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suppression.

If a soft tissue mass contains both areas of fat and areas that are clearly different by either MR or CT, this is usually a liposarcoma.20 The regions that appear to be muscle on CT or show high signal on T2 MRI images, should be targeted for biopsy as these are more likely to contain cells of a higher malignant grade. Lipomatous lesions may sometimes display areas of chunky ossification, indicating a nonaggressive behavior.21

Fibrous

Fibrous tumors have a density similar to muscle on plain film and CT. With MRI, low-grade fibrous lesions are musculoskeletal imaging

figure 32.1. Osteoid matrix in an osteosarcoma of the proximal fibula. The mineralization is amorphous and cloudlike.

characteristically low signal on both T1- and T2-weighted images.22 In addition to low-grade fibrous lesions, low T1 and T2 signal can also be seen with osteoid and hemosiderin. An osteoid-forming lesion can be excluded by plain film evaluation.

figure 32.2. Chondroid matrix in a chondrosarcoma. The mineralization is punctate and forms circles and arcs.

Vascular

Benign vascular lesions of soft tissue may display phleboliths on plain film or CT (Figure 32.3). With MRI, the vessels can be recognized as serpentine tubular structures that may show signal voids from flowing blood. The mass usually contains fat interspersed between the vessels, another finding suggestive of a low-grade vascular lesion.10

Although hemangiomas of the skull and vertebra have a classic imaging appearance,23 vascular tumors of bone in the extremities have no typical appearance, and even benign

figure 32.3. Soft tissue hemangioma of the calf. (A) Computed tomography (CT) image shows a mass that is lower density than muscle, suggesting the presence of fat. The punctate densities represent phleboliths, a classic finding with benign hemangiomas. (B) T1-weighted magnetic resonance (MR) scan shows signal intensity equal to subcutaneous fat around and within the mass. Note that the phle-boliths are not evident on MR.

figure 32.3. Soft tissue hemangioma of the calf. (A) Computed tomography (CT) image shows a mass that is lower density than muscle, suggesting the presence of fat. The punctate densities represent phleboliths, a classic finding with benign hemangiomas. (B) T1-weighted magnetic resonance (MR) scan shows signal intensity equal to subcutaneous fat around and within the mass. Note that the phle-boliths are not evident on MR.

hemangioma can look extremely aggressive. Angiosarcomas appear similar to sarcomas of other tissue types, but may be multifocal and cross joints, a behavior unusual for other sarcomas. It is therefore important to image the entire extremity when dealing with this tumor.24

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