Double Mimicry: Chronic Diverticulitis and Post-pancreatitis Fat Necrosis Mimicking Metastatic Colonic Cancer

Inflammatory intra-abdominal conditions can occasionally mimic advanced malignancy.Post-pancreatitis fat necrosis masquerading as peritoneal carcinomatosis is a rare entity.We report a case of "double mimicry" in which severe diverticulitis and post-pancreatitis fat saponification simultaneously simulated a metastatic colonic neoplasm.A 59-year-old man with a recent episode of severe acute necrotizing pancreatitis presented with large bowel obstruction.Computed tomography (CT) and sigmoidoscopy showed an abrupt sigmoid stricture with irregular, friable mucosa, suggestive of an obstructing carcinoma.At emergency laparotomy, a hard sigmoid mass and widespread solid omental and peritoneal nodules resembling carcinomatosis were found.A diverting loop transverse colostomy was performed, and the peritoneal nodules were biopsied.Histopathology of the nodules showed fat necrosis, saponification, and calcification, with no malignancy, and endoscopic biopsies showed only inflammation.Tumor markers were normal.Considering these findings and a prior colonoscopy documenting left-sided diverticulosis, a benign etiology was favored, and the patient underwent elective laparoscopic sigmoidectomy.Final pathology confirmed severe chronic diverticulitis with reactive fibroblastic proliferation and no neoplasia.This case illustrates how two concurrent benign processes can create a convincing picture of metastatic colonic cancer.Integrating the patient's full history and obtaining histopathological confirmation are essential to avoid erroneous terminal staging and to allow definitive, curative treatment.