Fibromatosis or desmoid tumor covers a broad spectrum of benign fibrous tissue proliferations. It is characterized by infiltrative growth and a tendency towards recurrence; however, unlike sarcoma, it never metastasizes.
We report on a case of extraabdominal fibromatosis originating from the retroperitoneal space in a 43-year-old woman. Seven years earlier she had undergone ureterolysis and ureteroureterostomy for ureteral obstruction. Computed tomography revealed a tumor between the iliocostalis and the psoas muscle. Histopathological evaluation revealed uniform proliferation of spindle cells, with a moderate amount of collagen fibers, suggesting extraabdominal fibromatosis (desmoid tumor). The tumor was surgically resected, and since then, the patient has remained asymptomatic without any restrictions of daily living activities and without any signs of tumor recurrence during the two-year follow-up.
Complete resection is the treatment of choice. Adjuvant therapy using non steroidal anti-inflammatory agents, tamoxifen, interferon, anti-neoplastic agents, and radiotherapy, either alone or in combination finds application for unresectable or recurrent cases.