nonsurgical options, he said.
Another advantage of both traditional and transcranial CROS is that patients can remove these devices and use them when they want, said Dr. Kohan.
Baha Advantages
Although CROS doesn’t require surgery, Baha tends to have a high level of user satisfaction, said Dr. Niparko. Bone-conducted hearing seems to transfer sound across the skull in a narrow but useful band within the sound frequencies occupied by many consonants, he said. This creates a useful filter that appears to allow for access to speech sounds from the hearing-impaired side but limits noise inputs from that side, he explained.
Baha routes sound more efficiently, and the patient receives a clearer, stronger sound in the hearing impaired ear than with traditional or transcranial CROS, agreed Dr. Wazen. The device creates less distortion, resulting in a more pure and natural sound, he said.
One recent study (Otol Neurotol 2006; 27:172-82) of 23 patients with unilateral deafness conducted by Dr. Niparko and his colleagues found that Baha used for single-sided deafness provided greater benefits for patients than CROS. Advantages of Baha were related to averting the interference of speech signals delivered to the better ear, as occurs with conventional CROS amplification, while alleviating the negative head-shadow effects of unilateral deafness. Additionally, patients with moderate sensorineural hearing loss in the functioning ear had less trouble hearing background noise and experienced greater improvements in speech understanding when using a Baha.
In addition to sound quality, another advantage of Baha is that it doesn’t require an ear mold and can be worn off the ear, said Dr. Murray. It’s much more comfortable for patients and more easily disguised.
Patients also don’t have to worry about losing the device during physical activity because the titanium fixture becomes embedded in the bone, and the Baha snaps soundly to titanium abutment, she said.
From the perspective of my experience, patients are happiest with the Baha, said Dr. Murray, adding that most CROS patients come back to the office for other alternatives.
Dr. Wazen and his colleagues have also found that most patients prefer a Baha system over the traditional CROS. Most of the time we use the Baha, said Dr. Wazen. In a recent study (Otolaryngol Head Neck Surg. 2003;129:248-54), he and his colleagues studied 30 patients who received a CROS hearing aid for a one-month period and then switched to the Baha system. Patients reported a significant improvement in speech intelligibility in noise, greater improvement in perceived benefit, increased satisfaction, and better quality of life with Baha than with CROS.
While Baha generally provides the best hearing of the three options, patients should understand the post behind the ear that holds the device in place can be difficult to maintain.
-Darius Kohan, MD
Cost can also be a factor for patients when choosing Baha. Because the Baha interfacing components are surgically placed, the device is generally covered by insurance, said Dr. Murray. The price of the Baha will vary by center, she said, but the current cost is roughly $10,000, excluding the associated operative costs.
However, coverage for children is not available until they are five years of age, because their skulls are usually too thin for a surgically implanted system prior to that time. Until then, they may use a soft headband to hold the Baha in place.
Overall, the Baha system is one of the fastest growing technologies in otolaryngology, noted Dr. Niparko. One of the things that I find astounding is that close to 50,000 Bahas are in use worldwide, and just three years ago the number was under 10,000, he said.
CROS Disadvantages
For both traditional and transcranial CROS, you don’t find much user satisfaction, said Dr. Niparko.
Both systems require that a device be placed in the ear canal of the better-hearing ear, which the vast majority of users find to be a drawback, he said. As this better ear is the lifeline to the world of sound for the monaural patient, any type of impediment to hearing on that side is noticeable and often distressing, explained Dr. Niparko.
Patients can experience a blocking sensation with sound because of having to wear a device in their good ear, agreed Sam J. Marzo, MD, Associate Professor in the Department of Otolaryngology at Loyola University Health System in Maywood, IL, and a consultant for Cochlear Corporation. Dr. Marzo often sees patients who have tried CROS hearing aids but who are unhappy with the technology for this reason.
Moreover, because transcranial CROS must fit deeply and tightly within the ear canal, patients may experience discomfort, pain, and problems with cerumen buildup or infection, said Dr. Wazen.
Dr. Murray and her colleagues generally don’t use transcranial CROS for this reason. It’s also twice as expensive as a traditional CROS device, and neither the traditional or transcranial CROS is covered by most insurance companies, she said. Prices vary greatly from center to center. We charge $3500 for a CROS system and $4700 for a transcranial CROS, she said.
