Background: Chondroblastoma is a rare benign tumor, and reports on its cytologic features are scant. To clarify its cytologic appearance, we report a case along with immunohistochemical and electron microscopic findings.
Case: A 23-year-old male presented with a pain in his left knee, and a plain roentgenogram revealed an osteolytic lesion in the distal epiphysis of the femur. Curettage of the tumor was performed with clinical diagnosis of giant cell tumor of bone. Imprint smears showed sheetlike clusters of mononuclear tumor cells with scattered, osteoclastlike giant cells. Chondroid matrix was focally observed among the cell clusters. The histologic appearance was a conventional one, with focal chondroid matrix formation. Immunohistochemically, mononuclear tumor cells were diffusely positive for S-100 protein.
Conclusion: Cytologic features of condroblastoma are sheetlike clusters of mononuclear cells, scattered osteoclastlike giant cells and focal chondroid matrix formation. Immunohistochemical demonstration of S-100 protein in mononuclear cells helps to make a correct diagnosis.