Andrew J. Fishman

Cochlear Reimplantation: Surgical Techniques and Functional Results

Objectives/Hypothesis The most common indication for cochlear reimplantation is device failure. Other, less frequent indications consist of “upgrades” (e.g., single to multichannel), infection, and flap breakdown. Although the percentage of failures has decreased over time, an occasional patient requires reimplantation because of device malfunction. The varying designs of internal receiver/stimulators and electrode arrays mandate an examination of the nature and effects of reimplantation for the individual designs. The purpose of the current study was to investigate the reimplantation of several implant designs and to determine whether differences in surgical technique, anatomical findings, and postoperative performance exist.

Optical cochlear implants: evaluation of surgical approach and laser parameters in cats.

Previous research has shown that neural stimulation with infrared radiation (IR) is spatially selective and illustrated the potential of IR in stimulating auditory neurons. The present work demonstrates the application of a miniaturized pulsed IR stimulator for chronic implantation in cats, quantifies its efficacy, and short-term safety in stimulating auditory neurons. IR stimulation of the neurons was achieved using an optical fiber inserted through a cochleostomy drilled in the basal turn of the cat cochlea and was characterized by measuring compound action potentials (CAPs). Neurons were stimulated with IR at various pulse durations, radiant exposures, and pulse repetition rates. Pulse durations as short as 50 mus were successful in evoking CAPs in normal as well as deafened cochleae. Continual stimulation was provided at 200 pulses per second, at 200 mW per pulse, and 100 mus pulse duration. Stable CAP amplitudes were observed for up to 10 h of continual IR stimulation. Combined with histological data, the results suggest that pulsed IR stimulation does not lead to detectable acute tissue damage and validate the stimulation parameters that can be used in future chronic implants based on pulsed IR.

Cerebrospinal Fluid Drainage in the Management of CSF Leak Following Acoustic Neuroma Surgery

A retrospective analysis was performed on 174 patients operated on from 1992 to 1995 to evaluate the safety and efficacy of continuous lumbar cerebrospinal fluid drainage (CLCFD) in the management of cerebrospinal fluid (CSF) leaks following acoustic neuroma surgery. There was a 17% incidence of CSF leak. CLCFD stopped the leak in 87% of cases. There were no cases of meningitis associated with CLCFD. One deep vein thrombosis was treated without sequelae. It is concluded that CLCFD is safe and efficacious. The authors recommend that CLCFD be implemented immediately when indicated, foregoing a trial of conservative therapy. Indications and precautions are discussed.

A review of 308 cases of revision stapedectomy

Objective/Hypothesis: Identify causes of primary and revision stapedectomy failure in 308 patients, assess whether these are different based on source of initial surgery, and evaluate hearing results in revision stapedectomy to improve outcome. Study Design: Retrospective, nonrandomized chart review of patients undergoing revision stapedectomy in a referral otology practice in a large metropolitan region. Materials and Methods: Intraoperative findings, preoperative and postoperative revision stapedectomy air and bone conduction pure‐tone averages, speech discrimination scores, postoperative air‐bone gaps, complications, and repeated revisions were noted in 308 patients. Results: Leading causes of primary stapedectomy failure included dislocated prosthesis (24.4%), inadequate prosthesis length (14%), long process resorption (14%), and fibrous adhesions (13.6%). Revision stapedectomy air‐bone gaps were less than 10 dB in 80% and greater than 30 dB in 6.8% of cases. Increased sensorineural hearing loss occurred in 0.8% of revision stapedectomy cases. Five of seven cases of vertigo associated with primary stapedectomy resolved after revision surgery. Conclusion: Revision stapedectomy by experienced surgeons is highly effective in attaining successful air‐bone gap closure in 80% and improved closure in 84.8% of operative cases. Risk of vertigo and/or sensorineural hearing loss was not any higher in this patient population when compared with reports of primary stapedectomy.

Spread of cochlear excitation during stimulation with pulsed infrared radiation: Inferior colliculus measurements

Infrared neural stimulation (INS) has received considerable attention over the last few years. It provides an alternative method to artificially stimulate neurons without electrical current or the introduction of exogenous chromophores. One of the primary benefits of INS could be the improved spatial selectivity when compared with electrical stimulation. In the present study, we have evaluated the spatial selectivity of INS in the acutely damaged cochlea of guinea pigs and compared it to stimulation with acoustic tone pips in normal-hearing animals. The radiation was delivered via a 200 µm diameter optical fiber, which was inserted through a cochleostomy into the scala tympani of the basal cochlear turn. The stimulated section along the cochlear spiral ganglion was estimated from the neural responses recorded from the central nucleus of the inferior colliculus (ICC). ICC responses were recorded in response to cochlear INS using a multichannel penetrating electrode array. Spatial tuning curves (STCs) were constructed from the responses. For INS, approximately 55% of the activation profiles showed a single maximum, ∼22% had two maxima and ∼13% had multiple maxima. The remaining 10% of the profiles occurred at the limits of the electrode array and could not be classified. The majority of ICC STCs indicated that the spread of activation evoked by optical stimuli is comparable to that produced by acoustic tone pips.

