MR imaging of benign soft-tissue masses of the foot and ankle.

Approximately 75% of all biopsy-proved soft-tissue masses of the foot and ankle are benign tumors or nontumoral lesions representing a variety of histologic types. In some cases, it may be difficult if not impossible to identify the lesion; however, careful analysis of the magnetic resonance (MR) imaging findings and correlation of these findings with the patient's clinical history can usually suggest a more specific diagnosis, particularly in the most common benign tumors of the foot (e.g., fibromatosis, cavernous hemangioma) and in nonneoplastic soft-tissue lesions such as Morton neuroma, ganglion cyst, and plantar fasciitis. In addition, a specific diagnosis can almost always be made in patients with pigmented villonodular synovitis (PVNS) or giant cell tumor (GCT) of the tendon sheath. The MR imaging appearance of PVNS consists of multiple synovial lesions with low or intermediate signal intensity on T1-weighted images and low signal intensity on T2-weighted and gradient-echo images. GCTs of the tendon sheath usually have areas of low signal intensity on both T1- and T2-weighted images due to the paramagnetic effect of hemosiderin. Awareness and understanding of the underlying pathologic findings in lesions of the foot and ankle aid in MR imaging interpretation.