From the Desk of Gus Mueller
In clinical audiology, there are many areas that require extensive background knowledge, and keen skills in testing technique and procedures, as they deal with patients we encounter on a regular basis. There are other topics related to clinical audiologic practice that we need to know about, even though we may go years, or even a career, without seeing a patient that falls into this category. Our 20Q topic this month relates to the latter.
The first auditory brainstem implant (ABI) was performed in 1979 at the House Ear Institute. This type of implant originally was developed for adults who developed neurofibromatosis type 2, and who could not use hearing aids or traditional cochlear implants effectively. More recently, ABIs have been used with children; in the U.S., the FDA approved clinical trials of ABIs for children in 2013. With children, candidacy often relates to congenital cochlear and/or nerve VIII anomalies.
There are only a handful of audiologists who work with ABI patients, and we are fortunate to have one of them with us this month at 20Q. William H. Shapiro, AuD, saw his first ABI patient in the late 1990s, and has worked with over 60 since then, including many pediatric cases. He is Clinical Assistant Professor of Hearing Health, in the Department of Otolaryngology at the New York University. He also holds the positions of Director of Family Group Audiology, and the Supervising Audiologist of the Cochlear Implant Center.
Dr. Shapiro has been at NYU for over 30 years, not straying very far from his Brooklyn roots. He has an impressive list of publications related to both cochlear implants and ABIs, going back to clinical trials with cochlear implants in the early 1980s. He serves on the advisory board of two cochlear implant manufacturers. In 2008, Bill was the recipient of the “Outstanding Clinician Award” from the New York State Speech, Language and Hearing Association.
While your encounters with ABI candidates may be few, this article will serve as a great overview and go-to resource on the subject matter. In this 20Q, Dr. Shapiro provides an excellent discussion of the ABI history, the clinical protocols, and the emerging work with the pediatric population.
Gus Mueller, PhD
To browse the complete collection of 20Q with Gus Mueller CEU articles, please visit www.audiologyonline.com/20Q
20Q: Auditory Brainstem Implants - Continued Advancements for Both Adults and Children
- Readers will be able to define an auditory brainstem implant (ABI) and explain the difference between an ABI and a cochlear implant.
- Readers will be able to describe candidacy for an ABI.
- Readers will be able to describe the role of audiologists in determining ABI candidacy, with pre-operative tasks and their post-operative responsibilities.
- Readers will be able to discuss the variable outcomes for people who receive an ABI and some of the factors impacting outcomes.
1. Auditory brainstem implant? Isn't that just another name for a special kind of a cochlear implant?
No, not at all. Auditory brainstem implants (ABI) are actually are quite different. A cochlear implant (CI) is indicated for individuals with cochlear damage, either due to missing hair cells or a malformed cochlea, which results in a sensory loss. The internal component of the CI is comprised of an electrode array and a receiver stimulator. The array is threaded into the scala tympani of the cochlea, which takes advantage of the tonotopic organization of the cochlea and in turn, stimulates the viable auditory nerve directly. For approximately 98% of patients diagnosed with a moderately severe-to-profound sensorineural hearing loss, the loss is actually sensory. In this cases, a cochlear implant may be the indicated treatment. However, individuals with neural involvement are typically not good candidates for cochlear implants. The auditory brainstem implant, like the CI, is comprised of a receiver stimulator, but instead of an electrode array, an electrode paddle is placed in the brainstem on the surface of the cochlear nucleus.
2. Have ABIs been around for a while?
The auditory brainstem implant was first developed in 1979 by William F. House, MD, a neuro-otologist associated with the House Ear Institute, for patients with neurofibromatosis type 2 (NF2). This original ABI consisted of two ball electrodes that were implanted near the surface of the cochlear nucleus. In 1997, Robert Behr at the University of Wurzburg, Germany performed the first MED EL Combi 40+ ABI implantation using a 12-electrode array implant with a speech processor based on the C40+ cochlear implant (Jackson, Mark, Helms, Mueller, & Behr, 2002). In 1999, Vittorio Colletti from Verona, Italy performed the first pediatric ABI (Colletti, Fiorino, Sacchetto, Mioretto, & Carner, 2001).
