Robert A. Schindler

Cochlear patency problems in cochlear implantation

Sensory deafness may be associated with partial or total obliteration of the cochlear scalae. Before undertaking cochlear implant surgery, a preoperative assessment of cochlear patency with high‐resolution computed tomography (CT) is indicated. To determine the accuracy of pre‐implant CT, a review of the radiographic and surgical findings in 36 implanted ears was performed. An abnormal CT scan was found to be a reliable predictor of compromised cochlear patency at operation. These findings help the surgeon to select the side most favorable for implantation and to anticipate problems that may be encountered during device insertion. A normal pre‐implant CT scan, however, does not exclude the possibility of compromised cochlear patency. A 46% false negative rate was encountered, presumably because subtle degrees of osseous or fibrous obliteration of the cochlea are beyond the resolution by current generation CT scanners.

Neural Encoding of Sound Sensation Evoked by Electrical Stimulation of the Acoustic Nerve

A series of psychoacoustic experiments was conducted in subjects implanted with a permanent intracochlear bipolar electrode. These experiments were designed to reveal the nature of the sensation evoked by direct sinusoidal electrical stimulation of the acoustic nerve. A series of single unit experiments in the inferior colliculus of cats was then conducted, using intracochlear stimulus electrodes identical to those implanted in human subjects in all respects except size, and using identical stimuli. These physiological experiments were designed to reveal how sounds evoked by intracochlear electrical stimulation in humans are generated and encoded in the auditory nervous system. Among the results were the following: 1) The sensation arises from direct electrical stimulation of the acoustic nerve. It is not “electrophonic” hearing arising from electro-mechanical excitation of hair cells. 2) While sounds are heard with electrical stimulation at frequencies from below 25 to above 10,000 Hz, the useful range of discriminative hearing is limited to frequencies below 400–600 Hz. 3) There is no “place” coding of electrical stimuli of different frequency. Tonal sensations generated by electrical stimulation must be encoded by the time order of discharge of auditory neurons. 4) The periods of sinusoidal electrical stimuli are encoded in discharges of inferior colliculus neurons at frequencies up to 400–600 Hz. 5) Both psychoacoustic and physiological evidence indicates that the low tone sensations evoked by electrical stimulation are akin to the sensations of “periodicity pitch” generated in the normal cochlea. 6) Most cochlear hair cells are lost with intracochlear implantation with this electrode. Most ganglion cells survive implantation. Implications of these experiments for further development of an acoustic prosthesis are discussed.

A Quantitative Analysis of the Afferent Innervation of the Organ of Corti in Guinea Pig

A quantitative analysis of the afferent innervation of the organ of Corti was made on normal and vestibular nerve-sectioned guinea pigs. Section of the vestibular nerve at the internal auditory meatus provided an efficient means of eliminating the efferent innervation to the cochlea without significant loss of afferent fibres. Nerve counts on normal and de-efferented animals revealed that about 10-15 % of the cochlear afferent innervation supplies the outer hair cells. The remaining 85-90% of afferent fibres innervate the inner hair cells. As in cats, all tunnel spiral bundle fibres and upper tunnel crossing fibres were efferent to outer hair cells. Since unmyelinated fibres in the osseous spiral bundle were not counted, quantitative analysis of the efferent innervation to inner hair cells could not be made. However, a significant loss of myelinated fibres in the osseous spiral lamina after vestibular nerve section confirms that many myelinated efferent fibres are present in this region.

Computed tomography in suppurative ear disease: A correlation of surgical and radiographic findings

Forty‐two patients with chronic otitis media underwent preoperative CT scanning followed by surgical exploration of the middle ear and mastoid. The CT finding of abnormal soft tissue density associated with bone erosion was highly correlated with the surgical finding of cholesteatoma. By contrast, the total absence of abnormal soft tissue on CT essentially excluded cholesteatoma. However, 50% of all patients had abnormal soft tissue on CT scan not accompanied by bone erosion. In this largest group of patients it was not possible to diagnose or exclude cholesteatoma on the basis of CT findings alone. Also, CT occasionally gave the erroneous impression of lateral semicircular canal fistulization, tegmen tympani erosion, and facial nerve involvement due to volume averaging of these structures with adjacent soft tissues. CT scan has a role in the evaluation of selected patients with chronic otitis media, but must be interpreted cautiously in view of its limitations and numerous pitfalls.

