Extra-abdominal fibromatosis (desmoid tumor): a rare tumor of the lower extremity arising from the popliteal fossa

Abstract

Aggressive fibromatosis is a rare soft tissue tumor. Although it lacks metastatic potential, it can grow aggressively in a locally infiltrating pattern. The tumors frequently recur after surgical excision, which remains the treatment of choice. Optional combinations of radiotherapy and/or chemotherapy have been used postoperatively for recurrent disease and/or inoperable cases. A palpable mass was detected in the popliteal fossa of the right lower extremity in a 48-year-old man. Magnetic resonance imaging showed a contrast-enhancing noncalcified lesion initially felt to represent a vascular tumor. An invasive mass adherent to the surrounding tissue was visualized intraoperatively and extensively debulked. The patient's postoperative course was uneventful. Histologic examination of the surgical specimen was consistent with an extra-abdominal desmoid tumor. After appropriate recognition, wide local excision may be the most appropriate treatment for fibromatosis of the extremity. However, the rarity of this tumor and the difficulty inherent in distinguishing it from similar-appearing tumors are necessitating histologic confirmation of the diagnosis.

Figure 1

Axial image of MRI shows a large, expansive heterogeneous soft tissue mass with contrast, closely applied to the muscular structures, and infiltration and obliteration of adjacent structures (white asteriks).

Figure 2

Gross cross-sectional view of pathologyic resected specimen. The gross lesion is poorly circumscribed and usually measures between 5 and 15 cm. On cut section, it is hard and tan-white. The lesion is poorly circumscribed and is centered in skeletal muscle and the adjacent fascia. There often are infiltration and obliteration of adjacent structures.

Figure 3

Desmoid fibromatosis showing fascicular arrangement of bland fibroblasts, which are interrupted by thin-walled, compressed vascular channels resulting in an appearance akin to a hypocellular scar. Note entrapped muscle fibers. No mitotic activity or nuclear pleomorphism is present (H&E, original magnification, 40x).