Auditory Brainstem Implants (eBook)

1 The History and Development of Auditory Brainstem Implants

Kevin A. Peng and Derald E. Brackmann

Abstract

The auditory brainstem implant (ABI), which was conceived by William F. House at the House Ear Institute in Los Angeles, California in the 1970s, is a device that provides auditory sensation by directly stimulating the cochlear nucleus of the brainstem. By bypassing the cochlea and the cochlear nerve, it has become an invaluable resource for hearing rehabilitation in patients with neurofibromatosis type 2. Additional clinical advances have expanded the use of ABIs to pediatric patients, and additional research may establish other clinical applications.

Keywords: auditory brainstem implant, neurofibromatosis type 2

1.1 Early Work in Stimulation of the Brainstem

The first report of stimulation of the human brainstem was published in 1964. In this study, Simmons et al stimulated the inferior colliculus, but this yielded no sound perception or awareness.1 Several years elapsed before any significant advances were made. At the House Ear Institute (HEI) in Los Angeles, California, William F. House had begun surgical placement of cochlear implants in the late 1960s. He realized that auditory rehabilitation in patients with no auditory nerves, such as patients with neurofibromatosis type 2, remained unaddressed.

House began to design a device to stimulate the cochlear nucleus of the brainstem directly. He enlisted the assistance of Jean Moore, a neuroanatomist at HEI. Moore mapped out the target area for brainstem implantation. Based on his prior experience with the development of the cochlear implant, House designed an initial device with a two-ball-electrode configuration. This communicated percutaneously with an external receiver.

On May 24, 1979, House and William E. Hitselberger operated on a 51-year-old female with a vestibular schwannoma in her only-hearing ear. Following tumor resection, they placed the first auditory brainstem implant (ABI) with the electrode residing next to the cochlear nucleus. This was percutaneously coupled with a modified body-worn Bosch hearing aid. This provided the patient with sound awareness, but by 1980, the patient developed a sensation of “twitching” in the ipsilateral leg. The electrode was deemed to have migrated. The patient continued to use the ABI and external processor until her death in her late 80s.

In conjunction with Douglas McCreery of the Huntington Medical Research Institute (HMRI), House designed a new electrode with a Dacron mesh backing, to which an increasing number of electrodes was later added (▶ Fig. 1.1). This mesh was designed to provide increased stability of the electrode after implantation. In 1981, the original subject underwent a second surgery. The prior electrode was removed, and the new Dacron mesh electrode was placed on the surface of the brainstem. This ABI allowed once again for auditory sensation, and was paired several years later with a House-Sigma single-channel cochlear implant processor. The patient continues to use the ABI and external processor to this day.2 A seminal paper by Edgerton et al later summarized the preliminary efforts and physiology of direct stimulation of the cochlear nucleus.3

1.2 Auditory Brainstem Response and Advances in Device Manufacturing

In 1982, Michael D. Waring, an audiologist working with HEI, recorded the first electrically evoked auditory brainstem response from the first ABI recipient previously discussed. This provided additional encouragement, and HEI began to construct and evaluate electrode designs for future ABI devices. J. Phil Mobley and Franco Portillo, engineers with HEI, supervised the installation of fabrication facilities at HEI. In 1984, the first implantation of an ABI device fabricated at HEI was performed.

In 1985, three patients underwent ABI placement. Broken wires and electrode migration were both encountered, but nonetheless the implants showed promise. Technical details were described in a subsequent publication by McElveen et al, which confirmed the feasibility of using the ABI for auditory stimulation.4 In 1986, HEI received investigational device exemption status from the Food and Drug Administration (FDA) to pursue the ABI program.

