Extra-Abdominal Fibromatosis (Desmoid Tumor): A Rare Tumor of the Lower Extremity Arising from the Popliteal Fossa
A 48-year-old man presented with a tender swelling in his right lower extremity of 3 months’ duration. Physical examination revealed a visually obvious 8 × 9 cm pulsatile mass on the lateral margin of the popliteal fossa. The distal extremity was stiff and tender to palpation. There was no previous history of trauma or surgical intervention. Lower extremity Doppler ultrasonography showed an 8 × 9 × 1 0-cm solid heterogeneous mass in the lateral popliteal fossa. Magnetic resonance imagining (MRI) demonstrated a large mass that closely approximated the muscular structures and surrounding connective tissue. The lesion was felt to represent a vascular mass.
Intraoperatively, the patient was placed in the supine position under epidural anesthesia. The lesion was adherent to surrounding tissues including muscle and nerve. It originated from the muscular fascia of the deep muscle within the popliteal fossa. The lesion itself was large, gray-white, fibrotic, and irregular. Its appearance was not typical of a vascular lesion. No infiltration of the surrounding large vessels was identified, but the tumor invested nerves in the popliteal fossa. As this mass was thought to be suspicious for malignancy, enbloc dissection of the tumor was then carried out, including dissection of its attachments to the deep popliteal region, accomplished with the assistance of orthopedic and neurological surgeons. Total excision was attempted, but was unsuccessful as a tumor segment 0 . 5 × 0 . 5cm in diameter which heavily infiltrated the tibial nerve could not be excised. Macroscopic surgical margins were free from all aspects of the tumor mass. Postoperatively, pathologic examination demonstrated widespread proliferation of spindle-shaped cells and collagen fibers. There were rare mitoses, but no signs of atypia were seen (arrow). Microscopic tumor margins were negative, and there was no evidence of malignant change.
The patient’s early postoperative course was uneventful. The patient refused any subsequent radiotherapy or chemotherapy, and he was discharged on the 9th postoperative day. Eighteen months later, he is free from disease without evidence of local recurrence or distant metastasis.
Fig.1 : Axial image of MRI shows a large, expansive heterogeneous soft tissue mass with contrast, closely applied to the muscular structures, and infiltration
Fig.2 : Gross cross-sectional view of pathologyic resected specimen. The gross lesion is poorly circumscribed and usually measures between 5 and 15 cm.
Fig.3 : Desmoid fibromatosis showing fascicular arrangement of bland fibroblasts, which are interrupted by thin-walled