Answer: Giant cell reparative granuloma

Histology: none provided

Discussion: Giant cell reparative granuloma is a benign lesion consisting of giant cells admixed with stromal cells. There is a distinctive zonal pattern of giant cells, fibrous tissue and reactive bone formation in a pattern that repeats itself over several low power fields. The lesion is not a giant cell tumor because of the zonal pattern of the histologic components. In addition, giant cell tumors involve the epiphyseal end of long bones. In the metacarpel, this would indicate the distal end rather than the proximal end as in the current case. The lesion is not a malignant fibrous histiocytoma. The cellular pleomorphism and abnormal mytotic figures characteristic of a giant cell-rich malignant fibrous histiocytoma are absent in this case. In addition, the radiographic features indicate a growing, but not rapidly growing lesion.