The histochemistry of dark cells in the vestibular labyrinth

Intratympanic gentamicin: a 1-day protocol treatment for unilateral Meniere's disease

PURPOSE

The objective of this study was to assess the usefulness of low-dose intratympanic gentamicin administration in patients with Meniere's disease (MD).

MATERIALS AND METHODS

We carried out a retrospective review of the charts of 55 patients with definite MD in accordance with the AAO-HNS (American Academy of Otolaryngology-Head and Neck Surgery) Diagnostic Scale who were treated at Gruppo Otologico (Piacenza, Rome, Italy). The treatment protocol consisted of 3 intratympanic injections of gentamicin at a 12-hour interval between each administration.

RESULTS

Results were resumed in accordance with AAO-HNS criteria and showed complete control of vertigo spells in 60% (class A), good control in 16% (class B), moderate control in 4% (class C), poor control in 16% (class D), and no control in 4% (class E) of the patients. Audiological assessment showed unchanged thresholds in 61%, improvement in 22%, and worsening in 17% of the cases.

CONCLUSION

Administration of gentamicin is a good alternative to medical and surgical procedures in the treatment of intractable MD. One-day treatment allows for adequate control of vertigo attacks without compromising hearing and quality of life and with reduced costs.

Direct evidence of trigeminal innervation of the cochlear blood vessels

This paper provides the first detailed description of the trigeminal innervation of the inner ear vasculature. This system provides a newly discovered neural substrate for rapid vasodilatatory responses of the inner ear to high levels of activity and sensory input. Moreover, this discovery may provide an alternative mechanism for a set of clinical disturbances (imbalance, hearing loss, tinnitus and headache) for which a central neural basis has been speculated. Iontophoretic injections of biocytin were made via a glass microelectrode into the trigeminal ganglion in guinea-pigs. Tissue for histological sections was obtained 24 h later. Labeled fibers from the injection site were observed as bundles around the ipsilateral spiral modiolar blood vessels, as individual labeled fibers in the interscala septae, and in the ipsilateral stria vascularis. The dark cell region of the cristae ampullaris in the vestibular labyrinth was also intensively labeled. No labeled fibers were observed in the neuroepithelium of the cristae ampullaris or the semicircular canals. These results confirm and localize an earlier indirect observation of the trigeminal ganglion projection to the cochlea. This innervation may play a role in normal vascular tone and in some inner ear disturbances, e.g., sudden hearing loss may reflect an abnormal activity of trigeminal ganglion projections to the cochlear blood vessels.

Transtympanic gentamicin in the treatment of Meniére's disease

Aminoglycosides enable a pharmacological approach, before resorting to surgery, to the treatment of Menière's disease (MD) proving unamenable to routine medical treatment. The staging of MD is an essential preliminary step in the implementation of a specific and personalized treatment with transtympanic gentamicin. The ideal condition is the presence of endolymphatic hydrops with little or no damage to the cochlear and vestibular hair cells. The technical aspects of the method are discussed. In 21 patients with unilateral Menière's disease in various stages, this treatment achieved the regression of vertigo in 86% of cases; hearing was better in 19% of cases, preserved in 62% and worse in 19%; tinnitus regressed totally or partially in 62% of cases; aural fullness also regressed totally or partially in 57% of cases.

Gentamicin tympanoclysis: effects on the vestibular secretory cells

Gentamicin application to the middle ear may relieve Meniere's disease, presumably by reducing endolymph secretion by the dark cells. To explore this possibility, the ears of adult cats were treated with daily intratympanic infusions of gentamicin until ataxia occurred. The temporal bones of these cats were then examined using electron microscopy. A 3 per cent solution of gentamicin resulted in ataxia after four treatments. Acute dark cell damage to basal infoldings seen after one month persisted at six months. Treatment with a 0.3 per cent solution required 15 and 21 days to effect ataxia and resulted in a similar damage pattern. Treatment with the 0.3 per cent solution for 13 days (i.e., before ataxia developed) resulted in subtle early lesions in the basal infoldings. Such lesions might affect the rate of endolymph secretion.

10 years of experience with intratympanally applied streptomycin (gentamycin) in the therapy of Morbus Menière

During the last 10 years a total of 83 patients with severe cases of unilateral Morbus Menière were treated in our clinic. The proposed therapy was to administer streptomycin (gentamycinsulfate) intratympanically by applying two different ways of procedure. In the first group of 40 patients we attempted to destroy the vestibular organ without harming the cochlea whereby we avoided surgical intervention. In the second group of 43 patients we integrated more recent findings in the pathophysiological mechanism underlying the pathogenesis of Morbus Menière into our therapeutic considerations and attempted to exclusively destroy the secretorial epithelium with minimal dosages of aminoclycoside antibiotics. The results after treatment were clearly better for the second group of patients.

Sodium and potassium concentrations in the endolymph and perilymph of the cat

Inner ear fluid from the scala vestibuli, scala tympani, scala media, utricle, and cerebrospinal fluid were collected from 47 normal cats, and analyzed for sodium and potassium concentrations with a flame photometer. Each compartment was found to have its own different values for sodium and potassium concentration. Perilymph in the scala vestibuli possesses a lower sodium concentration than perilymph in the scala tympani; in potassium concentration the perilymph in the scala vestibuli shows a higher value than that of the scala tympani. Compared with cochlear endolymph, utricular endolymph contains a higher concentration of sodium and a lower concentration of potassium. These concentration differences, which are related to the characteristics of membrane transport in each compartment of inner ear fluid, are considered to be adequate to sustain normal biological conditions of the inner ear.