Scanning electron microscopy of the organ of Corti.

With the scanning electron microscope we have examined normal cochlear sensory epithelium of the guinea pig and cat and that damaged by noise. The studies demonstrate how the regular surface architecture of the organ of Corti is altered after exposure to noise. The changes include loss of sensory hairs, formation of giant hairs, and complete degeneration of circumscribed areas of the organ of Corti. Our method greatly reduces the artifacts.

Measurement of human cochlear blood flow.

Cochlear blood flow (CBF) was measured with a laser-Doppler (L-D) flowmeter (Periflux PR2-B) in four unanesthetized human subjects with chronic tympanic membrane perforations and nine anesthetized human subjects undergoing middle ear operations. The L-D recordings were made over the promontory and/or the round window membrane during carbogen breathing and direct electrical stimulation of the cochlea in both groups and with warm water irrigation of the external ear canal in the anesthetized subjects. Carbogen led to little or no change in CBF as monitored with either measurement approach in either subject group. Electrical stimulation yielded an increase (15% to 25%) in CBF as recorded from the promontory in seven of the nine subjects tested. Warm (44 degrees C to 49 degrees C) water irrigation produced changes of 20% to 60% in CBF that were partially recoverable in the 10 minutes available for study. This study demonstrated the feasibility of direct CBF measurement in humans with the L-D method. Moreover, the data indicate that carbogen has little influence on CBF and that electrical stimulation at relatively safe levels and warm water irrigation of the ear canal produce increases in human CBF.

The innervation of the organ of Corti. A scanning electron microscopic study.

The innervation within the organ of Corti of guinea pigs, chinchillas and rabbits was studied in the scanning electron microscope. Specimens were fixed, dissected, critical point dried and coated with gold. Final dissection of the specimens was done in the dry state in the planes of the former fluid spaces. The courses of the efferent and afferent nerve fibres are described. The efferent fibres reach the outer hair cells by crossing the tunnel space, run between the outer pillars and divide several times in the space of Nuel. The afferent fibres cross the floor of the tunnel and turn basalwards in the outer spiral bundles where they run for at least 0.5-0.8 mm before connecting with the outer hair cells. Small nerve endings on every fifth to tenth outer hair cell disappear after cutting the efferent nerves, thus indicating their efferent nature.

Plaster of Paris and hair cell morphology. A scanning electron microscopic study of an alternative implant material for ear surgery.

Many techniques have been proposed for reconstruction of the posterior canal wall and/or obliteration of the mastoid bowl after radical mastoidectomy. The variety of materials that have been used, biological as well as foreign materials of different kinds, indicates that the ideal solution has yet to be found. Plaster of Paris, a biocompatible, degradable ceramic material prepared from CaSO4, may have an osteogenic property and become an alternative implant material for ear surgery. However, its possible ototoxicity has not been studied previously. Plaster was implanted in the tympanic cavity of guinea pigs. On investigation in the scanning electron microscope after 4.5 to 8 months, no toxic damage to the hair cell morphology was observed. Thus, from an ototoxic point of view, plaster of Paris would seem suitable for use as an implant material in ear surgery. Studies concerning the possible osteogenic property of plaster of Paris and its clinical application in human ear surgery are in progress.

Plaster of Paris: thermal properties and biocompatibility. A study on an alternative implant material for ear surgery.

There is no single technique for reconstruction of the canal wall following radical mastoidectomy. Autograft tissues may be unsuitable because of resorption and limited availability. An ideal foreign implant material should be bone-like in quality, non-ototoxic, readily available and malleable. Plaster of Paris, a degradable ceramic powder of CaSO4, may be regarded as a bone mineral. But a certain amount of heat develops during its solidifying process and may present a risk for injury to the facial nerve and the labyrinth. We studied the temperature rise with respect to added solution, to volume, and to surroundings, and investigated its biocompatibility when implanted in soft tissue in guinea pigs. The investigations suggested no risk of thermal injury and the biocompatibility was excellent. Hence plaster of Paris may constitute an alternative implant material for mastoid obliteration and reconstruction of the canal wall in ear surgery.

Functional histopathology of the human audio-vestibular organ. Euro-Data-Hearing.

