X-ray irradiation of the inner ear of the guinea pig. An electron microscopic study of the degenerating vestibular sensory cell

Influence of prenatal irradiation on second generation mice

Pregnant mice were irradiated with 0.5 and 2 Gy on the 13th gestational day. Offspring were raised until sexual maturity at 2 months of age. Mice from prenatally irradiated mothers and unexposed fathers, or from prenatally irradiated fathers and unexposed mothers, or from parents who had both been prenatally irradiated were mated, resulting in the birth of several mice. These second generation mice were tested as adults for hearing thresholds, with the ABR technique, subjectively to balance tests. and investigated morphologically. Hearing levels were found to be normal and the organ of Corti showed only minor changes of its inner and outer hair cells as shown by transmission and scanning electron microscopy. It is concluded that prenatal irradiation does not seem to cause mutations leading to impaired hearing and balance in second generation mice.

Vestibular apparatus disorders after external radiation therapy for head and neck cancers

External irradiation of different head and neck cancers may involve parts of the ear. The vestibular function of 25 patients in which the inner ear was comprised in the irradiated volume was investigated by electronystagmography (ENG). Doses administered to the vestibular system ranged between 2800 and 5120 cGy. Five patients suffered subjective vertigo or dizziness. Eleven patients (three out of five with vertigo) showed vestibular abnormalities to ENG (44% of the total). Altered responses to specific tests were as follow: six patients to the bithermal caloric stimulation, two to the pendular-sinusoidal test and the other three to both of them. Patients were evaluated 3 and 6 months after the ending of the radiation therapy course. At the first evaluation, abnormalities to caloric test were noted in three patients (12%) and to sinusoidal rotatory test in one patient (4%). At the second evaluation, rates of abnormal response increased to 36% and 20%, respectively. Vestibular disorders seemed to be scantly related to the total radiation dose. Data of literature are discussed in order to identify possible implications on treatment planning.

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.

Postirradiation hearing loss

Hearing loss due to irradiation of the head-and-neck region is a rarely reported complication of such a treatment. Although experimental work had been performed in laboratory animals as early as at the turn of the century, substantiated clinical data in large series are lacking. The few reports published are somewhat contradictory as to the incidence, time of onset, type and severity of the hearing loss. Although infrequently encountered, the possibility of radiation-induced hearing loss should be kept in mind. The pertinent literature is reviewed.

A scanning electron microscopic study of vestibular organ malformation following prenatal gamma irradiation

Pregnant CBA/CBA mice were exposed to 1 and 2 Gy whole-body gamma irradiation on the 13th and 16th gestational days, respectively. The litters were born on the 21st day of gestation and were tested for vestibular function at the age of 1 month. The animals were then sacrificed and their inner ears were analyzed by scanning electron microscopy. No disturbances of vestibular function were noted in the animals studied. However, the cristae ampullares showed severe malformations as regards their gross shape, with irregularities of their outer contours. Type I hair cells seemed to be more severely changed than Type II hair cells, with fusion of sensory hairs, giant hair formation and bulging of the cuticular plate. In certain sites the hair cells were totally missing. These derangements were usually located in the central areas of the cristae ampullares and in the striolar portion of the maculae utriculi. The morphological damage found showed a dose-dependent, time-related pattern.

Pathological changes during the development of the vestibular sensory and ganglion cells of the Bronx waltzer mouse. Scanning and transmission electron microscopy

Vestibular receptors and ganglia of homozygous Bronx waltzer (bv/bv) mice were investigated by scanning and transmission electron microscopy at various stages between 3 days and 90 days after birth. Scanning electron microscopy revealed that there was already a considerable lack of hair bundles in the maculae utriculi, as well as in the cristae ampullares by the 3rd day after birth. During development, the growth of the remaining hair bundles was observed but the most of them exhibited morphological abnormalities. Transmission electron microscopy revealed early degeneration of sensory cells followed by delayed maturation of the remaining sensory cells. The sensory cells which seem unaffected displayed immature features in adult animals. In type I hair cells, the calyces were incomplete, contacts between the cell and the afferent calyces were immature and synaptic bodies persisted. In some type II hair cells, there was an abnormal overabundance of afferent nerve endings, which implies that these type II cells could be immature type I cells. Immature features were also observed in the vestibular ganglia, particularly the absence of the myelin sheath around the perikarya. We discuss the relationship between these vestibular morphogenetic abnormalities and those described in the cochlear system.

