Auditory brainstem implant

Auditory brainstem implant
Auditory brainstem implant
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Last updated January 30, 2023

An auditory brainstem implant (ABI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf, due to retrocochlear hearing impairment (due to illness or injury damaging the cochlea or auditory nerve, and so precluding the use of a cochlear implant). In Europe, ABIs have been used in children and adults, and in patients with neurofibromatosis type II.^[1]

History

The auditory brainstem implant was first developed in 1979 by William F. House, a neuro-otologist associated with the House Ear Institute, for patients with neurofibromatosis type 2 (NF2). House's original ABI consisted of two ball electrodes that were implanted near the surface of the cochlear nucleus on the brainstem. In 1997, Robert Behr at the University of Wurzburg, Germany, performed an ABI implantation using a 12-electrode array implant with an audio processor based on the MED-EL C40+ cochlear implant.^[2] The first pediatric ABI implantation was performed by Vittorio Colletti from Verona, Italy, in 1999.^[3]

In contrast to cochlear implants, ABI implantation is relatively rare. By 2010, there were only 500 patients worldwide who had undergone implantation.^[4]

Parts

An ABI system consists of an internal part (the implant) and an external part (the audio processor or sound processor). It is similar in design and function to a cochlear implant.

The external audio processor is worn on or behind the ear. It contains at least one microphone, which picks up sound signals from the environment. The audio processor converts these signals into digital signals and sends them to the coil. The coil transmits the signals through the skin to the implant below.^[5]

The internal implant sends the signals to the electrode array. The design of the electrode array is the key difference between a cochlear implant and an ABI. Whereas the electrode array for a CI is wire-shaped and is inserted into the cochlea, the electrode array of an ABI is paddle-shaped and is placed on the cochlear nucleus of the brainstem.^[3] By stimulating the brainstem, the ABI sends the sound signals to the brain, allowing the patient to perceive sound.^[5]

Indications

Neurofibromatosis Type 2

Until 2018, ABI was only indicated for patients with Neurofibromatosis Type 2 (NF2). NF2 is a genetic disorder that is characterised by the development of non-cancerous tumours along the nervous system. These vestibular schwannomas (also known as acoustic neuromas) often form on the auditory nerve, and surgical removal of these NF2 tumours can damage the auditory nerve and limiting the patient's ability to hear.^[6]

NF2 generally presents in adolescence or young adulthood, so candidacy was previously limited to patients aged 15 years or older, with NF2 and bilateral non-functioning auditory nerves.^[6]

Other Indications

In Europe and other countries, ABI is CE-marked and approved for patients 12 months and older who cannot benefit from a cochlear implant due to non-functional auditory nerves. This includes both congenital and accrued etiologies, including:

Auditory nerve aplasia
Auditory nerve hypoplasia
Head trauma
Non-NF2 tumours
Severe cochlear ossification ^[6]

The US FDA approved clinical trials of ABIs for children in 2013.^[3] A handful of medical centres, including New York University, are undergoing feasibility studies in the pediatric population.^[3]

Surgery

ABI implantation requires a craniotomy and is therefore much more complex than CI surgery. It is normally performed by both a neurosurgeon and an ENT surgeon together, who insert the electrode array through the fourth ventricle onto the surface of the cochlear nucleus.^[3]

For patients with NF2, the surgeon will spend a significant amount of time removing the acoustic neuroma tumours before inserting the implant. Depending upon the surgical approach, this may involve sacrificing the auditory nerve, thus rendering the patient deaf.^[3] Patients with NF2, who undergo both tumour removal and implantation in the same surgery, generally experience a longer post-op stay than patients without NF2.^[3]

Outcomes

Speech perception outcomes with an ABI are generally poorer than those reported in cochlear implant multichannel CI users. Most patients are able to detect the presence of environmental sounds and speech.^[3] Speech understanding gradually improves during the first three years after activation, and most patients experience better speech understanding using a combination of lip-reading and the ABI, as opposed to lip-reading alone. However, most patients are unable to understand speech using only their ABI.^[7]

There are two reasons that could explain the difference in outcomes between cochlear implants and ABIs. Firstly, non-auditory side-effects, such as vertigo, limit the overall number of electrodes that can deliver useful frequency information. Electrodes found to cause one of these side-effects are deactivated, resulting in fewer signals reaching the brain. In addition, the brainstem is unable to offer the same tonotopic range as the cochlea. With a cochlear implant, the electrodes positioned in the basal end of the cochlea elicit a higher pitch sensation than those positioned in the apical end. In contrast, the tonotopic map within the cochlear nucleus runs parallel and obliquely through the nucleus and the ABI positioned on the surface does not stimulate neural structures in such a clear, tonotopically ordered way. This makes it harder to achieve optimal results during fitting.^[7]

