Perilymphatic fistula in the guinea pig

Diagnostic criteria of barotraumatic perilymph fistula based on clinical manifestations

CONCLUSIONS

Patients with sudden hearing loss and dizziness after barotrauma should be suspected of barotraumatic perilymph fistula (PLF). Early surgical repair of PLF showed better hearing outcomes. Therefore, diagnostic criteria should help surgical indications of barotraumatic PLF.

OBJECTIVES

The aim of this study was to establish diagnostic criteria for barotraumatic PLF.

METHODS

Twenty-four patients (26 ears) underwent surgery on suspicion of barotraumatic PLF. The causes of barotrauma and clinical symptoms were analyzed by surgical findings. Diagnostic criteria of PLF were proposed according to its clinical manifestations.

RESULTS

Definite PLF (17 subjects) was confirmed by any evidence of perilymph leak through oval and round windows. For the other seven subjects (probable PLF), even though there was no evidence of perilymph leak, their clinical manifestations were similar to definite PLF. High frequency hearing loss occurred as an early symptom after barotrauma. Positional dizziness occurred a few hours after auditory symptoms (67%). Positional nystagmus was observed in 10 cases. The characteristics of positional nystagmus were multi-directional, longer in duration, smaller in amplitude, no reversibility, and no response to repositioning maneuver. Regarding the surgical outcomes, hearing was significantly improved in the early repaired PFL group, and dizziness was improved in 96% of patients.

Several Mechanical Manipulations of the Wall of the Inner Ear Do Not Affect Air and Bone Conduction Auditory Thresholds

Objectives:

According to classic theories, auditory stimulation, whether air- or bone-conducted, has been thought to begin with sound-induced relative motion between the cochlear shell and the stapes footplate, producing a passive mechanical traveling wave along the basilar membrane. This study was designed to assess the effect of experimental mechanical manipulations of the cochlea on the auditory thresholds to air-conducted and bone-conducted stimulation.

Methods:

The left ear of Psammomys obesus (highest auditory sensitivity between 0.5 and 5.0 kHz) was initially ablated in all animals studied. After baseline recording of auditory nerve–brain stem evoked response (ABR) thresholds to air- and bone-conducted broadband click stimulation from the right ear, a hole was drilled in the vestibule of that ear in 3 animals. In 2 other animals, the round window of the animals was immobilized. In 3 additional animals, the round window was widely perforated. Repeat ABR thresholds were then determined.

Results:

There was no change in ABR thresholds to both air- and bone-conducted stimulation following these manipulations. The ABR wave latency also did not change.

Conclusions:

It is likely that an alternative mode of cochlear excitation is possible.

Hyperbaric compression in the guinea pig with perilymph fistula

OBJECTIVE

The study goal was to evaluate the effects of hyperbaric therapy on the auditory and vestibular function of guinea pigs compromised by perilymph fistula (PLF).

METHODS

Twenty-four pigmented guinea pigs underwent induction of bilateral eustachian tube dysfunction before the creation of a unilateral PLF. Half of the animals were randomly assigned to receive immediate hyperbaric compression treatment of 4 "dives" each. Hearing was tested electrocochleographically, and signs of vestibulopathy were recorded before and after compression.

RESULTS

After accounting for the effects of PLF, compression was not associated with significant hearing loss (P = 0.5411). Vestibulopathy was seen only in ears with PLF, and its incidence was similar for compression and noncompression groups.

CONCLUSION

Hyperbaric compression does not compromise auditory or vestibular function in guinea pig ears with experimental PLF.

SIGNIFICANCE

Our observations support the relative safety of recompression in patients with PLF.

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.

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.