Histopathologic study of the perilymph-suctioned labyrinth

Methods of Hearing Preservation during Cochlear Implantation

Introduction  Recent advances in surgical techniques and electrode design have made residual hearing preservation during cochlear implantation (CI) possible, achievable, and desirable. Objectives  The objective of this study was to review the literature regarding methods used for hearing preservation during CI surgery. Data Synthesis  We performed a search in the LILACS, MEDLINE, SciELO, PubMed databases, and Cochrane Library, using the keywords CI, hearing preservation, CI electrode design, and CI soft surgery. We fully read about 15 studies that met the criteria described in "study selection". The studies showed that several factors could contribute to possible cochlear damage during or after CI surgery and must be kept in mind; mechanical damage during electrode insertion, shock waves in the perilymph fluid due to implantation, acoustic trauma due to drilling, loss of perilymph and disruption of inner ear fluid homeostasis, potential bacterial infection, and secondary intracochlear fibrous tissue formation. The desire to preserve residual hearing has led to the development of the soft-surgery protocols with its various components; avoiding entry of blood into the cochlea and the use of hyaluronate seem to be reasonably supported, whereas the use of topical steroids is questionable. The site of entry into the cochlea, electrode design, and the depth of insertion are also important contributing factors. Conclusion  Hearing preservation would be useful for CI patients to benefit from the residual low frequency, as well as for the children who could be candidate for future regenerative hair cell therapy.

Soft cochlear implantation: rationale for the surgical approach

Recent advances in cochlear implant technology have focused renewed attention on the preservation of residual hearing. The focus on preservation of residual hearing is driven by the concept of electroacoustic stimulation. This option depends on the insertion of a short cochlear implant electrode into the basal region of the cochlea while preserving native function in the apical region. The desire to preserve residual hearing has led to the development of the soft-surgery cochlear implantation technique. Here, the authors evaluate its various components. Avoiding entry of blood into the cochlea and the use of hyaluronate seem to be reasonably supported, whereas the use of topical steroids is unlikely to be beneficial. The site of entry into the cochlea, the use of contoured or straight devices, and the depth of insertion are also evaluated. The authors highlight the importance of systematic recording of outcomes and surgical events.

Acute effects of semicircular canal destruction on the cochlea, with and without preceding Pseudomonas aeruginosa exotoxin A treatment

Acute electrophysiological and morphological changes in the cochlea following destruction of the semicircular canals (SCCs) were investigated to elucidate differences in cochlear vulnerability to surgical procedure under two conditions: normal healthy condition and a pathological condition induced by Pseudomonas aeruginosa exotoxin A (PaExoA). Frequency-specific auditory brainstem response recording and examination by light microscopy (LM) and scanning electron microscopy (SEM) were performed in the acute stage, immediately following, and 2, 5, and 10 days after the intervention. All normal healthy rats showed noticeable hearing loss immediately after the operation, predominantly in lower frequency areas, followed by complete recovery within 5 days. LM revealed rupture and slight distension of Reissner's membrane. SEM revealed considerable disarray of the stereocilia, especially on the outer hair cells (OHCs) of the third row in the upper half-turns of the cochlea. By contrast, all rats under pathological conditions showed delayed and incomplete hearing recovery from postoperative hearing loss. LM revealed various kinds of cochlear reaction, such as distension of Reissner's membrane, infiltration of inflammatory cells into the cochlea, and severe inflammatory change. Damage both of inner hair cells in the basal turn and of OHCs in the upper half-turns was more noticeable, compared with that under normal conditions. These findings indicate that SCC destruction under pathological conditions induced by PaExoA is detrimental to postoperative hearing recovery, even if the preoperative hearing level had appeared electrophysiologically normal.

Perilymph fistula: concept, diagnosis and management

Perilymph fistula is caused by changes of cerebrospinal fluid pressure and/or middle ear pressure. For diagnosis, history taking is extremely important in regard to whether the occurrence of symptoms is related to physical exertion, such as straining, nose blowing, sneezing etc. A variety of symptoms are due to pathologic changes of the membranous labyrinth. Exploratory tympanotomy is needed to verify the occurrence of leakage. However, perilymph fistula cannot be excluded, even if leakage is not observed. Management consists of absolute rest and closure of the fistula. If dizziness or vertigo is intractable and long-lasting, destruction of vestibular function should be considered.

