A 22-year-old man was admitted to our hospital with pain in the right lower quadrant. Abdominal enhanced CT showed a tumor in the pelvic cavity measuring 10 cm in size, invasion to the right external iliac vessels and the right ureter causing hydronephrosis. Volume rendering image showed many feeding vessels to the tumor from the right internal iliac artery and the ileocolic artery. The tumor was histologically diagnosed as desmoid tumor by CT-guided biopsy. Radical tumor resection and right hemicolectomy with combined resection of right ureter, right internal and external iliac vessels were performed. Diverting ileostomy, ureteroneocystostomy and bilateral femoral arteries bypass were performed, and complete tumor resection with a wide margin was able to be performed. Histological examination of the resected tumor revealed that it was comprised of uniform spindle cells arranged in flowing fascicles. Immunohistochemically, the tumor cells were positive for vimentin, ß-catenin and desmin, but not for S-100, caldesmon, CD34, ALK1, CD68 or STAT6. The tumor was histologically diagnosed as a retroperitoneal primary desmoid tumor. The ileostomy was closed 8 months after the surgery. The patient has been well more than 10 months after initial surgery, with no recurrence of disease. We report a rare case of retroperitoneal primary desmoid tumor that was treated by curative surgery with combined resection of multiple organs, while preserving postoperative anorectal and urinary functions.
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