A Rare Case of Desmoid Fibromatosis in a Pediatric Patient: Surgical Management and Outcomes.

Desmoid fibromatosis (DF) is a rare, locally aggressive tumor arising from the abdominal fascia or musculoaponeurosis, commonly affecting individuals between 15 and 60 years of age. We present a case of a 13-year-old boy with a 9-month history of progressive swelling in the left posterior thigh. Magnetic resonance imaging (MRI) revealed a soft tissue tumor encasing the sciatic nerve. A biopsy confirmed the diagnosis of DF, showing spindle cells arranged in fascicles. The patient underwent wide local excision of the tumor with preservation of the sciatic nerve. Postoperative recovery was smooth, and 1-year follow-up MRI showed no recurrence. Surgical excision remains the primary treatment, especially in symptomatic patients, although recurrence is common even with negative margins. This case underscores the importance of regular follow-up for DF and a multidisciplinary approach to optimize management and surveillance.