Fred F. Telischi

Auditory Brainstem Implant: I. Issues in Surgical Implantation:

Most patients with neurofibromatosis type 2 (NF2) are totally deaf after removal of their bilateral acoustic neuromas. Twenty-five patients with neurofibromatosis type 2 have been implanted with a brainstem electrode during surgery to remove an acoustic neuroma. The electrode is positioned in the lateral recess of the fourth ventricle, adjacent to the cochlear nuclei. The present electrode consists of three platinum plates mounted on a Dacron mesh backing, a design that has been demonstrated to be biocompatible and positionally stable in an animal model. Correct electrode placement depends on accurate identification of anatomic landmarks from the translabyrinthine surgical approach and also on Intrasurglcal electrophysiologic monitoring. Some tumors and their removal can result in significant distortion of the brainstem and surrounding structures. Even in the absence of Identifiable anatomic landmarks, electrode location can be adjusted during surgical placement to find the location that maximizes the auditory evoked response and minimizes activation of other monitored cranial nerves. Stimulation of the electrodes produces auditory sensations in most patients, with results similar to those of single-channel cochlear Implants. A coordinated multldlscipllnary team is essential for successful application of an auditory brainstem implant.

Vestibular effects of cochlear implantation.

Objectives/Hypothesis: Cochlear implantation (CI) carries with it the potential risk for vestibular system insult or stimulation with resultant dysfunction. As candidate profiles continue to evolve and with the recent development of bilateral CI, understanding the significance of this risk takes on an increasing importance.

Surgical management of previously untreated glomus jugulare tumors

The treatment of glomus jugulare tumors is controversial. Changes in the surgical treatment of glomus jugulare tumors at The House Ear Clinic have allowed complete resection in 85% of patients with minimal morbidity and no surgical mortalities. Our experience with 52 previously untreated patients with glomus jugulare tumors is reviewed.

Conservation of residual acoustic hearing after cochlear implantation.

Objective: This study was designed to test the hypothesis that partial hearing conservation is attainable after cochlear implantation with a long perimodiolar electrode. Surgical strategies for hearing conservation during cochlear implantation are described. Study design: Prospective, single-subject, repeated-measures design. Setting: Academic tertiary care center. Patients: Twenty-eight severely to profoundly hearing-impaired adult cochlear implant recipients who had some measurable hearing preoperatively. Intervention: Cochlear implantation using Nucleus Freedom Contour Advance electrode. Main Outcome Measures: Preimplant and postimplant pure-tone thresholds and speech recognition scores were obtained to determine the incidence and degree of conserved hearing at a mean interval of 9 (±3.9) months. Results: Thirty-two percent of subjects experienced complete conservation of hearing (0- to 10-dB loss), and 57% experienced partial conservation of hearing (>11 dB) after implantation. However, open-set speech recognition was partially conserved in only one subject. Cochlear implant performance was not better in patients with conservation of residual hearing. Conclusion: Conservation of pure-tone hearing was possible in 89% of implanted patients; however, residual speech perception was not conserved with this long perimodiolar electrode. A ceiling effect tends to inflate the prevalence of hearing conservation in implantation studies of severely to profoundly hearing-impaired patients.

Incidence and indications for revision cochlear implant surgery in adults and children

To identify the incidence of and common causes for cochlear implant revision.

Cochlear implant soft failures consensus development conference statement

COCHLEAR IMPLANT SOFT FAILURES CONSENSUS DEVELOPMENT CONFERENCE STATEMENTThis Consensus Statement was prepared by a panel of experts representing the fields of otolaryngology, audiology, speech and language pathology, communication science, and engineering. Representatives to the conference were app

Pattern of hearing loss in a rat model of cochlear implantation trauma

Hypothesis: Trauma caused by cochlear implant electrode insertion is attributable to the combination of direct physical trauma and the delayed cell death of oxidative stress-injured auditory sensory cells. Background: Histologic evaluation of cochlear implant electrode trauma has demonstrated that the extent of sensory cell losses is proportional to the degree of injury. However, the impact of delayed oxidative stress within injured cochlear tissues and the progressive loss of injured hair cells by way of apoptosis are at present unknown. Methods: Laboratory rats were evaluated for hearing acuity before and after electrode insertion, before and after round window membrane incision only. Hearing was measured before trauma or incision and over the next 7 days. Objective measurements of hearing function were distortion products of otoacoustic emissions (DPOAEs) in the frequency range of 2 to 32 kHz and tone-burst (i.e., 4-32 kHz) evoked auditory brain stem responses (ABRs). Results: For the experimental cochleae, there were progressive increases in ABR thresholds and decreases in ABR amplitudes. The amplitude of the DPOAEs in the experimental cochleae also showed progressive decreases. For the contralateral control and round window membrane surgical control ears, there were no significant changes in either DPOAE or ABR thresholds. Conclusion: These results document a progressive loss of hearing acuity postimplantation and strongly suggest that electrode insertion trauma generated oxidative stress within injured cochlear tissues.

