The role of MR imaging in soft tissue tumor evaluation: perspective of the orthopedic oncologist and musculoskeletal pathologist.

Soft tissue masses are common in both children and adults. Clinicians must evaluate patients carefully to avoid management errors. The most effective management decisions are made when a working group composed of clinicians, radiologists, and pathologists participates in the interpretation of the imaging studies. Plain-film radiographs and MR imaging scans are the two main imaging modalities used in patients with soft tissue masses. The working group assimilates the clinical and radiographic data to determine if they can identify the nature of the soft tissue mass. When the group can assign a definitive diagnosis, the lesion is designated as a determinate lesion. Determinate lesions include lipomas, ganglions, hemangiomas, neurofibromas, diabetic myonecrosis, muscle tears, myositis ossificans (heterotopic ossification), and pigmented villonodular synovitis. When the process cannot be identified, the lesion is classified as indeterminate. All soft tissue sarcomas are indeterminate lesions. Many benign lesions are also indeterminate. Common examples include schwannomas, myxomas, and giant cell tumor of tendon sheath. Based on the clinical and radiologic features, these diagnoses may be suspected, but because of the inability to distinguish them from sarcomas based on the MR imaging features, they are usually classified as indeterminate. When lesions are judged to be determinate, observation or excisional biopsy are the two major treatment choices. When lesions cannot be identified on the imaging studies, incisional or needle biopsy is performed to establish a diagnosis. Once a diagnosis is made, the proper management choice can be selected. Inappropriate excisional biopsy is the major treatment error in the management of soft tissue tumors. When a high-grade soft tissue sarcoma is resected with multiple positive margins, the risk of local failure after definitive resection is much higher than if the patient had been treated initially with only a needle or incisional biopsy. Also, if a major complication, such as an infection, a major wound-healing problem, or contamination of the major neurovascular structures, occurs at the time of incisional biopsy, amputation of the limb may be necessary. Inappropriate excisional biopsy can occur when a surgeon is not familiar with the features of sarcomas or when a radiologist mistakenly interprets the signal features as a benign lesion.