Meniére's disease. Electron microscopy of the vestibular ganglion and end organs after ultrasound

Ultrastructural changes in the hydropic cochlea of the guinea-pig

Transmission electron microscopy of the cochlear organ of Corti in experimental endolymphatic hydrops revealed two principal features. Starting 1 month after induction of hydrops, osmiophilic inclusions thought to represent lipofuscin accumulation were frequently observed in the subcuticular cytoplasm of the outer hair cells along the length of the cochlea. Starting 3 months after induction of hydrops the efferent terminals on the outer hair cells appeared to be vacuolated. These data suggest that oxidative insult is likely to contribute to the pathology associated with endolymphatic hydrops and thus that free radical scavengers might be useful in the treatment of Menière's disease patients. In addition the early modification of the efferent innervation of the hydropic cochlea might underlie the known hypersensitivity to various insults, including noise stimulation, glycerol administration and hypoxia.

Ultrastructural aspects of the human peripheral vestibular system

The sensory epithelia from the membranous labyrinths of 4 patients were examined by transmission electron microscopy. The distribution ratio of type 1 to type 2 cells was recorded, compared for each sensory area and correlated with age. An ultrastructural assessment confirmed generalized patterns consistent with autolytic and preparation artefact, viz. calyceal dilatation, cytoplasmic protrusions and some sensory hair loss. More specific features, i.e. lipofuscin accumulation, membrane-bound inclusions and neural degeneration were consistent with pre-mortem pathological change. In 2 patients, total nerve fibre counts of 15,766 and 19,741 were obtained. Total fibre counts correlated with the sensory cell density of the innervated areas. Differential counts of the superior and inferior vestibular nerves suggested that there was a reduced number of fibres in the superior division of both patients, in comparison with established normative data. Morphometric analysis of the constituent fibre diameters revealed a skewed distribution with a modal value of 6 microns for both patients.

Ultrastructure of the vestibular sensory organs in delayed endolymphatic hydrops

Vestibular sensory organs were examined ultrastructurally in two cases of delayed endolymphatic hydrops. The patients, two women, 27 and 16 years of age, suffered profound sensory hearing loss in childhood and experienced severe, recurrent vertigo. Specimens were obtained by a translabyrinthial vestibular nerve transection. We studied the utricular macula and the lateral and posterior cristae in one case, and the utricular macula, the anterior and posterior cristae, and the vestibular ganglion in the other. The otoconia and the otoconial membrane, the sensory epithelia, and the vestibular ganglion appeared fairly normal. Although the entire vestibular end organs were not studied in these cases, it was surprising that the ultrastructural findings did not conclusively identify vestibular end organ pathology as the cause of the vertigo attacks.

Ultrastructural findings on human Scarpa's ganglion

The morphology of human Scarpa's ganglion from two surgically removed specimens as well as from four autopsy preparations from patients without clinical evidence of vestibular dysfunction was investigated. Ganglion cell circumference varied between 45 and 160 microns. More than half of the nerve cells ranged between 90 and 110 microns. The arrangement of ganglion cells, nerve fibres and endoneural connective tissue appeared better preserved in autopsy preparation than in biopsy specimens. Electron microscopy revealed that in half of the investigated specimens, neuroglial tissue was present as far distal as the vestibular ganglion. Almost all ganglion cells were surrounded by one or several layers of satellite cells, and did not reveal myelination. From the present study we cannot predict if neuronal function in human beings differs from that in other animals, although morphological differences do exist.

Investigations into the cause of canal paresis in Menière's disease

Since the literature has a paucity of documented lesions of the vestibular hair cells and neurons in Menière's disease, the cause of canal paresis remains unexplained. A clinicopathological correlation was sought and demonstrated between ampullary distortion of lateral canal and reduced caloric response. The findings in this investigation make a strong case for ampullary distortion disrupting the tenuous but vital cupulary attachment resulting in canal paresis. This concept is attractive because it explains an important clinical event in Menière's disease on the basis of the only consistent histopathological finding, namely, membrane distension.

[Electron microscopic investigation of connective tissue in vestibular ganglion and nerve in morbus Menière]

Vestibular ganglia of 17 patients with Menière's disease, obtained by transtemporal or translabyrinthine neurectomy, were studied by electron microscopy. Three ganglia removed because of other disease and four ganglia of normal ears taken post mortem served as controls. The neuronal fibrous tissue of Menière cases showed without exception pathologic changes of various extent. The amount of collagen was increased, whereby different fiber diameters were observed as well as changes in the periodicity of cross banding. Signs of continuing collagen formation were found: active fibroblasts and an increased number of isolated Schwann cells without axons, showing deerhorn-like ramifications which enveloped collagen bundles. The blood vessels were frequently surrounded by multiple basal membranes and broad bands of homogenous matrix. The pericytes were either necrotic or nonexistent. The endothelial cell cytoplasma was usually not in an active state. Sometimes it seemed to be autolytic. The pinocytotic activity was strikingly diminished. These qualitative changes of the interstitial tissue might point to a local pathologic event in the region of the vestibular nerve and ganglion.

Macula utriculi in four cases with Meniere's disease

Four patients suffering from Meniere's disease were labyrinthectomized. Maculae utriculi were removed and studied by electron microscopy. The neuro-epithelia from all four patients appeared fairly normal, considering the age of the patients. However, two types of degenerative change, which could be related to the inner ear disorder, could be distinguished. One was vacuolation of the sensory cell cytoplasm, followed by pycnosis of the nucleus and cell death. The other was cystic degeneration. This started with localized separations between the sensory cell and the nerve chalice. These separations developed into a single cystic cavity. A few large intra-epithelial cysts were found, probably representing the final stage of the cystic degenerative process.

The morphology of the vestibular nerve in a patient with normal vestibular function and in patients with Ménière's disease

The morphology of the vestibular nerve was studied in three fresh nerve specimens obtained by surgery from two patients with Ménière's disease and one patient with tinnitus after an attack of sudden deafness. The number of nerve fibres appeared light microscopically normal. The vestibular ganglion cells of the Ménière-specimens showed, as a characteristic finding advanced vesiculation of the cytoplasm. This change was confirmed by electron microscopy and the vacuoles appeared to consist of widened endoplasmic reticulum cisternae. Numerous primary lysosomes and lipofuscin granules were observed in all vestibular ganglion cells but their number appeared increased in the specimens from Ménière-patients. Some of the vestibular ganglion cells of these patients showed a filamentous appearance and the number of glycogen granules seemed reduced in all of them. All vestibular ganglion cells observed were unmyelinated. The degenerative changes observed might explain the typical elevation of the threshold for vestibular stimulation in Ménière's disease.