Temporal Bone Studies of the Human Peripheral Vestibular System

Abstract

Quantitative studies of the vestibular system with serially sectioned human temporal bones have been limited because of difficulty in distinguishing hair cells from supporting cells and type I from type II hair cells. In addition, there is only a limited amount of normative data available regarding vestibular hair cell counts in humans. In this study, archival temporal bone sections were examined by Nomarski (differential interference contrast) microscopy, which permitted visualization of the cuticular plate and stereociliary bundle so as to allow unambiguous identification of hair cells. The density of type I, type II, and total numbers of vestibular hair cells in each of the 5 sense organs was determined in a set of 67 normal temporal bones that ranged from birth through 100 years of age. The mean total densities at birth were 76 to 79 cells per 0.01 mm2 in the cristae, 68 cells per 0.01 mm2 in the utricle, and 61 cells per 0.01 mm2 in the saccule. The ratio of type I to type II hair cells at birth was 2.4:1 in the cristae and 1.3:1 in the maculae. There was a highly significant age-related decline in all sense organs for total, type I, and type II hair cell densities that was best fit by a linear regression model. The cristae lost type I cells with advancing age at a significantly greater rate than the maculae, whereas age-related losses for type II cells occurred at the same rate for all 5 sense organs. Hair cell densities in the cristae were significantly higher at the periphery than at the center. There were no significant sex or interaural differences for any of the counts. Mathematical models were developed to calculate the mean and 95% prediction intervals for the total, type I, and type II hair cell densities in each sense organ on the basis of age. There was overall good agreement between the hair cell densities determined in this study and those reported by others using surface preparation techniques. Our data and related models will serve as a normative database that will be useful for comparison to counts made from subjects with known vestibular disorders.

Histopathologic Changes of the Inner ear in Rhesus Monkeys After Intratympanic Gentamicin Injection and Vestibular Prosthesis Electrode Array Implantation

“…The mean type I:II HC ratios of 2.3 (SD 0.8) and 1.1 (SD 0.4) in the crista and macula, respectively, estimated in this study are in range of ratios of approximately 1.6-2.4 in the central zone of the crista (Rauch et al 2001;Lopez et al 2005) and 1.4-1.7 in the otolith end organ macula (Gopen et al 2003;Merchant et al 2000) in humans. Methods employed in this study cannot consistently distinguish between the central and peripheral zones in the cristae or striolar and nonstriolar regions in the maculae.…”

Dizziness and Imbalance in the Elderly: Age-related Decline in the Vestibular System

“…He reported a decrease in the number of vestibular hair cells after the age of 20 years old and a decrease in the number of vestibular ganglion neurons after the age of 50 years. On the other hand, Merchant et al (2000) reported a gradual loss in the number of vestibular hair cells in all endrogans, with relative sparing of the utricle, with increasing age [62]. These early reports, which estimated the number of vestibular hair cells and neurons from serial sections of the temporal bones, may have been biased as they were based on several assumptions such as the spherical shape and uniform size of the hair cells as well as the constant shrinkage and thickness of the specimen.…”

“…Gopen et al (2003) used the same method to estimate the number of hair cells in the utricle but they failed to show an agedependent decrease in the number of hair cells [64]. It remains unclear whether this result reflects the relative sparing of the utricle in age-related loss of hair cells [62], or is due to bias caused by the paucity of the number of temporal bones examined. In contrast to numerous reports regarding animal models of age-related hearing loss, animal models of agerelated vestibular dysfunction have rarely been reported.…”

Over Half the Hair Cells in the Mouse Utricle First Appear After Birth, with Significant Numbers Originating from Early Postnatal Mitotic Production in Peripheral and Striolar Growth Zones

“…In contrast, hair cell numbers in the balance organs of humans appear to reach steady levels after 14 weeks of gestation (Rosenhall 1972(Rosenhall , 1973Merchant et al 2000). Rodents are often imperfect models for human conditions, but continuing investigations in neonatal and more mature mice hold the potential to reveal just how maturational changes in mammals restrict molecular circuitry and regenerative processes that are so effective in allowing recovery of balance and hearing after damage in non-mammals.…”