Best cases from the AFIP: Extraabdominal desmoid-type fibromatosis

An 18-year-old woman presented with a 5-month history of an enlarging mass in the posterior aspect of her distal left calf. The mass had been diagnosed 1 month prior as desmoid-type fibromatosis by using magnetic resonance (MR) imaging and computed tomography (CT)-guided biopsy at an outside institution. At initial examination, there was a painless mass involving the Achilles tendon that measured approximately 2 × 7 cm. The initial symptoms were limited to calf tightness in the morning that resolved with stretching. Three-month observation was recommended. Eight months after diagnosis, follow-up MR images showed mild tumor progression, and 3-month observation was again recommended. Eleven months after diagnosis, follow-up MR images again showed mild progression. The mass was increasing by approximately 0.5 cm in anterior to posterior and transverse dimensions and by 1 cm in the superior to inferior dimension during the 3-month intervals. Low-dose chemotherapy with methotrexate and etoposide was instituted. However, elevated levels of liver enzymes required that the chemotherapeutic regimen be discontinued after a few months. Further treatments over the following 19 months included cryogenic ablation, radiofrequency ablation, acetic acid injections, and imatinib mesylate. These treatments were not effective; the tumor progressed to involve the popliteal fossa. The patient's range of motion was severely limited, with fixed plantar flexion of the ankle. Amputation was considered 48 months after diagnosis. Fifty-eight months after diagnosis, radiation therapy was begun with 6000 cGy at 200 cGy per fraction given over 6 weeks. Irradiation caused the tumor size to decrease by 2-3 cm.