Patients without NF2 tend to experience better speech outcomes with an ABI than those with NF2.^[7] A study by Colletti found that a significant number of patients without NF2 were able to understand speech with an ABI, including effortless telephone use.^[8] It is believed that the tumours caused by the NF2 damage specialised cells in the cochlear nucleus important for speech perception.^[7]

There is some evidence to suggest that ABI can help to reduce the effect of tinnitus and improve quality of life.^[9] Better language outcomes are also expected with younger children implanted before the age of 2.^[10] Because of the wide range of possible outcomes, it is crucial that patients and/or their parents are counselled effectively about what they can realistically expect from an ABI. Parents are advised about additional communication modalities available, such as the use of sign language, as the ultimate goal is to facilitate language with the child.^[3]

Related Research Articles

This is a glossary of medical terms related to communication disorders which are psychological or medical conditions that could have the potential to affect the ways in which individuals can hear, listen, understand, speak and respond to others.

A cochlear implant (CI) is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. With the help of therapy, cochlear implants may allow for improved speech understanding in both quiet and noisy environments. A CI bypasses acoustic hearing by direct electrical stimulation of the auditory nerve. Through everyday listening and auditory training, cochlear implants allow both children and adults to learn to interpret those signals as speech and sound.

The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.

Auditory neuropathy (AN) is a hearing disorder in which the outer hair cells of the cochlea are present and functional, but sound information is not transmitted sufficiently by the auditory nerve to the brain. Hearing loss with AN can range from normal hearing sensitivity to profound hearing loss.

Unilateral hearing loss (UHL) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.

Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.

Neuroprosthetics is a discipline related to neuroscience and biomedical engineering concerned with developing neural prostheses. They are sometimes contrasted with a brain–computer interface, which connects the brain to a computer rather than a device meant to replace missing biological functionality.

Neurofibromatosis type II is a genetic condition that may be inherited or may arise spontaneously, and causes benign tumors of the brain, spinal cord, and peripheral nerves. The types of tumors frequently associated with NF2 include vestibular schwannomas, meningiomas, and ependymomas. The main manifestation of the condition is the development of bilateral benign brain tumors in the nerve sheath of the cranial nerve VIII, which is the "auditory-vestibular nerve" that transmits sensory information from the inner ear to the brain. Besides, other benign brain and spinal tumors occur. Symptoms depend on the presence, localisation and growth of the tumor(s), in which multiple cranial nerves can be involved. Many people with this condition also experience vision problems. Neurofibromatosis type II is caused by mutations of the "Merlin" gene, which seems to influence the form and movement of cells. The principal treatments consist of neurosurgical removal of the tumors and surgical treatment of the eye lesions. Historically the underlying disorder has not had any therapy due to the cell function caused by the genetic mutation.

<span class="mw-page-title-main">Cochlear nerve</span> Nerve carrying auditory information from the inner ear to the brain

The cochlear nerve is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information from the cochlea of the inner ear directly to the brain. The other portion of the vestibulocochlear nerve is the vestibular nerve, which carries spatial orientation information to the brain from the semicircular canals, also known as semicircular ducts.

<span class="mw-page-title-main">Cochlear nucleus</span> Two cranial nerve nuclei of the human brainstem

The cochlear nuclear (CN) complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear nucleus. At the nerve root the fibers branch to innervate the ventral cochlear nucleus and the deep layer of the dorsal cochlear nucleus. All acoustic information thus enters the brain through the cochlear nuclei, where the processing of acoustic information begins. The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.

The auditory brainstem response (ABR), also called brainstem evoked response audiometry (BERA), is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.

Binaural fusion or binaural integration is a cognitive process that involves the combination of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech as one ear may pick up more information about the speech stimuli than the other.

Cochlear is a medical device company that designs, manufactures, and supplies the Nucleus cochlear implant, the Hybrid electro-acoustic implant and the Baha bone conduction implant.

Electric acoustic stimulation (EAS) is the use of a hearing aid and a cochlear implant technology together in the same ear. EAS is intended for people with high-frequency hearing loss, who can hear low-pitched sounds but not high-pitched ones. The hearing aid acoustically amplifies low-frequency sounds, while the cochlear implant electrically stimulates the middle- and high-frequency sounds. The inner ear then processes the acoustic and electric stimuli simultaneously, to give the patient the perception of sound.