So, yes, they have been around for a few decades. The Cochlear Corporation ABI 24M received FDA approval in 2000 for individuals twelve years of age and older with NF2 and is the only FDA approved device at this point. Newer devices are currently being studied.
3. You mention NF2?
Yes, NF2 is a rare genetic disorder that is similar to NF1 in that it involves tumors along the various cranial nerves. In NF2 there are not as many physical signs of the disease. Unlike NF1, patients with NF2 may have only a few cafe au lait spots, Lisch nodules or bony deformities. These patients usually suffer from benign tumors (neuromas and schwannomas), which can affect hearing or balance. In addition, these patients can have other types of tumors (gliomas and meningiomas), that can occur anywhere in the body. For individuals who require removal of the acoustic neuromas due to worsening symptoms, the possibility exists that due to the surgical approach the auditory nerve will be sacrificed, causing deafness. Hence the ABI would be placed on the surface of the cochlear nucleus after tumor removal and the patient would be stimulated, with an external speech processor, 4-6 weeks after surgery.
4. What type of patient is an appropriate candidate for an ABI?
According to FDA regulations, only adults with NF2 are approved candidates for an auditory brainstem implant; however, they have been performed on pediatric patients for years in European countries. In the US, a handful of medical centers are undergoing FDA approved feasibility studies in the pediatric population.
Criteria for selection for our research here at New York University (NYU) is the following:
- Age 18 months to 21 years
- Two groups - 18 months to 5 years; up to 21 years (post-lingual group)
- Bilateral profound sensorineural hearing loss documented on physiologic and behavioral assessment
- No cochlea or cochlear nerve hypoplasia/aplasia
- Inability to place a CI due to fibrous growth from previous CI
- Meningitis with no benefit from CI
- Strong family support
- English language competency in guardians
- Reasonable expectations of family
- Understand that child may not develop oral language
Exclusion criteria include:
- Medical contraindications
- Cognitive or developmental delays that could interfere progress/performance
- Anomaly or pathology of brainstem or cortex
- NF2 or other brainstem or cranial nerve tumors
- Psychological contraindication
5. Can you tell me a little about the surgery and placement of the ABI?
For individuals with NF2, the surgeon will spend a significant amount of time removing the acoustic neuroma. Depending upon the surgical approach, it may involve sacrificing the auditory nerve, thus rendering the patient deaf. Following the tumor removal, the electrode paddle is inserted through the 4th ventricle onto the surface of the cochlear nucleus. For pediatric ABI’s, as there is no tumor removal, the surgery is much quicker and the post-op stay is also shorter.
6. Is the post-op recovery for ABI surgery about the same as a CI surgery?
The ABI placement requires a craniotomy; it is brain surgery whereas a CI is inner ear surgery. The post-op hospital stay is a few days longer for pediatric ABI as compared to CI surgery. For NF2 adults, the post-op stay is even longer as these patients have undergone tumor removal as well.
7. Do all surgeons who implant CI also implant ABI?
No. ABI surgery requires different team members and a different surgical approach that may not be familiar to CI surgeons.
8. Who should be included on the ABI team?
The ABI team should be an experienced multi-disciplinary team including otology, neurosurgery, electrophysiology, audiology, and speech-language pathology. The surgical team members should have extensive surgical experience with either the translabyrinthine or retrosigmoid route.The electrophysiologic team members are responsible for monitoring of cranial nerves Vth, VIIth, VIIIth (EABR), IXth, Xth, XIth. The team should have a cochlear implant program experienced in advanced programming, as well as a speech-language pathologist with experience working with this population.
9. What is the pre-op work-up for pediatric ABI surgery?
Imaging is critical in determining the integrity of the cochlea, auditory nerve, and other surrounding structures. Although a CT scan is standard protocol for all cochlear implants, in the ABI work-up, the surgeon will also want to obtain an MRI to visualize soft tissue anatomy, i.e. the auditory nerve. Behavioral testing continues to be the gold standard in the audiologic assessment. In fact, if the audiologist can demonstrate hearing ability on audiometric testing, even if the auditory nerve cannot be visualized on imaging, the team will consider a CI as the first treatment. It is possible that the nerve is “hiding,” especially in a challenging anatomic case. The communication evaluation is important to assess the child’s language development, communication style, etc. Physiologic testing such as ABR, ASSR, and OAE are valuable tools to assess the auditory pathway integrity in the pediatric population.
