MRgFUS for desmoid tumors within the thigh: early clinical experiences.

BACKGROUND: Desmoid tumors are benign but locally aggressive non-malignant tumors derived from fibroblasts. Surgery, chemotherapy, and radiation therapy have been the mainstay of treatment, but recurrence is common and side effects can result in significant morbidity. In this case series, we highlight our experiences performing treatments in the thigh, including strategies for optimizing ablation size and safety.

CASE PRESENTATION: Since December 2014, 14 magnetic resonance-guided focused ultrasound (MRgFUS) treatments for desmoid tumors were performed at our institution in seven patients. Nine of these treatments were completed in three patients with large tumors within the posterior thigh. The first was a 7-year-old boy who had previously been treated with surgical resection, intra-operative radiation, along with courses of vinblastine/methotrexate and sorafenib. Pretreatment tumor volume was 770 cm3 with 75% non-enhancing volume following the initial treatment. The first treatment was complicated by a third-degree far-field skin burn. Enhanced safety measures were developed to protect the far-field skin. The patient had four subsequent treatments over 14 months, without complication, with non-perfused volume of 85% on current imaging. The second patient was a 21-year-old woman who had previously taken sulindac and celecoxib but had no other therapy. Pretreatment tumor volume was 740 cm3 . The lateral decubitus position was used to minimize the amount of energy through the sciatic nerve. The first treatment resulted in a relatively low non-perfused volume of 30%. A follow-up treatment resulted in 75-80% ablation of the target. The third patient was a 14-year-old girl with no prior treatment. Pretreatment tumor volume was approximately 440 cm3 . The sciatic nerve was encased by the anteromedial portion of the mass. A lateral decubitus position and enhanced safety measures were again used. The first treatment resulted in a relatively low non-perfused volume of 30%, likely related to low energies. The second treatment resulted in 70-80% ablation.

CONCLUSIONS: MRgFUS is an effective treatment for desmoid tumors of the thigh with a favorable side effect profile, allowing for repeated treatments if necessary. Ablation size and safety can be improved with far-field coupling devices, careful patient positioning, and optimized sonication planning.