Aggressive fibromatosis arising from the retroperitoneum is extremely rare. It may occur in association with previous trauma, abdominal surgery, drugs, Gardner’s syndrome, or familial adenomatous polyposis. We report a case of retroperitoneal fibromatosis presenting as a presacral mass with an infiltrating nature, relatively intense enhancement on enhanced computed tomography scanning, and low-signal intensity on T2-weighted magnetic resonance imaging in a patient with no significant medical or surgical history.
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