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Background and Aims: In 1954 Warren and Sommers asserted that Crohn’s disease was “essentially an elephantiasis of the intestinal wall”. They described a late phase of Crohn’s disease and did not try to reconstruct the various stages of the disease. The aim of this study is to provide a step-by-step reconstruction of the anatomic changes that lead to “terminal ileitis”, i.e., to define the pathologic process.

Methods: A pathologic examination of over 100 surgical specimens of Crohn’s disease was performed. Findings were compared with those of the published literature in order to derive sequential stages in disease evolution.

Results: Terminal ileitis occurs in four different steps. The initial event is thought to be the obstruction of the ileal branch of the superior mesenteric lymphatic collector. It leads to progressive lymphatic stasis and lymphangiectasias of all the layers of lymphatics of the intestinal wall, i.e. an intestinal lymphedema (Step 1). Progressive accumulations of protein-rich lymph occur in intestinal wall, that in the mucosa result in aphthous ulcers. The increase in pressure in the intestinal lymphatic network causes rupture of superficial lymphangiectasias (Step 2). These early parietal changes allow bacterial contamination of the lymphedema which, over time, leads to chronic superficial enteritis and granulomatous lymphangitis (Step 3). Finally, fibrosis is reached (Step 4).

Conclusions: Crohn’s disease is a lymphedema of the intestinal wall contaminated by intestinal contents, ending in fibrosis. The structural changes defy therapeutic resolution.

Keywords: Crohn’s disease, lymphedema, lymphatics