Vestibular hair cell pathology following low-dose irradiation during embryonic development

Pregnant CBA/CBA mice (total gestational age 20-21 days) were whole-body irradiated on the 12th, 13th and 16th gestational days with single doses of 1 and 2 Gy using a 60Co source. Litters were taken for morphological analysis 14-21 days after birth. Irradiation on the 12th and 13th gestational days was thus performed prior to morphologic inner ear organogenesis and cytodifferentiation. In approximately 20% of the total postnatal vestibular hair cell population cytological alterations were evident: giant cytoplasmic protrusions, sensory hair fusion and disintegration of the cuticular plate. The other parts of the hair cells remained intact, including nerve endings. Morphometry was not performed. Hair cells type I are more vulnerable to ionizing irradiation during cytodifferentiation than hair cells of type II. All investigated animals showed clinically a normal balance and a normal righting reflex.

Malformations of vestibular organs following low dose gamma irradiation during embryonic development

Pregnant mice were whole-body irradiated on the 12th, 13th and 16th gestational day with single doses of 0.5, 1, 2, 3, 4, 10 and 20 Gy, using a 60Co source. No surviving litters occurred in groups exposed to more than 2 Gy. Below this dose, irradiation can cause malformation of the cristae ampullares and the maculae. Malformations were more severe and more frequent in fetuses exposed on the 12th than on the 13th gestational day, indicating that, prior to or the earlier during morphogenesis irradiation takes place, the more vulnerable is the developing tissue. Inner ears exposed to irradiation on the 16th gestational day did not reveal severe malformations.

Freeze-fracturing of vestibular sensory epithelia in a strain of the waltzing guinea pig

The waltzing guinea pig exhibits genetically induced inner ear disease which develops into deafness and vestibular disorder. The type I hair cell in vestibular end organs shows specific pathology, featuring protrusion of the hair cell apex, sensory hair fusion and an intracellular actin filament rod. With the freeze-fracturing technique, consecutive stages of degeneration of the apical part of the type I hair cell are shown. Different possible mechanisms underlying these changes are discussed. It is probable that the genetically induced prenatally developed hair cell pathology is related to a pathological development of actin filaments and their connections in the apical cytoskeleton.

The distribution of type I and type II cells in the cristae ampullaris of the guinea pig

The sensory epithelium of the crista ampullaris can be divided both structurally and as regards sensitivity to noxious agents into a central and a peripheral zone. The question is, whether this differentiation is also reflected in the distribution of the two types of sensory cells. The present electron microscopic study, based on morphometric investigations of longitudinal and transverse sections through the crista, shows that in the guinea pig, the relative distribution of the two cell types is uniform throughout the sensory epithelium. There are about 60% type I and about 40% type II cells in both the central and peripheral areas of the crista.

Degenerative changes in the human vestibular sensory epithelia

A study of the vestibular end organs from humans of different ages is presented. The inner ears were exposed by microdissection, and the vestibular sensory regions were either sectioned and studied with light or electron microscopy, or prepared and studied with the surface specimen technique. A change, which can be related to aging, is the accumulation of lipofuscin inclusions in sensory and supporting cells, especially pronounced in the type I sensory cell. Changes of the hair bundles, such as disarrangement of cilia, increased fragility of cilia and formation of giant cilia, have also been observed in aged individuals. In three cases there was a history of vestibular disturbance of vertigo. All three cases had shown caloric hypo-reactivity. In two cases, one with a history of herpes zoster oticus and another with a brain stem glioma, no morphological changes which could be attributed to the diseases, were found. The third case showed degeneration of macula utriculi and the lateral and superior cristae, possibly as a result of vascular disturbance.