Baha Disadvantages
Although CROS may be uncomfortable, having to undergo surgery is the main drawback of Baha. The chief concern with the bone-anchored system is the need for a bony implant that connects to the processor through the skin, said Dr. Niparko. However, with careful surgical planning, the implant can be placed in a manner that makes it unobtrusive and a useful conduit of sound, he added.
Additionally, patients may experience infection around the external abutment. I tell patients they have to take care of the post like they take care of their teeth, said Dr. Wazen. They need to clean and brush it and remove any crusting that occurs so it will last a lifetime without major problems, he explained. If patients are not careful, the surrounding skin can become inflamed and infected. Most of these problems can be treated by a topical antibiotic or, in some cases, an oral antibiotic, he said.
Some people come in to the clinic thinking they are Baha or CROS candidates, but what they consider to be their good ear actually has bad hearing. These patients may need a cochlear implant.
-Sam J. Marzo, MD
Good surgical implantation can also help patients avoid infection, said Dr. Niparko. A lot of surgeons have learned to more adequately thin the skin surrounding the implant to help decrease the risk of infection, he said.
Additionally, some teenagers don’t like the aesthetics of Baha, said Dr. Murray. They have commented that the Baha abutment looks like Frankenstein, which can be viewed as an extreme reaction, but you have to understand where the patient is coming from, she said. The attachment is permanent and penetrates the skull.
What Patients Should Know
Patients who have deafness should know there are solutions and technologies available to help them hear, said Dr. Wazen.
All three options-CROS, transcranial CROS, and Baha-can be advantageous, added Dr. Kohan.
Physicians should provide patients with all the pros and cons of various hearing aids in as nonbiased a fashion as possible, said Dr. Murray.
Generally, patients should understand that even though CROS is the workhorse of hearing aids and doesn’t need surgery, the technology is outdated, said Dr. Kohan. Fewer patients are using CROS, and smaller numbers of audiologists know how to maintain it, he said.
The transcranial CROS hearing aid has replaced traditional CROS for people who don’t want surgery, added Dr. Kohan. And while Baha generally provides the best hearing of the three options, patients should understand the post behind the ear that holds the device in place can be difficult to maintain.
Patients need to understand that to use any of these options for unilateral hearing loss, they need to have good hearing in at least one ear, said Dr. Marzo. Some people come in to the clinic thinking they are Baha or CROS candidates, but what they consider to be their good ear actually has bad hearing, he explained. These patients may need a cochlear implant.
On the Horizon
Even as Baha and CROS may help patients with unilateral hearing loss, physicians and researchers hope technological improvements will provide patients with more treatment options.
Hearing aids implanted in the middle ear that could help with unilateral hearing loss are currently being studied in clinical trials, said Dr. Wazen.
The hope is that we could develop a system that can simulate Baha but that doesn’t require an implant that comes through the skin, said Dr. Niparko. But we haven’t found an efficient way to do that yet.
The Vibrant Soundbridge® (Vibrant Med-El, Innsbruck, Austria) is a device currently approved to treat sensorineural, conductive, and mixed hearing loss in Europe, and could offer patients in the United States another option if eventually approved by the FDA, said Dr. Kohan.
According to company literature, the Vibrant Soundbridge is a semi-implantable hearing aid that leaves the ear canal open. An audio processor is held to the back of the head behind the ear with a magnet and processes sounds into electrical signals, which are transcutaneously transmitted to an implanted device that causes the ossicles to vibrate. Some experimental protocols have been performed in the United States, but the FDA has not yet approved it for use here.
Researchers are also investigating the delivery of intratympanic steroid injections to the inner ear to help prevent sensorineural hearing loss. We believe this reduces inflammation, said Dr. Marzo. Some of the hair cells are in a state of shock, and steroids seem to help.
Cochlear implantation for single-sided deafness is another area of ongoing research, said Dr. Marzo. Investigators don’t know how the implant is going to interact with hearing in the good ear, he said. That’s something that is undergoing further investigation.
©2009 The Triological Society