Pigmented villonodular synovitis with chondroid metaplasia, resembling chondroblastoma of the bone: a report of three cases.

We herein describe three cases of pigmented villonodular synovitis with chondroid metaplasia. Two cases involved the temporomandibular joint, whereas the remaining one case occurred in the hip joint. Histologically, the tumors showed a villous pattern and were mainly composed of histiocyte-like cells and scattered osteoclast-like multinucleated giant cells, accompanied by chondroid areas with occasional lace-like calcification. These features resembled those of chondroblastoma of the bone, with the exception of the villous pattern. The histiocyte-like cells showed positive immunoreactivity for CD68, whereas they were negative for S-100 protein. Some of the previously reported cases of chondroblastoma in the temporal bone may have actually been cases of pigmented villonodular synovitis with chondroid metaplasia. When histologically chondroblastoma-like lesions involve the temporal bone or temporomandibular joint, the possibility of pigmented villonodular synovitis with chondroid metaplasia should also be considered, in addition to chondroblastoma of the bone. The correlation between this lesion and synovial chondromatosis remains uncertain.