The present paper describes the setting-up of a new project, sponsored by the Commission of the European Communities, to promote the study of functional histopathology of the human audio-vestibular organ. The project has the purpose of co-ordinating in Europe morphological research on the hearing and equilibrium organ and promoting the comparison of data from clinical, physiological and morphological studies in the field of hearing and equilibrium impairment. A manual (Iurato et al., 1982) has been prepared with the objectives of (1) stimulating clinicians to participate in the project, (2) encouraging the collection of audiological data for comparison with pathology, and (3) supplying clinicians with the necessary information about the technique of fixation and preparation of the specimens. The fixation procedures for the two major techniques of studying ear pathology: (1) microdissection and electron microscopy, and (2) embedding of the whole block for serial sectioning and light microscopy, are described in detail. Special paragraphs deal with the technique of fixation of the brain and with the technique of removal of the temporal bones and brain at autopsy. The instructions for delivery of the specimens and the publication rules are enclosed in the main body of the manual. Appendix 1 contains a list of the participating laboratories. Appendix 2 deals with autopsy legislation in the different European countries. Appendix 3 contains the sender's data sheet which supplies the instructions for collecting the clinical history of the patient and the audiological and vestibular data.

Effects of mastoid cavity obliteration on the growth of experimentally produced residual cholesteatoma.

The effects of obliteration of the mastoid cavity on the growth of residual cholesteatoma were histologically studied in an animal model. A dermal cyst was produced by grafting a piece of autologous auricular skin in the otic bulla of 11 guinea-pigs. Three weeks after grafting, part of the cyst wall facing the cavity was removed and the debris accumulated inside was inserted into the surrounding granulation using a micropick. This procedure simulates the growth mechanism of cholesteatoma residue which sometimes occurs after middle ear surgery in human subjects. In six animals, the bulla was then obliterated with plaster of Paris. The remaining five animals were used as controls. Animals were killed for histological study at 2, 4 or 8 weeks postoperatively. Microscopic examinations revealed that in the obliteration group, severe inflammatory reactions were induced in the otic bulla, although the graft epithelium survived there; dermal cyst reformed in only one of six animals. In the controls, cyst reformation was recognized in all animals. This indicated that severe inflammation induced by plaster prevented growth of the graft epithelium in the otic bulla.

Electrophysiological and morphological changes in the guinea pig cochlea following mechanical trauma to the organ of Corti.

Small discrete lesions were produced in the organ of Corti of the guinea pig cochlea using fine probes to produce direct mechanical insult. The electrophysiological state of the cochlea was assessed using N1 electrocochleography and loss of receptor cells determined by scanning electron microscopy. Principal findings were: 1) Excellent agreement between the location of hair cell losses and the frequency of maximum sensitivity change in the N1 audiogram; 2) The spatial extent of the mechanically induced lesion appears to be more important than the total number of hair cells lost, in determining the magnitude of N1 sensitivity loss; 3) Hair cell losses extending over only 72 micrometers could be detected as significant changes in N1 sensitivity. These results further emphasize the accuracy and usefulness of the N1 electrocochleogram for assessing the functional status of the cochlea; 4) Lesions involving only outer hair cell loss also produced marked elevations of N1 threshold.

Electromagnetic stimulation of the auditory system of deaf patients.

Electromagnetically induced auditory perception was investigated in 18 deaf patients who were candidates for cochlear implants. In the extracranial magnetic stimulation (EMS) procedure, patients were stimulated with time-varying magnetic field brief pulses from a coil positioned at the i) auricle, ii) the mastoid, and iii) the temporal lobe area. EMS elicited auditory sensations in 26 ears (of 14 patients/subjects). The lowest threshold of auditory sensation (TAS) was found to be at the 20% EMS level, with a range of 20-50% of the maximum level (2.0 Tesla), and approximately equal sensitivity in each coil position. Eleven of the subjects hearing EMS-induced sound perceived changes in pitch while 6 heard "clicks" or clicks and tones. Spearman Rho correlation analysis showed a mild negative correlation between the EMS/TAS and the pre-implant FFA, best tone threshold (BTT), and direct promontorial electrical stimulation (ES) thresholds at 250 Hz and 500 Hz. No correlation was found between EMS or ES and performance on the pre-implant or post-implant psychacoustic tests (MAC VIII or 3-Digit speech tests) or the measurements of the thickness of cutaneous and osseous tissue from the stimulation sites at the mastoid and ear canal to the cochlear and 8th nerve. A fair positive correlation was found between the EMS/TAS and the post-implant (6 months) ES threshold when the electrodes allocated the 500 Hz frequency range were stimulated. A mild positive correlation between the pre-cochlear-implant promontorial electrical stimulation (ES) at 250 Hz and the four frequency tone average (FFA: 0.5, 1, 2, 4 kHz) was also found.(ABSTRACT TRUNCATED AT 250 WORDS)

Inner ear damage and hearing loss after exposure to tones of high intensity.