Another advance came in 1987, when Portillo suggested the use of braided wires rather than single-stranded wires. Braided wires were more flexible and less prone to breakage. Derald E. Brackmann, a neurotologist at HEI, worked with Portillo to improve the reliability and biocompatibility of the percutaneous plug. The same year, Eisenberg et al published the first audiological perspective on the ABI, confirming that ABI recipients experienced tone perception and significant auditory discrimination exceeding what is expected due to chance.5

1.3 Development of Modern Processors and Multi-electrode Arrays

House-Sigma cochlear implant processors were adapted for ABIs in 1984. Thereafter, a collaboration between 3M (Maplewood, Minnesota, USA) and HEI led to the development of the Alpha processor, again an improvement over the House-Sigma cochlear implant processors. In 1991, HEI and Cochlear (Sydney, Australia) began to collaborate on developing an eight-electrode array. This was completed in 1992.

Steve R. Otto, a clinical audiologist at HEI, began to provide and refine maps for ABI patients around this time, including performance testing. Meanwhile, the ABI program was clinically spearheaded by Derald E. Brackmann. Research on auditory performance at HEI was overseen by Robert V. Shannon. Clinical trials for the ABI were initiated in the United States in 1993, and the device later gained FDA approval in 2000. Array development had continued during this time, and by the time FDA approval was obtained, the new array contained 21 electrodes paired with Cochlear’s nucleus speech processor.6

In parallel, MED-EL (Innsbruck, Austria) began to develop a multi-electrode array. Advanced Bionics (Valencia, California, USA) also began work on a proprietary ABI. In 1997, Robert Behr performed the first ABI in Europe at the University of Wurzburg, Germany. This device was a 12-electrode array developed by MED-EL with a speech processor based on the Combi 40 + cochlear implant processor.

1.4 The Penetrating Auditory Brainstem Implant

In the early 2000s, the HEI began work on development of a penetrating electrode for the ABI. This was conceived on the basis of the tonotopic organization of the cochlear nucleus, where low acoustic frequencies were located superficially and high frequencies were located more deeply. The pilot penetrating ABI (PABI) device included eight penetrating electrodes paired with a 12-electrode surface electrode array, and the first PABI was implanted in July 2003. A second-generation device, with two additional penetrating electrodes and a higher allowable charge limit, was first implanted in 2005.

By 2007, nine PABI patients had been implanted. The benefits of the PABI included a lower threshold for stimulation, increased frequency range, and high selectivity. Fewer than 25% of penetrating electrodes resulted in auditory stimulation, while more than 60% of surface electrodes were effective.

PABI patients were evaluated with three different maps: surface electrodes only, penetrating electrodes only, and a combination of the two. Patients with the PABI did not demonstrate improved speech recognition when compared to a cohort of patients implanted with surface electrode devices.7 As the device was more complex to manufacture and implant than the surface-array-only ABI, further development of the PABI was deferred.

1.5 New Horizons for ABI

In 1999, Vittorio Colletti, of the University of Verona, implanted the first ABI in a pediatric patient with deficient cochlear nerves.8 He proceeded to implant the ABI in several additional pediatric patients, and some achieved open-set recognition. Pediatric ABI is now being performed at select centers in the United States and elsewhere. Recently, Roberts et al once again described the phenomenon of tinnitus suppression in a subset of ABI patients, a topic that will require further research.9

Over the past four decades, the ABI has been established as an invaluable tool for hearing rehabilitation in NF2 patients. Additional research is planned to determine candidacy, identify predictive factors for performance, and expand clinical applications.

Acknowledgments

The authors wish to acknowledge Steve R. Otto, MA, and William M. Luxford, MD, for their invaluable assistance with elucidating the chronology of the development of the ABI.

References

[1] Simmons FB, Mongeon CJ, Lewis WR, Huntington DA. Electrical stimulation of acoustical nerve and inferior colliculus. Arch Otolaryngol. 1964; 79: 559–568

[2] Hitselberger WE, House WF, Edgerton BJ, Whitaker S. Cochlear nucleus implants. Otolaryngol Head Neck Surg. 1984; 92(1):52–54

[3] Edgerton BJ, House WF, Hitselberger W. Hearing by cochlear nucleus stimulation in humans. Ann Otol Rhinol Laryngol Suppl. 1982; 91(2 Pt 3):117–124

[4] McElveen JT, Jr, Hitselberger WE, House WF, Mobley JP, Terr LI. Electrical stimulation of cochlear nucleus in man. Am J Otol. 1985...