Metaplasic bone tissue in tympanosclerosis.

Two different tissues have been observed in specimens of tympanosclerotic material studied under light and electron microscopy. The first, devoid of cells and blood vessels, is a dense fibrous tissue similar to that already described in fibrous tympanosclerosis. The second resembles a bone tissue, containing osteocytes and vascular channels; it is laid down by metaplasic fibroblasts following the invasion of the first tissue by osteoclasts and blood vessels after its calcification.