Finally, an eABR via promontory stimulation may be employed. This is a procedure that is not commonly available and certainly not widespread but can provide valuable information about the auditory nerve. This procedure was originally described by Paul Kileny from the University of Michigan and has been modified at our research lab at the NYU School of Medicine. It involves placing a needle electrode through the eardrum on the promontory of the middle ear and stimulating the anesthetized child with an electrical current at various frequencies/amplitudes. This is done in an attempt to generate a response that is captured by a commercially available ABR. This procedure, although still in the early stages, has been successful in assessing auditory nerve integrity and therefore assisting the team in pre-operative decision-making (CI vs. ABI).
10. What about parental expectations in pediatric ABI’s?
This is an important issue. Often ABI’s can be a last resort for children whose parents want to pursue auditory communication for their child. This treatment, however, with the current technology, rarely provides enough auditory information for a total auditory approach. Parents are counseled extensively about additional communication modalities available to the child, such as the use of sign language, as the ultimate goal is to facilitate language with children. These are typically difficult conversations to have with parents who so desperately want their child to have completely aural/oral speech and language. Ongoing counseling is generally required.
11. Other than the audiologic assessment that you mentioned, does the audiologist have other responsibilities in the overall ABI process?
Absolutely. The audiologist is present during the actual surgery to monitor and ensure optimum placement of the device. We use the manufacturer’s custom software to present a biphasic stimulus on various electrode pairs on the electrode paddle placed in the cochlear nucleus. Currently, we use ABR to read a biphasic time-locked response whose first wave occurs between 1.2-1.7 msec. Additionally, via electrophysiologic responses, the audiologist can differentiate between any untoward stimulation, such as non-auditory side effects (NASE) and auditory responses. It is important to note that the area of stimulation is neurologically congested and the possibility exists of irritation of other cranial nerves in the region. The audiologist’s role in the operating room can be quite important.
12. I assume the audiologist is also involved in the programming of the ABI?
Most certainly. In our programming protocol for these pediatric patients, we start in the operating room (OR) with intraoperative monitoring, which we call Phase 1; that is what I have just described. Four weeks later, we go back into the OR for initial activation. The surgery can be stressful and we work quickly with our monitoring. It can take one to two hours to try numerous electrode pairs; we are looking for good electrophysiological responses and any non-auditory side effects. This is a very important because it gives us a plan on how to move forward with programming once the child is awake. Most importantly, it informs us as to which electrode pairs to stay away from when the child is awake. Next, we bring the child back for days two and three of programming. Day two of programming usually takes place in the surgeon’s office where the child's blood pressure and heart rate is monitored. The goal during day two is to activate electrode pairs that provided us with good electrophysiologic responses. Then, we employ behavioral techniques to obtain threshold and comfort levels that elicit auditory stimulation without NASE. Day three takes place at the cochlear implant center where we continue the process of looking for electrodes with good auditory stimulation without NASE. The child is then seen monthly for the first year. We often see significant psychophysical changes over the first few months.
13. Is the actual programming of the ABI much different than programming a cochlear implant?
We know the well-formed cochlea is organized in a tonotopic manner, i.e., the hair cells at the basal end of the cochlear are responsible for stimulating the higher frequency components of the auditory nerve and the apical end, the low-frequency components. Therefore, the CI audiologist doesn’t have to fuss much with modifying the channel to electrode interface. On the other hand, the tonotopic organization of the surface of the cochlear nucleus is quite variable. Often, much programming time is spent on pitch scaling and reordering of the channel to electrode interface. This is difficult in the NF2 adult population and virtually impossible in the pediatric population. With children, the assumption is that since they may be missing a cochlea or a nerve, they really haven’t formed any cochlea to nerve tonotopic relationship, as the brain needs to gradually re-organize over time.
