Low-Grade Central Osteosarcoma Versus Fibrous Dysplasia

Abstract

Low-grade central osteosarcoma (LGCOS) is a rare subtype of osteosarcoma most commonly found in the long bones, with a predilection for the distal femur and proximal tibia. The radiographic features of low-grade central osteosarcoma are variable. Usually there is some evidence of aggressive behavior, but sometimes the findings are subtle or even consistent with a benign lesion. Histologically, LGCOS is a bone-forming tumor with a spindle cell stroma showing minimal cytologic atypia. Consequently, it is often misdiagnosed as a benign fibrous lesion, most commonly fibrous dysplasia. The treatment of choice for low-grade central osteosarcoma is resection with a wide surgical margin. Intralesional surgery is associated with a high incidence of recurrence. Therefore, a mistaken diagnosis of fibrous dysplasia can lead to undertreatment and the potential for metastases from a higher-grade recurrent tumor. At times, the radiographic features of low-grade central osteosarcoma suggest a benign lesion; however, fibrous dysplasia virtually never has a malignant radiographic appearance. The most helpful histologic features for distinguishing these tumors are permeation of pre-existing bone or marrow fat, and subtle cytologic atypia. Because clinicopathologic features overlap with fibrous dysplasia, it is important to assess carefully the clinical, radiographic, and histologic findings before making a diagnosis of low-grade central osteosarcoma.