What the early pathologists got wrong, and right, about the pathology of Crohn's disease: a historical perspective.

Surgeons, who documented what they had seen and felt in the abdomen of the patient, made the earliest descriptions of Crohn's disease (CD). Dalziel wrote the first pathology description in 1913. Crohn and his coworkers reinvented what Dalziel had written about and called it by a different name, 'regional enteritis'. Later others elaborated on the histologic features, at first the lymphoid follicles, later the granulomas. Some thought the latter were comprised of lymphatic endothelial cells and that endothelial plugs obstructed the lymphatics. Tonelli and others recognized that lymphedema was important and caused by obstructions to lymphatic vasculature. Some lymphatics they described contained lymphocyte plugs and others granulomas. Immunohistochemistry (IHC) has now shown that endothelial cells are not the cause of lymphatic obstruction, but rather CD68-positive macrophages, concluding that the 'lymphocyte thrombi' are passive, caught upstream of granuloma-obstructed lymphatics. Numerous authors recognized that transmural edema was the most significant change in Crohn's disease and that this was later followed by fibrosis and contracture of the diseased segment. Key descriptive papers spoke of the segmental lymphedema. Most recently, attention has been given to attachments of the intralymphatic CD68+ granulomas to a focal point where endothelial damage occurred, damage suggesting infectious penetration of the mucosa, necrosis of lymphatic endothelium and then granulomatous response, both inside and outside the lymphatics, of submucosa, muscularis, and subserosa. D2-40 IHC outlines the endothelium, and anti-CD68 shows the granulomas. IHC adds a valuable perspective when reviewing CD resections.