Fluoroscopically assisted cochlear implantation

Hypothesis Real-time intraoperative fluoroscopy is a useful adjunct to cochlear implantation in selected cases. The advantages include the avoidance of complications such as extracochlear array placement, intrameatal array insertion, and avoidance of significant bending or kinking. This is particularly useful when implanting a severely abnormal cochlea. Background The technique was initially developed for laboratory study of electrode prototypes in cadaver temporal bones to evaluate insertion dynamics and mechanisms of intracochlear trauma. The technique was subsequently adapted for use in live surgeries. Methods Live surgeries were performed using fluoroscopic guidance on nine patients. Results Five patients were implanted with the Nucleus 24 RCS during preclinical trials. Two patients with severe cochlear malformations were implanted with a Nucleus CI24M straight array. Two patients with severe cochlear ossification were implanted with the Nucleus CI24 double array. Appropriate insertions were achieved without electrode damage in all cases. Conclusions Intraoperative fluoroscopy is a useful adjunct to cochlear implantation, which can be performed with minimum risk to the patient and operating room staff if the outlined precautions are taken. Intraoperative fluoroscopy is indicated in cases where the intracochlear behavior of the electrode array cannot be predicted, a condition encountered when implanting new electrode designs, cases with severely malformed inner ears, or cases of severe intraluminal obstruction requiring a double-array insertion.

Total tympanic membrane reconstruction: AlloDerm versus temporalis fascia.

BACKGROUND AND OBJECTIVE: Patients who require surgery for chronic otitis media with perforation and cholesteatoma frequently provide no residual tympanic membrane that is usable in grafting procedures. A novel technique of total tympanic membrane reconstruction (TTMR) is described that maximizes perforation closure rate in these situations while minimizing mucosalization, incomplete healing, and anterior blunting. The specific aim of this report is to assess the safety and efficacy of TTMR and to compare the results obtained with AlloDerm compared with temporalis fascia as a grafting material. METHODS : The records of 50 patients operated within the years 1999 and the 2004 were reviewed. TTMR with intact canal wall was performed in all cases. Both clinical and audiometric data were analyzed. RESULTS : Overall perforation closure rate was 92%. There was no statistical significance in closure rate when grafting with AlloDerm versus temporalis fascia. A statistically significant shortened healing time was observed with AlloDerm grafting. CONCLUSIONS : TTMR is a highly effective and safe technique.

Stability of the cochlear implant array in children

Objective: To determine cochlear implant electrode stability in the young patient. Electrode migration due to future skull growth was a concern that led to prohibiting implantation in children less than 2 years of age. Recently, the high level of performance achieved by young implantees has led to a re‐evaluation of this lower age limit, requiring an assessment of the effects of skull growth over time. Study Design: Prospective radiographic analysis of electrode position of cochlear implants in young children. Methods: Twenty‐seven children implanted with the Nucleus (Cochlear Corp., Denver, CO) or Clarion (Advanced Bionics Inc., Sylmar, CA) multichannel cochlear prostheses were subjects for this study. Follow‐up radiographic studies were obtained for a period of 1 month to 5 years after implantation. The age at time of implantation ranged from 14 months to 5 years. An intraoperative modified Stenvers view plain radiograph was obtained as a baseline. After implantation, on a yearly basis transorbital Stenvers and base views were obtained for comparative purposes. Additional radiographs were obtained whenever a change in performance or electrode map caused suspicion for extrusion. Electrode position was determined using a computer graphics enhancement technique whereby image contrast filters enhanced the visibility of the electrode array and surrounding bony structures. Results: An analysis of the data revealed no migration of the electrode array over time. Conclusions: The confirmation of the stability of the electrode array alleviates the concern of the effects of skull growth on cochlear implantation in young children.

Imaging and Anatomy for Cochlear Implants

At a minimum, successful cochlear implantation requires that electrical impulses be delivered to a surviving spiral ganglion cell population, and that these impulses be transmitted to a functioning auditory cortex by an existent neural connection. Accordingly, imaging the auditory pathway of the implant candidate is necessary to screen for morphologic conditions that will preclude or complicate the implantation process. In addition to radiography, increasing resolution of computed tomography and magnetic resonance imaging technology has provided the clinician with more detailed information about the integrity of the auditory pathway.

Imaging of cochlear tissue with a grating interferometer and hard X-rays

This article addresses an important current development in medical and biological imaging: the possibility of imaging soft tissue at resolutions in the micron range using hard X‐rays. Challenging environments, including the cochlea, require the imaging of soft tissue structure surrounded by bone. We demonstrate that cochlear soft tissue structures can be imaged with hard X‐ray phase contrast. Furthermore, we show that only a thin slice of the tissue is required to introduce a large phase shift. It is likely that the phase contrast image of the soft tissue structures is sufficient to image the structures even if surrounded by bone. For the present set of experiments, structures with low‐absorption contrast have been visualized using in‐line phase contrast imaging and a grating interferometer. The experiments have been performed at the Advanced Photon Source at Argonne National Laboratories, a third generation source of synchrotron radiation. The source provides highly coherent X‐ray radiation with high‐photon flux (>1012 photons/s) at high‐photon energies (5–70 keV). Radiographic and light microscopy images of the gerbil cochlear slice samples were compared. It has been determined that a 20‐μm thick tissue slice induces a phase shift between 1/3π and 2/3π. Microsc. Res. Tech., 2009.