This learning module describes the imaging studies for soft tissue tumors of the foot, and how to determine a potential for malignancy prior to conducting a biopsy.
Plain radiographs followed by an MRI is usually the best way to image a soft tissue tumor of the foot. Based on the clinical and radiographic information, the tumor can be classified as determinate or indeterminate. Once this determination has been made, the treatment plan follows directly.
Two orthogonal high-quality plane radiographs are recommended as the initial imaging study for soft tissue tumors. The radiographic appearance may point to a possible diagnosis. For example, intramuscular hemangiomas may contain calcified phleboliths which are visible on plain xrays, whereas synovial sarcoma may contain calcifications and invade a nearby bone, a worrisome sign associated with malignancy.
The malignant potential of some soft tissue tumors can be difficult to determine with confidence. The history and physical examination findings may be unhelpful or even misleading. All soft tissue masses over 2-cm in size should be evaluated with MRI, which provides valuable information about soft tissue masses. The MRI signal characteristics may in some cases be adequate to identify the exact nature of the lesion, or for the differential to be narrowed, but in other cases the MRI findings are nonspecific and inadequate to rule out 4 malignancy.
A new approach to assessment of the potential for malignancy has been proposed whereby soft tissue tumors are divided into two groups, "determinate" and "indeterminate", with the subsequent management plan following from this initial assessment. Tumors where a specific diagnosis is possible based on a combination of the history, the physical examination, and analysis of the MRI findings are called determinate lesions. (2) Lesions that are determinate include lipoma, hemangioma, ganglion cyst, pigmented villonodular synovitis, and aneurysm. If the clinician has sufficient confidence in his or her ability to to diagnose these lesions, they may be treated without biopsy. Other lesions cannot be identified based on the MRI findings and are called indeterminate lesions. These lesions are typically isointense with muscle on T1-weighted imaging and hyperintense on T2-weighted imaging. This group of tumors includes various soft tissue sarcomas such as synovial sarcoma, Ewing sarcoma, clear cell sarcoma, and leiomyosarcoma, as well as a number of benign tumors. Patients with indeterminate lesions should be referred to an orthopedic oncologist. A complete work-up culminated by a carefully planned and executed biopsy is necessary.
In most cases, definitive local surgical removal must await the final pathological diagnosis and should be performed as a separate procedure.
