Sunday, August 7, 2011

Desmoplastic Fibroma of Bone

Desmoplastic fibroma of bone (desmoid tumor of bone), a locally aggressive lesion related to desmoid tumors of the abdominal wall, is characterized by abundant collagen formation. This rare tumor, variably classified as benign or intermediate, accounts for less than 0.1% of all bone tumors. The tumor has a predilection for The long bones, mandible, and pelvis.

Patients are usually younger than 40 and present with nonspecific signs and symptoms. The insidious onset of signs and symptoms means that the tumor can get pretty large before presentation. Pathologic fractures, as seen in our case, are be the first presnting symptom in about 10% of cases.

Radiographs reveal a lucent lesion with a fusiform expansion of the bone. In the long bones, the lesions are metaphyseal or metadiaphyseal. Epiphyseal involvement is less common, but may occur after closure of the physis.

Internal pseudo-trabeculation, seen in 75% of cases, is due to uneven bone destruction, leaving ridges of intact bone near the periphery of the tumor.

The borders are usually non-sclerotic and sharp, but a wide zone of transition can be seen in some cases. No significant periosteal reaction is seen, but the cortex itself may be either thinned or thickened. Bone destruction and soft tissue invasion can be seen with locally aggressive forms and can mimic a malignant bone tumor.

Radiographic differential considerations include:
  • Unicameral bone cyst: Can be identical to desmoplastic fibroma on radiographs. CT and MR can be used to exclude this possibility.
  • Aneurysmal bone cyst: Eccentric expansion (blow-out) of bone is seen in aneurysmal bone cysts, compared to the more fusiform expansion of bone usually seen with desmoplastic fibroma.
  • Fibrous dysplasia: Tends to occupy a longer segment of bone than desmoplastic fibroma, has a mineralized matrix, and may have a sclerotic rim.
  • Chondromyxoid fibroma: Chondromyxoid fibroma is usually more eccentric and may have a scalloped border with thin marginal sclerosis. Pseudotrabeculations tend to be more curvilinear.
  • Giant cell tumor: Can extend into the epiphysis, but is usually round rather than oval and does not have a sclerotic margin.
  • Low-grade fibrosarcoma: Usually has a permeative pattern of bone destruction, a wider zone of transition, and no sclerotic margin.
  • Low-grade central osteosarcoma: A typical appearance is a large, intramedullary, fibro-osseous lesion with focal areas of cortical disruption, which can mimic the appearance of a desmoplastic fibroma. Typically associated with areas of mineralized tumor matrix.
  • Chondrosarcoma: Desmoplastic fibromas can contain enchondroma-like nodules that can mimic chondrosarcoma.
MRI can be helpful in further characterizing the lesion, but can be confusing in the presence of a pathologic fracture. On T1-weighted images, the lesions are isointense or hypointense to adjacent normal muscle. On T2-weighted images, the lesions have components that are iso- to hypointense to skeletal muscle. Cortical disruption and soft tissue extension are seen in about 50% of cases. Ridges of bone may result in linear areas of signal void on T2-weighted images.

Post-contrast images reveal heterogeneous enhancement, with areas of intense enhancement mixed with areas of minor to no enhancement.

MRI differential considerations of a predominantly osteolytic lesion with a large area of low T2 signal not corresponding to calcium include:
  • Lymphoma:
  • Primary leiomyosarcoma of bone:
  • Fibrous dysplasia:
  • Non-ossifying fibroma:
  • Giant cell tumor:


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