As the most successful neural prosthesis, cochlear implants have provided partial hearing to more than 120000 persons worldwide; half of which being pediatric users who are able to develop nearly normal language. Biomedical engineers have played a central role in the design, integration and evaluation of the cochlear implant system, but the overall success is a result of collaborative work with physiologists, psychologists, physicians, educators, and entrepreneurs. This review presents broad yet in-depth academic and industrial perspectives on the underlying research and ongoing development of cochlear implants. The introduction accounts for major events and advances in cochlear implants, including dynamic interplays among engineers, scientists, physicians, and policy makers. The review takes a system approach to address critical issues in cochlear implant research and development. First, the cochlear implant system design and specifications are laid out. Second, the design goals, principles, and methods of the subsystem components are identified from the external speech processor and radio frequency transmission link to the internal receiver, stimulator and electrode arrays. Third, system integration and functional evaluation are presented with respect to safety, reliability, and challenges facing the present and future cochlear implant designers and users. Finally, issues beyond cochlear implants are discussed to address treatment options for the entire spectrum of hearing impairment as well as to use the cochlear implant as a model to design and evaluate other similar neural prostheses such as vestibular and retinal implants.

Cochlear Implants: System Design, Integration, and Evaluation

The principles and art of plastic surgery

This paper reviews the principal English literature on hearing preservation in unilateral acoustic neuroma surgery. Seventeen case reports and 13 surgical series are included. In addition, we report ten cases of our own, two with successful hearing preservation. The purpose of this report is to study feasibility, success rate, and associated problems. Previous reports have been compared in terms of criteria that we have selected. A classification system similar to Silverstein's is used. The total number of cases under review is 621, with 221 reported successes. Cases limited to those having a unilateral acoustic neuroma, with valid supportive audiometry, were 394, with 131 successes. The approximate overall rate of success is 33%. There are five cases of hearing preservation with unilateral acoustic neuromas 3 cm or larger when supporting audiometric data are available, the largest being "4-5 centimeters." Problems included mixing of unilateral acoustic neuromas with other types of tumors and failure to include comprehensive data, particularly audiometry. We conclude 1) that hearing preservation is a reasonable goal in unilateral acoustic neuroma surgery, although the number of available candidates is relatively small and 2) that intelligent selection of patients and high quality surgical technique are the keys to success.

Hearing preservation in unilateral acoustic neuroma surgery.

This paper examines the social and cognitive processes that unfold over time as a technology develops. Our model focuses on the relationship between the beliefs researchers hold about what is and is not technically feasible, the technological artifacts they create, and the routines they use for evaluating how well their artifacts meet with their prior expectations. The historical development of cochlear implants serves as an illustration of the model. The evidence suggests that there is a reciprocal interaction between beliefs, artifacts, and routines that gives rise to two cyclical processes. One is a process of inversion at the micro level of individual cognition wherein evaluation routines designed to judge specific artifacts begin reinforcing researchers' beliefs. Once evaluation routines become the basis for constructing individual reality, technological claims are perceived as relevant only to those who employ the same routines while appearing as noise to those who employ different routines. The oth...

A Socio-Cognitive Model of Technology Evolution: The Case of Cochlear Implants

OBJECTIVE : To identify the actual benefits and persisting problems in treating vestibular schwannomas by the suboccipital approach, the results and complications in a consecutive series of 1000 tumors surgically treated by the senior author were analyzed and compared with experiences involving other treatment modalities. METHODS : Pre- and postoperative clinical statuses were determined and radiological and surgical findings were collected and evaluated in a large database for 962 patients undergoing 1000 vestibular schwannoma operations at Nordstadt's neurosurgical department from 1978 to 1993. RESULTS : By the suboccipital transmeatal approach, 979 tumors were completely removed ; in 21 cases, deliberate partial removal was performed either in severely ill patients for decompression of the brain stem or in an attempt to preserve hearing in the last hearing ear. Anatomic preservation of the facial nerve was achieved in 93% of the patients and of the cochlear nerve in 68%. Major neurological complications included 1 case of tetraparesis, 10 cases of hemiparesis, and caudal cranial nerve palsies in 5.5% of the cases. Surgical complications included hematomas in 2.2% of the cases, cerebrospinal fluid fistulas in 9.2%, hydrocephalus in 2.3%, bacterial meningitis in 1.2%, and wound revisions in 1.1%. There were 11 deaths occurring at 2 to 69 days postoperatively (1.1%). The techniques that were developed for avoidance of complications are reported. The analysis identifies preexisting severe general and/or neurological morbidity, cystic tumor formation, and major caudal cranial nerve deficits as relevant risk factors. CONCLUSION : The current treatment options of complete tumor resection with ongoing reduction of morbidity are well fulfilled by the suboccipital approach. By careful patient selection, the mortality rate should be further reduced to below 1%.

Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them.

A new approach to tumors of the skull base is described. This approach is accomplished by forward extension of the translabyrinthine opening into the cerebellopontine angle. The facial nerve is mobilized in the temporal bone from the stylomastoid foramen to its entrance into the internal auditory canal. Having removed the barrier of the facial nerve, additional bone removal can be carried forward to the internal carotid artery, which now becomes the forward limit for temporal bone resection. The access attained through this exposure allows removal of tumors arising from the petrous tip, as well as tumors arising directly from the clivus. We provide the case histories of four patients in whom this approach was successfully used in removal of skull base tumors.

The transcochlear approach to the skull base.

Electronic stimulation of hearing sensation has been achieved and tested in one patient over a period of three years. The results are encouraging and warrant more widespread testing and development of this method of rehabilitation of totally deaf patients.

Long term results of electrode implantation and electronic stimulation of the cochlea in man.

We suggest a new explanation for the lack of auditory response to electric stimulation in children with cochlear implants: the very narrow internal auditory canal, 1 to 2 mm in diameter, and the probable absence of the cochlear nerve This defect can be seen on high-resolution computed tomographic x-ray studies and may represent aplasia of the auditory-vestibular nerve We report on eight children with this anomaly, three of whom have received implants and failed to respond with a sensation of sound Identification of this problem on screening x-ray films is a contraindication to cochlear implantation for auditory stimulation

The Narrow Internal Auditory Canal in Children: A Contraindication to Cochlear Implants:

This paper presents results of a histologic study of 16 temporal bones with cochlear implants from 13 subjects. Damage caused by electrode insertion in the basal turn of the cochlea was evaluated. Dendrite and spiral ganglion cell populations were compared to clinical performance scores to determine structures necessary for stimulation and the minimum number needed for electrical stimulation. Results show that damage from insertion of long electrodes was located mainly at the most anterior part of the basal turn; that despite total degeneration of dendrites in the area near the electrode, some spiral ganglion cells remained; and that spiral ganglion cells or possibly axons are the stimulated structures and that fewer of them than previously thought are necessary to achieve a hearing sensation from electrical stimulation.

William F. House

Papers

The transcochlear approach to the skull base.

Long term results of electrode implantation and electronic stimulation of the cochlea in man.

The Narrow Internal Auditory Canal in Children: A Contraindication to Cochlear Implants:

Cochlear Implants: Histopathologic Findings Related to Performance in 16 Human Temporal Bones:

Hearing by cochlear nucleus stimulation in humans.