Undifferentiated pleomorphic sarcoma: indolent, tail-like recurrence of a high-grade tumor.

Recurrence of a soft tissue sarcoma typically manifests as a round or oval mass at imaging, and recurrent high-grade soft tissue sarcomas generally enlarge relatively rapidly. We present a case of high-grade undifferentiated pleomorphic sarcoma in the calf of a 48-year-old male that recurred as a thin, curvilinear "tail" of enhancing tissue at magnetic resonance imaging (MRI), with extremely indolent growth over a 7-year period. The unusual imaging finding of a slowly enlarging "tail" should not be dismissed as postoperative changes, even for a high-grade soft tissue sarcoma.