Desmoplastic Fibroma

     Desmoplastic fibroma is an extremely rare tumor with less than 200 cases in the published literature. It is a slowly progressing tumor with well-differentiated cells that produce collagen. This benign tumor is characterized by aggressive local infiltration. It occurs most often in the first 3 decades and is found equally in men and women. The most common site is the
mandible, followed by the femur and pelvis. Clinical findings include pain late in the clinical course and swelling. It may present as an effusion if near a joint. Only 12% present with a pathological fracture.
     The diagnosis of desmoplastic fibroma is difficult to make radiologically. Plain xray shows an osteolytic, expansile, medullary lesion with well defined sclerotic margins. The oval tumor is often found in the metaphysis aligned with the long axis of the bone. There is usually thinned cortex and the fine intra-lesional trabeculae give a lobulated appearance that is described
as "soap-bubbly". A CT scan is only useful to further demonstrate cortical breakthrough. MRI demonstrates the separation of the intraosseus tumor from the bone. The radiological differential includes non-ossifying fibroma, giant cell tumor, UBC, ABC and fibrous dysplasia.
     Grossly, desmoplastic fibroma has a grayish to yellowish white color and a rubbery consistency. The edges are irregular, round and blunt. The tumor has occasional cystic foci with clear fluid.
     Microscopically, the tumor has interlacing bundles of dense collagen and low cellularity. The fusiform cells that are present have no atypia and the nuclei are ovoid or elongated. The differential of the tumor includes spindle cell tumors, most specifically low grade fibrosarcoma. The desmoplastic fibroma does not have the cellularity, mitotic activity or pleomorphism of a
fibrosarcoma but the distinction can be difficult and is sometimes made clinically. The edge of the tumor may resemble fibrous dysplasia, but under polarized light lamellar structures are obvious.
     Treatment of desmoplastic fibroma is marginal or wide surgical excision. Rates of recurrence are 55-72% without resection and 17% with resection.2 Recently, one study has recommended "aggressive curettage" as a surgical option. 3

References
¹Bohm, P. et al, Desmoplastic Fibroma of Bone, Cancer. 78( 5): 1011-1023, September 1, 1996.

²Bohm, P. et al.

³Nishida, J et al., Desmoplastic Fibroma, Clinical Orthopaedics and Related Research, 320: 142-148., Nov., 1995.

Bullough, Peter, Orthopaedic Pathology (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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