Experimental animals (cats) were exposed to tones of 125, 1000, 2000, and 4000 Hz at sound pressure levels in the range 120 to 157.5 dB, and for durations of one hour (1000, 2000, 4000 Hz) or four hours (125 Hz). Pure tone audiograms were obtained for each animal before and after exposure. Post-exposure tests were continued until complete recovery of hearing had occurred or until a stable permanent threshold shift had been measured. Cochleas of animals were examined by phase-contrast microscopy; condition of all hair cells was recorded. Extent of inner-ear damage and range of frequencies for which hearing loss occurred increased as exposure tone was decreased in frequency. For example, exposure to 4000 Hz produced damage in a restricted region of the cochlea and hearing loss for a relatively narrow range of frequencies; exposure to 125 Hz produced wide-spread inner ear damage and hearing loss throughout the frequency range 125 to 6000 Hz.

Effects of ionomer cement on guinea pig cochleas.

The inner ear toxicity of ionomeric cement (Ionocem) when used as a reconstructive material in ear surgery was evaluated in 47 guinea pigs used in a morphological study. The cement was implanted on either the promontory, the round window membrane or the stapes. There was no significant hair cell loss compared with the control ear at three weeks, two months or three months after implantation. Using electrocochleography, the hearing thresholds before, and three weeks, two and three months after the implantation were compared in an additional seven animals. No evident hearing loss was observed in any animal during the study period. No morphological or functional evidence for an ototoxic effect of the ionomeric cement was found in this study.

Verbal information-processing capabilities and cochlear implants: implications for preoperative predictors of speech understanding.

In this study, we examined preoperative verbal cognitive capacity in 11 deafened adults who were cochlear implant candidates and reexamined level of speech understanding after 6-8 months' experience with the implant. Verbal cognitive performance in the implant group was compared in a group of normal hearing subjects and in nonimplanted group of deafened adults. The three groups performed on par with each other with an exception: The individuals in the cochlear implant group and the nonimplanted group of deafened adults performed significatly worse than those of normal hearing in tasks in which use of internal speech is a key feature (i.e., rhyme judgement and lexical decision tasks). Postoperative observations of the implanted individuals' level of speech understanding suggest that it is possible to predict the level of speech understanding by means of a properative cognitive assessment. The characteristics of three verbal cognitive abilities prove to be critical indicators of 6 - 8 months' postoperative outcome: internal speech functioning, speed of verval information processing, and working memory capacity - the first factor proved the most decisive. We discuss the results with respect to direct versus indirect predictors of outcomes from cochlear implant operations and the effect of auditory deprivation on deafened adults' capability to process auditory information.

CT diagnosis of temporal bone anomalies and cochlear implant surgery in CHARGE association.

Children with CHARGE have multiple disabilities. Impairments of vision and hearing, balance problems and facial palsy are common. Few reports have dealt with their radiological temporal bone changes and none with cochlear implant surgery. The pre-operative temporal bone computed tomography (CT) and surgical findings of one child with CHARGE and one with a CHARGE-like condition who have received cochlear implants are reported. The findings include absent semicircular canals, narrow orifice for the cochlear nerve, and abnormalities of the oval and round window, the facial canal and the ossicles. CT can be used as a diagnostic tool as these combinations of temporal bone changes are extremely rare in other materials. Cochlear implants may help these often very isolated children to communicate.

Open-set speech perception in adult cochlear implant users with ossified cochleae.

This study describes open-set speech recognition in cochlear implant subjects with ossified cochleae and compares it to a control group with open cochleae. Twenty-one postlingually deafened adults with a Med-El Combi 40/40+GB split- electrode implant were matched to patients using a Med-El cochlear implant with a standard electrode. Speech recognition was assessed over an 18-month period. Split- electrode patients improved significantly over time, but their scores were significantly lower and increased significantly slower than those of controls. Of 14 patients with a duration of deafness less than 20 years, average sentence test scores were 50%, and average monosyllabic word test scores were 31%. This study provides evidence that cochlear implantation is beneficial to patients with ossified cochleae, but early implantation is advisable.