Ultrastructural morphology of early cellular changes in the synovium of primary synovial chondromatosis.

Synovial tissues taken from 13 cases of synovial chondromatosis (SC) were examined by light and electron microscopy. In three of the 13 cases, early cellular changes were observed by electron microscopy. Most of the foci were independently situated within an accumulation of fine, homogenous chondroid matrix in the sublining area of the synovium. Basal laminalike material was observed in these cells. Because this material was not apparent in the mature cartilage cells, the authors postulate that the basilaminar material affects cellular cytodifferentiation in SC during the initial phase of the disease. Ultrastructurally, these cells are morphologically similar to myofibroblasts. However, proliferation of paravascular cells with distinct basal laminae and activated secretory abilities was observed around some of the vessels. These paravascular cells may be the precursor cells of the prechondroblastic cells with basal laminalike material seen in SC.