14. Why are we doing ABI’s in children now, but not in years past?
Well, for a lot of reasons. There was interesting and encouraging data coming out of Europe with some very talented neuro-otologists (Colletti, Shannon, & Colletti, 2014) reporting low surgical complications and meaningful hearing with ABI’s. In fact, more than 50% have auditory sensations and develop closed-set speech understanding, some with open-set speech understanding and speech production. Additionally, US families were going to Europe to have these surgeries at great financial hardship and then poor follow-up would result when they arrived back in the States for device programming. Finally, there are many good ABI/CI/skull base centers in the US.
15. What kind of post-implant performance can you expect from an ABI for patients with NF2?
As with all patients with auditory prostheses, there is a range of performance, as outlined below, in a hierarchical order:
- Detection of medium to loud environmental sounds at comfortable listening levels
- Detection of conversational speech at comfortable listening levels
- Most ABI recipients should also experience:
- Improved perception of the rhythm and volume of speech resulting in improvement in speech recognition and communication ability with lip reading
- Improvement in the recognition of environmental sounds
A small number of ABI recipients will experience:
- Improved speech recognition without lip-reading
16. Do you think the pediatric ABI results will be better than the results for adult patients with NF2?
Our sample size is still fairly small, so it’s a little early to make any sweeping statements, but I think pediatric performance may be strongly dependent on etiology. That is, patients that have had a CI previously but because of multiple device failures cannot receive another implant appear to get the most benefit from an ABI. That’s because these patients have an auditory nerve and we just need to stimulate it. Individuals with an auditory nerve or those who have cochlea aplasia/hypoplasia do not appear to perform as well.
17. If an auditory nerve was not evident on imaging, would you ever try a CI for an ABI candidate in the pediatric population?
Yes. Our FDA-approved feasibility study states that if the patient has a cochlea but no evidence of an auditory nerve, we would first consider a CI. The reason for that is often a nerve cannot be seen on MRI. If a CI can be placed, it would have two advantages: lower surgical risk and the possibility of better performance for the patient. If a patient made no auditory progress over the first year, then we would consider a move to an ABI.
18. Is there any aural rehab involved in the management for patients who have an ABI?
We believe that aural rehabilitation is critical to the success of this procedure, both with adults and kids. Therapy is often performed by an experienced speech language pathologist, but audiologists can be involved in rehabilitation as well. Approximately one month after the initial stimulation, an extensive evaluation is conducted to determine the patient's present level of functioning. The therapy is initiated at that time. For the average patient, the initial therapy is similar to that of a patient with a single channel cochlear implant. Therapy may begin with work on supra-segmental training and proceed from there according to a patient’s age, auditory ability and progress.
19. Given your involvement with the pediatric ABI, do you think we need further studies to determine safety and efficacy in children?
Absolutely. Although the complications from ABI placement in the hands of an experienced neuro-surgical team is not much higher than those from CI surgery, this is a brain surgery, not an inner ear surgery. As for efficacy, we are beginning to accrue data that would suggest that the ABI can provide varying degrees of auditory benefit from sound awareness to limited open set discrimination. However, as I previously mentioned, this is extremely variable and can be based on a number of factors including etiology, cognitive ability, and others. Clearly, more research is needed.
20. Would you say that ABIs are here to stay?
I hope so—we are in the early stages of ABI with children. We know that the post-implant programming and therapy challenges that these children have are different than those of the NF2 population. Providing access to sound to these children is well worth the journey - they would otherwise be out of options. The number of children, and maybe adults, who receive little benefit from cochlear implants - depending on thier etiology - may be the largest cohort of patients to benefit from this procedure.
Colletti, V., Fiorino, F., Sacchetto, L., Miorelli, V., & Carner, M. (2001). Hearing habilitation with auditory brainstem implantation in two children with cochlear nerve aplasia.. Int J Pediatr Otorhinolaryngol, 60(2), 99-111.
Colletti, L., Shannon, R.V., & Colletti, V. (2014). The development of auditory perception in children after auditory brainstem implantation. Audiol Neurootol, 19(6), 386-94.
Jackson, K.B., Mark, G., Helms, J., Mueller, J., & Behr, R.l. An auditory brainstem implant system. Am J Audio 11(2), 128-33.
Cite this Content as:
Shapiro, W.H. (2015, November). 20Q: Auditory brainstem implants - continued advancements for both children and adults. AudiologyOnline, Article 15810. Retrieved from http://www.audiologyonline.com.