When Fibrosis Mimics Cancer: A Rare Case of Idiopathic Sclerosing Mesenteritis Presenting as Locally Advanced Colonic Neoplasia

Mesenteric panniculitis (MP) is a rare benign fibroinflammatory disorder of mesenteric adipose tissue characterized by variable degrees of fat necrosis, chronic inflammation, and fibrosis. Sclerosing mesenteritis (SM) represents a predominantly fibrotic manifestation within this disease spectrum and may produce a mass‐like, infiltrative appearance that closely mimics malignant intra‐abdominal disease, making preoperative diagnosis particularly challenging. We report the case of a 56‐year‐old man who presented with progressive abdominal pain and signs of subacute intestinal obstruction. Abdominal computed tomography (CT) revealed a stenosing lesion involving the transverse colon with extension to the mesentery and anterior abdominal wall, raising strong suspicion for locally advanced colonic malignancy. The patient subsequently underwent exploratory laparotomy with segmental resection of the transverse colon and en bloc excision of the involved abdominal wall tissue. Histopathological examination unexpectedly demonstrated idiopathic SM with marked fibroinflammatory changes and no evidence of malignancy. The postoperative course was uneventful, and the patient showed progressive clinical improvement during follow‐up. This case highlights the diagnostic difficulty of SM and its ability to clinically and radiologically simulate invasive neoplastic disease. Awareness of this rare entity is essential to guide appropriate management and avoid misdiagnosis.