Desmoid tumour of the rectus sheath following myomectomy: a mimicker of parasitic leiomyoma.

Desmoid-type fibromatosis is a rare, locally aggressive soft tissue tumour that may mimic other abdominal wall lesions. Distinguishing desmoid tumours from parasitic leiomyomas can be challenging, particularly in women with prior gynecologic surgery. A 34-year-old woman with a history of Pfannenstiel myomectomy presented with a progressively enlarging, painful left lower quadrant abdominal wall mass. Magnetic resonance imaging demonstrated a 10.5 × 8.3 × 9.4 cm lesion within the left rectus sheath concerning for recurrent leiomyoma. Given persistent symptoms and concern for parasitic leiomyoma, she underwent surgical excision with primary fascial repair. Histopathology revealed desmoid-type fibromatosis, characterized by nuclear β-catenin positivity and absence of smooth muscle marker expression. Abdominal wall desmoid tumours may closely resemble parasitic leiomyomas clinically and radiographically. Definitive diagnosis requires histopathologic and immunohistochemical evaluation. Management should be individualized and supported by multidisciplinary surveillance due to the risk of local recurrence.