Marsh grading system (3). Marsh grading system (3). In stage 0 (the preinfiltrative stage), there are typical small bowel villi with normal-appearing mucosa. In stage 1 (the infiltrative stage), there is a mild increase in intraepithelial lymphocytes. In stage 2 (the infiltrative hyperplastic stage), there is marked lymphocytic infiltration, mucosal edema, and proliferation of the crypts of Lieberkühn. In stage 3 (the flat destructive stage), there is partial or complete villous atrophy. In stage 4 (the atrophic hypoplastic stage), there is hypoplasia of the small bowel architecture. Progressive lymphadenopathy is seen throughout the various stages. Scholz F J et al. Radiographics 2011;31:977-992 ©2011 by Radiological Society of North America