A Dubious Pelvic Abscess in a patient with Familial Adenomatous Polyposis

Abstract A 54-year-old female presented to the Emergency Department due to 1 month lower right quadrant abdominal pain, with fever in the last 2 days. Three years before, she had been diagnosed with Familial Adenomatous Polyposis and had undergone prophylactic total proctocolectomy with ileal pouch, with no perioperative complications. Blood analysis showed an elevated C-reactive protein (7.8mg/dL). The abdominopelvic CT showed an irregular pelvic collection with air bubbles, lined by a thickened enhancing wall, lymphadenopathies and mesenteric fat densification. Endoscopic evaluation showed bulging of the ileal pouch wall. These findings were suggestive of a pelvic abscess and the patient was empirically treated with piperacillin/tazobactam, with clinical improvement. Two months later, the symptoms recurred. CT scan was repeated, showing persistence of the previously described pelvic collection, in communication with the intestinal lumen, associated with a soft tissue infiltrative tumour in the mesentery and at the site of the previous ileostomy. Endoscopic evaluation showed, in the closed end of the pouch, two fistulous openings leading to an ulcerated and friable lesion. Ultrasound-guided biopsy revealed fascicles with elongated, spindled cells of uniform appearance and pale cytoplasm, set in a collagenous stroma, without signs of cytologic atypia. Immunohistochemistry showed nuclear beta-catenin staining. These findings were suggestive of a desmoid tumour. After a multidisciplinary meeting, a derivation ileostomy was placed and systemic treatment with tamoxifen was began. This case illustrates the importance of considering the patient as a whole, including knowledge of past medical and family history, that may alert to alternative diagnosis. This case illustrates the importance of considering the patient as a whole, including knowledge of past medical and family history, that may alert to alternative diagnosis.