SEM observations on development of human otoconia during the first trimester of gestation

The early development of human otoconial membranes was studied by scanning electron microscopy and X-ray microanalysis; 87 specimens, ranging from 7 to 12 weeks gestational age were examined. A few otoconia, which contained calcium, were present in the utricle by the end of the seventh week. By 8 weeks, both the saccule and utricle contained otoconia and differentiation of the macular neuroepithelia was well underway. At all stages, the utricular otoconia appeared more mature and were more varied in size and shape than saccular otoconia. In 12-week specimens, the maculae were covered by otoconial membranes with clearly defined crystalline and gelatinous layers. Near the end of the first trimester, newly-formed otoconia were present on the inferior utricular wall. X-ray analysis showed that a marked increase in otoconial calcium content occurs during the period from 7 to 12 weeks gestational age.