Morphogenesis and malformation of otoconia: A review

Very little information is available concerning the pathology of otoconia, due partly to the difficulty of studying microscopic organic crystals, partly to the inadequacy of the conventional process for decalcification used in histopathologic study of temporal bone for studying details of otoconia, and partly to the difficult of assessing dysfunction of the gravity receptors. Numerous mutant mice have been reported to have hyperactivity (waltzing or circling behavior), and many of these mutants are also known to have dysgenesis or agenesis of the vestibular sensory organ. While hyperactive behavior may be related to a central neurologic problem, it is also possible that vestibular disorder contributes to this behavior. Of particular interest in these animal models is that certain mineral supplementation of the diet (manganese, zinc) during the critical period of gestation (during otoconial formation) can prevent the otoconial deficiency. In addition, the availability of the transmission and scanning electron microscopes, with x-ray diffraction capability and the x-ray analyzer, have added a new dimension to the understanding of the ultrastructure, morphology, morphogenesis, and pathology of the otoconia. Because of this improved ultrastructural information, we have begun to interpret the light microscopic findings on the otoconia with a certain confidence, as light microscopic findings can be correlated well with electron microscopic observations of the same specimen. Furthermore, behavioral and physiologic tests have been developed. These results can be correlated with the degree of otoconial deficiency, providing a great opportunity to study function in the gravity receptors. Some information which may be vital in understanding the aplasia and dysplasia of otoconia, mainly in animals, will be reviewed in the hope that this will stimulate research in human otoconial pathology, which remains a virtually untouched area in otoneurology.