Chronic Intracochlear Electrode Implantation: Cochlear Pathology and Acoustic Nerve Survival

The temporal bones of ten cats implanted with intracochlear electrodes for three to 117 weeks were stained with hematoxylin and eosin and examined with light microscopy. The electrodes were embedded in Silastic® which was molded to fill the most basal 9 mm of the scala tympani. They were inserted directly into the scala through the round window. Among our observations were the following: 1) All or nearly all hair cells were lost in the basal coil during the first several weeks after implantation. Some, but not all, supporting cells were also lost. There was extensive hair cell loss in the middle and apical turns, although some hair cells were seen there in all examined cats. 2) There was evidence of degeneration of spiral ganglion cells in the basal cochlea in several animals, but most primary auditory neurons including (with two exceptions) most of those in the region directly over the electrode, survived implantation in every cat. The radial nerve fibers of the spiral ganglion cells also survived long-term implantation. The functional viability of remaining spiral ganglion cells was confirmed in acute neurophysiological experiments conducted just before the animals were sacrificed. 3) More severe degeneration was seen in two cats in which the electrode perforated the basilar partition. In these animals, there was loss of many spiral ganglion cells, and evidence of new bone growth in the region of the perforation. 4) The appearance of the stria vascularis and spiral ligament in some implanted animals paralleled their descriptions following occlusion of the cochlear vein. 5) Connective tissue formed around the electrode surfaces, apparently displacing perilymph and sealing the electrode into the scala tympani. There was no evidence of perilymph fistula in any animal. 6) There was little evidence of progressive degeneration of the organ of Corti or spiral ganglion from three to 34 weeks after implantation. Some of the implications and limitations of these findings are discussed.

Contemporary Presentation and Management of a Spectrum of Mastoid Abscesses

Background: The incidence of complications resulting from suppurative otitis media has significantly decreased since the introduction of antibiotics. At the start of the 20th century 50% of all cases of otitis media developed a coalescent mastoiditis. By 1959, the incidence had fallen to 0.4%. Recent studies suggest a current incidence of only 0.24%. Additionally, during the time of Friedrich Bezold (1824‐1908), 20% of patients with mastoiditis developed subperiosteal abscess. Interestingly, this has incidence increased; today nearly 50% of patients diagnosed with coalescent mastoiditis have subperiosteal abscess.

Observations on an Experimental Expansile Electrode for use in Cochlear Implantation

Cochlear implants in children must be designed to allow for a childs growth and maturation. An experimental animal study was performed to document the influence of head growth on a prototype expansile electrode system. Seven kittens were implanted with a stimulated electrode which had been coiled to allow for a two-to-one expansion in length. Head growth was monitored both by direct skull measurements and by serial radiography. The animals were sacrificed when they had reached maturity and the implanted devices were studied. When implanted in subcutaneous tissue, the coils became encased in fibrous tissue, while within air-containing spaces, such as the bulla, they distended freely. This suggested that a route which maximized the amount of air-containing space traversed by an electrode should be the preferred route for a cochlear implant in children.

Mondini's dysplasia with recurrent meningitis.

This report describes the diagnosis and surgical management of two patients with similar inner ear malformations resulting in recurrent otitic meningitis. Each patient had a meningocele presenting through the oval window associated with Mondinis anomaly. Details of radiographic diagnosis and surgical management strategies will be discussed and long‐term follow‐up presented.

Cochlear implantation in children: the problem of head growth.

Successful implantation in children requires that provision be made for later head growth. The timing and magnitude of this growth was determined by measurements made from high-resolution computerized tomographic images of developing temporal bones. The temporal bone scans of 103 children of varying ages were studied. The development of the petrous and squamous portion of the temporal bone was at its greatest in the first 2 years of life. The order of magnitude of growth varied with the different axes measured.

Stapedectomy in residency training

The number of new patients with otosclerosis seen by the average otolaryngologist has declined over the past several years. As a result, a controversy has arisen regarding the ability to train residents adequately in the technique of stapedectomy. In this regard, we have analyzed 44 consecutive stapedectomies performed by senior residents, under direct faculty supervision, at the University of California, San Francisco. All procedures were total stapedectomies, performed under local anesthesia, utilizing either wire‐vein or wire perichondrium technique. Four of the ears required footplate or promontory drilling. Closure to within 10 dB of the preoperative bone conduction, averaged over the speech frequencies of 500, 1000, and 2000 Hz, was achieved in 75% of ears, and closure to within 20 dB in 93% of ears. In no patient was hearing made worse. While there were no permanent complications, self‐limited problems occurred in 9% of the procedures.