Mesothelial reaction in longstanding Crohn's ileitis simulating papillary mesothelioma.

Intestinal and extraintestinal complications of Crohn's disease are well documented. Changes in the connective tissue within the intestinal wall and surrounding tissue including mesenteric fat are characteristically seen in resected and autopsy specimens. A rare and unusually florid mesothelial reaction in the surrounding small bowel serosa of a patient with a 2-year history of Crohn's ileitis is described. The peritoneal surface of the ileal resection specimen displayed exuberant tubulo-papillary formations of the mesothelium, with superficial invasion of the underlying stroma. The case demonstrates the well-recognised difficult differential diagnosis between a benign mesothelial proliferation and malignant mesothelioma in a novel clinical setting, and the diversity of the extramural manifestations of Crohn's disease.