Fibrosarcoma is an uncommon, malignant spindle cell neoplasm. It appears in the metaphysis or metadiaphysis of long bones. Fibrosarcoma is found most commonly around the knee in the distal femur and proximal tibia followed by the pelvis. The tumor produces a collagen matrix but does not produce osteoid or chondroid. Fibrosarcoma can be primary or secondary due to Paget's disease, fibrous dysplasia, irradiated giant cell tumor, bone infarct or chronic osteomyelitis. Fibrosarcoma occurs both as an intramedullary and periosteal lesion. It presents in adults age 30 to 60 years old and affects men and women equally. The most common clinical presentation is that of a localized, painful mass.
     The radiologic picture of fibrosarcoma is that of an osteolytic lesion. The margins can range from well-defined to ragged and moth-eaten. Periosteal reaction is seen with cortical destruction. Extension into the soft tissue is common. MRI helps define intraosseus spread and soft tissue extension. Bone scan demonstrates increased uptake. The differential diagnosis includes leiomyosarcoma, metastatic carcinoma, melanoma, malignant fibrous histiocytoma and multiple myeloma.
     On gross examination the tumor is tan to grayish white with a rubbery consistency. Larger tumors may have hemorrhagic and necrotic foci.
     As with plain x-ray, the microscopic appearance of fibrosarcoma varies with the level of differentiation. A well differentiated, low grade tumor has homogeneous spindle shaped fibroblasts with ovoid nuclei. There is little pleom orphism and infrequent mitoses in this slow growing form. The "herring bone pattern" of fascicles of cells is prominent. Poorly differentiated or high grade tumors have pleomorphic cells, abundant mitoses and hyperchromic nuclei. They metastasize early. The cellularity of the tumor is generally in inverse proportion to the collagen production. Tumors are graded from 1 to 4 on cellularity, nuclear atypia and mitoses with high grades carrying a worse prognosis.
     Treatment of fibrosarcoma includes radical surgical excision and adjuvant radiation therapy. Prognosis is largely dependent on the tumor grade. i

i Kumar, R. et al., Fibrous Lesions of Bones, RadioGraphics, 10:237-256, March, 1990.

Marks, KE and TW Bauer, Fibrous Tumors of Bone, Orthopedic Clinics of North America, 20(3):377 393, July 1989.

Bulloughs, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.

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