Periosteal chondroma. A clinicopathologic study of 23 cases.

The periosteal chondroma (juxtacortical chondroma) is an unusual tumor which usually occurs on the surface of tubular bones in the metaphyseal area. In this study, we reviewed the clinicopathologic features of 22 patients representing 23 instances of periosteal chondroma and discuss the radiologic and histologic features necessary for accurate diagnosis. The characteristic radiologic appearance is of a single cartilaginous mass in the metaphyseal periosteum causing well-defined depression or "saucerization" of the adjacent cortex. The radiologic differential diagnoses include soft-tissue tumors compressing bone, fibrous cortical defect, and periosteal chondrosarcoma or osteosarcoma. Histologic features include lobules of hyaline cartilage with frequent areas of hypercellularity, binucleate chondrocytes, and focal mild cytologic atypia. The histologic features clearly identify the tumor as chondrogenic; however, familiarity with the x-rays may be necessary to recognize the tumor as benign.