The ultrastructure of tympanosclerotic tissue is described with particular reference to the structure of matrix vesicles and calcospherules and their role in the induction of calcification. Compared with other processes of fibrogenesis and calcification, tympanosclerosis fits well into the overall scheme of induced calcification in both normal and pathologic conditions.
Various stages of mineralization can be recognized, starting with the appearance of membrane-bound “matrix vesicles” formed in the cells of the collagenous matrix, for example, in fibroblasts; also from degenerated epithelial cells. Subsequently, crystalline inclusions are formed in the interior of the matrix vesicles. Supersaturation leads to the formation of calcospherules of laminated, serpiginous, segmented pattern or homogenous globules. Mineralization beyond the matrix vesicles leads to confluent masses or plaques. Dystrophic calcification participates in this process.
The matrix vesicles are of cellular origin and degenerating cells release them into the collagenous matrix. The mechanism is similar in all mineralizing tissues composed of collagen and protoglycons. We suggest that tympanosclerosis be-added to the so-called crystal deposition diseases.
Although it is not difficult to understand how-such a structural transformation could be common to a variety of tissues and lesions, it is less easy to imagine how this common process achieved the high degree of selectivity seen in different situations.
© 1981, The American Journal of Otology, Inc.