The cerebellopontine angle syndrome is a distinct neurological syndrome of deficits that can arise due to the closeness of the cerebellopontine angle to specific cranial nerves. Indications include unilateral hearing loss (85%), speech impediments, disequilibrium, tremors or other loss of motor control. The cerebellopontine angle cistern is a subarachnoid cistern formed by the cerebellopontine angle that lies between the cerebellum and the pons. It is filled with cerebrospinal fluid and is a common site for the growth of acoustic neuromas or schwannomas.

Electrocochleography is a technique of recording electrical potentials generated in the inner ear and auditory nerve in response to sound stimulation, using an electrode placed in the ear canal or tympanic membrane. The test is performed by an otologist or audiologist with specialized training, and is used for detection of elevated inner ear pressure or for the testing and monitoring of inner ear and auditory nerve function during surgery.

The frequency following response (FFR), also referred to as frequency following potential (FFP) or envelope following response (EFR), is an evoked potential generated by periodic or nearly-periodic auditory stimuli. Part of the auditory brainstem response (ABR), the FFR reflects sustained neural activity integrated over a population of neural elements: "the brainstem response...can be divided into transient and sustained portions, namely the onset response and the frequency-following response (FFR)". It is often phase-locked to the individual cycles of the stimulus waveform and/or the envelope of the periodic stimuli. It has not been well studied with respect to its clinical utility, although it can be used as part of a test battery for helping to diagnose auditory neuropathy. This may be in conjunction with, or as a replacement for, otoacoustic emissions.

MED-EL is a global medical technology company specializing in hearing implants and devices. They develop and manufacture products including cochlear implants, middle ear implants and bone conduction systems.

Temporal envelope (ENV) and temporal fine structure (TFS) are changes in the amplitude and frequency of sound perceived by humans over time. These temporal changes are responsible for several aspects of auditory perception, including loudness, pitch and timbre perception and spatial hearing.

Richard Charles Dowell is an Australian audiologist, academic and researcher. He holds the Graeme Clark Chair in Audiology and Speech Science at University of Melbourne. He is a former director of Audiological Services at Royal Victorian Eye and Ear Hospital.

References

↑ Colletti, L.; Shannon, R.; Colletti, V. (Oct 2012). "Auditory brainstem implants for neurofibromatosis type 2". Curr Opin Otolaryngol Head Neck Surg. 20 (5): 353–7. doi:10.1097/MOO.0b013e328357613d. PMID 22886036. S2CID 23791567.
↑ Jackson, Kim B.; Mark, Gerhard; Helms, Jan; Mueller, Joachim; Behr, Robert (December 2002). "An auditory brainstem implant system". American Journal of Audiology. 11 (2): 128–133. doi:10.1044/1059-0889(2002/015). ISSN 1059-0889. PMID 12691224.
1 2 3 4 5 6 7 8 9 Shapiro, William H. "20Q: Auditory Brainstem Implants - Continued Advancements for Both Adults and Children William H. Shapiro". AudiologyOnline. Retrieved 2021-11-01.
↑ Staff, Hearing Review (3 August 2010). "The Auditory Brainstem Implant: One Child's Success Story - The Hearing Review – a MEDQOR brand". www.hearingreview.com. Retrieved 2021-11-01.
1 2 Trust, Guy's and St Thomas' NHS Foundation. "Auditory brainstem implant". www.guysandstthomas.nhs.uk. Retrieved 2021-11-01.
1 2 3 "Expanded Candidacy: Auditory Brainstem Implants". MED-EL Professionals Blog. 2018-04-18. Retrieved 2021-11-01.
1 2 3 4 "Auditory brainstem implant results in adults and children". ENT & Audiology News. Retrieved 2021-11-01.
↑ Colletti, Vittorio; Shannon, Robert V. (November 2005). "Open set speech perception with auditory brainstem implant?". The Laryngoscope. 115 (11): 1974–1978. doi:10.1097/01.mlg.0000178327.42926.ec. ISSN 0023-852X. PMID 16319608. S2CID 8601242.
↑ Pinkas, Wojciech; Rajchel, Joanna J.; Dziendziel, Beata; Lorens, Artur; Skarzynski, Piotr H.; Skarzynski, Henryk (2019-12-31). "Auditory Brainstem Implantation as an Option to Improve Hearing and Reduce Tinnitus: A Retrospective Study of Four Cases". Journal of Hearing Science. 9 (4): 37–45. doi: 10.17430/1003451 . ISSN 2083-389X. S2CID 219627118.
↑ Sennaroglu, Levent; Sennaroglu, Gonca; Atay, Gamze (2013-06-01). "Auditory Brainstem Implantation in Children". Current Otorhinolaryngology Reports. 1 (2): 80–91. doi: 10.1007/s40136-013-0016-7 . ISSN 2167-583X. S2CID 71535226.