Octreotide scintigraphy for the detection of paragangliomas

Paragangliomas are neuroendocrine tumors located primarily in the head and neck region, but they can also occur at other sites. Confirming the preoperative diagnosis and detecting synchronous tumors may be difficult in some patients. Octreotide is a somatostatin analog that, when coupled to a radioisotope, produces a scintigraphic image of tumors expressing somatostatin type 2 receptors. Paragangliomas, like many neuroendocrine tumors, have been found to have a high density of somatostatin type 2 receptors on the cell surface. This study compared the results of preoperative octreotide scintigraphy with the histopathology in 21 patients who underwent surgery for presumed head and neck paragangliomas. Octreotide scan findings were positive in 16 patients with paragangliomas and negative in 3 patients with other pathology. One false-positive and 1 false-negative result were obtained. Thus, this test had an accuracy of 90%, a sensitivity of 94%, and a specificity of 75%. Previously unidentified synchronous tumors were identified in 5 patients. On the basis of this series of patients, octreotide scintigraphy appears to be a reliable test to detect paragangliomas and may be quite helpful in preoperative planning.

Suppression and enhancement of distortion-product otoacoustic emissions by interference tones above f2. I. Basic findings in rabbits

The present study measured interference-response areas (IRAs) for distortion-product otoacoustic emissions (DPOAEs) at 2f(1)-f(2), 3f(1)-2f(2), and 2f(2)-f(1). The IRAs were obtained in either awake or anesthetized rabbits, or in anesthetized guinea pigs and mice, by sweeping the frequencies and levels of an interference tone (IT) around a set of f(1) and f(2) primary tones, at several fixed frequencies and levels, while plotting the effects of the IT on DPOAE level. An unexpected outcome was the occurrence of regions of suppression and/or enhancement of DPOAE level when the IT was at a frequency slightly less than to more than an octave above f(2). The IRA of the 2f(1)-f(2) DPOAE typically displayed a high-frequency (HF) lobe of suppression, while the 2f(2)-f(1) emission often exhibited considerable amounts of enhancement. Moreover, for the 2f(2)-f(1) DPOAE, when enhancement was absent, its IRA usually tuned to a region above f(2). Whether or not suppression/enhancement was observed depended upon primary-tone level and frequency separation, as well as on the relative levels of the two primaries. Various physiological manipulations involving anesthesia, eighth-nerve section, diuretic administration, or pure-tone overstimulation showed that these phenomena were of cochlear origin, and were not dependent upon the acoustic reflex or cochlear-efferent activity. The aftereffects of applying diuretics or over-exposures revealed that suppression/enhancement required the presence of sensitive, low-level DPOAE-generator sources. Additionally, suppression/enhancement were general effects in that, in addition to rabbits, they were also observed in mice and guinea pigs. Further, corresponding plots of DPOAE phase often revealed areas of differing phase change in the vicinity of the primary tones as compared to regions above f(2). These findings, along with the effects of tonal exposures designed to fatigue regions above f(2), and instances in which DPOAE level was dependent upon the amount of suppression/enhancement, suggested that the interactions of two DPOAE-generator sources contributed, in some manner, to these phenomena.

Measuring the cochlear blood flow and distortion-product otoacoustic emissions during reversible cochlear ischemia: a rabbit model.

Impairment to the cochlear blood flow likely induces many types of sensorineural hearing loss. Models using several small laboratory animals have been described in the literature that permit the simultaneous monitoring of the cochlear blood flow with laser-Doppler flowmetry and cochlear function using evoked responses. However, these models have not permitted a direct application of the resulting knowledge to the human condition, primarily due to differences in the translucence of the otic capsule between species. In the present study, to approximate conditions relevant to the human patient, the rabbit was utilized to develop a procedure in which laser-Doppler flowmetry could be used to measure the cochlear blood flow in an animal with an opaque otic capsule. At the same time, the cochlear function was monitored non-invasively using distortion-product otoacoustic emissions. In this manner, a laser-Doppler probe was positioned in the round window niche and the cochlear function measured using distortion-product otoacoustic emissions during a systematic series of ischemic episodes. Cochlear ischemia was produced by deliberately compressing the eighth nerve complex at the porus of the internal acoustic meatus, for periods lasting from 1-3 min, while cochlear blood flow and distortion-product otoacoustic emission measures were obtained simultaneously before, during and following the occlusion. Results demonstrated that the cochlear blood flow sharply decreased within 1 s after compression onset, whereas distortion-product otoacoustic emissions showed obstruction-induced changes after a delay of several seconds, provided that the blood flow decreased, at least 40%. Similarly, upon release of the compression, the cochlear blood flow began to recover within 1 s, whereas the recovery of the corresponding distortion-product otoacoustic emissions was slightly delayed. Although not apparent in the distortion-product otoacoustic emission recovery time course, the cochlear blood flow consistently overshot its initial baseline value during the recovery process. Thus, although cochlear ischemia produced changes in the distortion-product otoacoustic emission activity that generally followed the resulting alterations in the cochlear blood flow, the detailed relationship between the two measures was complex.