Functional changes associated with experimentally induced endolymphatic hydrops

A guinea pig model with surgically induced endolymphatic hydrops of the inner ear has been developed and studied over the past thirty years. The aim of such studies is to obtain insight into physiological processes associated with endolymphatic hydrops in man and in particular in Menière's disease where endolymphatic hydrops is systematically encountered at post-mortem examination of the temporal bones. The present review attempts to draw together the data pertaining to functional modifications of inner ear function in the animal model. For simplicity the data are categorised under five main titles: electrochemical modifications, electrophysiological modifications, pressure and hydrops, sensitivity to other insults and vestibular dysfunction. One of the most striking observations that can be made is that the data originating from different authors are very variable. There is, however, some evidence suggesting that the evolution of the auditory dysfunction could be considered as consisting of a series of different phases. This kind of information could serve as a basic framework for future research on the animal model.

Vestibular pathophysiologic changes in experimental perilymphatic fistula

An animal model of experimental perilymphatic fistula (EPLF) was developed in the guinea pig in order to study vestibular pathophysiology. In experimental animals, 4 microL of perilymph was suctioned from one cochlea via the round window membrane. Changes in vestibular function were as follows. 1) During the acute stage (5 hours postoperatively), spontaneous nystagmus directed toward the normal side was noted in 57.4% of the EPLF animals. This lasted less than 24 hours. 2) One week postoperatively, direction-fixed positional nystagmus toward the lesioned ear was present in 22.7% of the EPLF animals, especially when the lesioned ear was positioned inferiorly. 3) With the ice water caloric test, no response was present in 58.1% of the EPLF animals and an irregular response was found in 22.6% of them, 1 week postoperatively. These results tend to indicate that tests of vestibular function may differentiate between patients with Meniere's disease and those with perilymphatic fistula. Histologic findings indicate that a floating labyrinth is the cause of positional nystagmus and caloric irregularity. The absence of caloric responses was associated with collapse of the vestibular labyrinth.

Low-frequency modulation of compound action potential in experimental perilymphatic fistula and endolymphatic hydrops

We have tested the hypothesis that the cause of cochlear dysfunction associated with perilymphatic fistula (PLF) is closely related to endolymphatic hydrops (ELH). Using guinea pigs, we studied the tone-burst elicited compound action potential (CAP) and its modulation as caused by a 50 Hz biasing tone in experimental PLF. We compared these results with those of experimental ELH. Following perilymph aspiration through the perforated round window membrane, mild but significant elevations of CAP thresholds at tested frequencies were found. A reduction in the amplitude of cochlear microphonics (CM) for a 50 Hz sine wave appeared to correlate with these CAP threshold changes. However, there were no significant changes in the modulation effect of the 50 Hz biasing tone on the CAP elicited by an 8 kHz tone burst. This finding differed from that in ears with experimental ELH, in which significant reductions of both 50 Hz CM and the degree of CAP modulation were consistently observed. We concluded that it is unlikely that the underlying mechanisms of a modification to the low frequency response of the base of the cochlea following perilymph aspiration is linked to that of experimental ELH.

"Floating" labyrinth. Pathophysiology and treatment of perilymph fistula

Collapse of the membranous labyrinth of the pars superior is a morphological change observed in 50% of animals with experimentally produced perilymph fistula, although the extent and degree of the collapse may vary greatly. The moderately collapsed membranous labyrinth may drift with CSF and/or perilymph pressure changes and this may stimulate sensory cells of the utricle and/or semicircular canals if the sensory cells are intact and the collapsed wall is in contact with the otolithic membrane and/or cupula. This condition is termed "floating" labyrinth. Caloric irregularity is often observed in electronystagmograms recorded from animals with experimental perilymph fistula. This is also observed in patients with perilymph fistula. Partial destruction of the vestibular organs using argon laser was performed in a patient with perilymph fistula who was incapacitated because of persistent positional vertigo after closure of the oval window fistula. Irradiation of the argon laser beam was directed to the macula utriculi, utriculoampullary nerve and singular nerve. The hearing of the patient was maintained, and vertigo disappeared after laser labyrinthectomy.

Electronystagmographic recordings of guinea pig animal models in experimental otology

The vestibular function test in the guinea pig consists of spontaneous nystagmus recording, positional test and caloric test. If clip electrodes are used, recording of nystagmus in the guinea pig is successful. It takes less than 30 min to complete the whole test, and the animal tolerates the procedure without any complication.