Histological findings of microscopic colitis Classic Lymphocytic Colitis Classic Collagenous Colitis Atypical forms of microscopic colitis Increased surface intraepithelial lymphocytes (IELs) with surface epithelial damage, normal crypt architecture with increased cryptal IELs, and (3) increased lamina propria inflammatory cell infiltrate including lymphocytes, plasma cells, and eosinophils. Thickened sub-epithelial collagen band. This finding is not present in lymphocytic colitis and consists of a linear deposition of dense collagen in the sub-epithelial area with an additional finding of cells, fibroblasts, and capillaries entrapped in the collagen Cryptal Lymphocytic Colitis the main feature of lymphocytic colitis is the intraepithelial lymphocytosis in surface epithelium Paucicellular Lymphocytic Colitis increased lamina propria lympho-plasmacytic inflammation and increased surface intraepithelial lymphocytes alternating with foci or tissue fragments of normal mucosa Microscopic Colitis With Giant Cells the main feature of lymphocytic colitis is the intraepithelial lymphocytosis in surface epithelium. Microscopic Colitis With Giant Cells atypical form of microscopic colitis characterized by the presence of multinucleated giant cells in an otherwise classic microscopic colitis Pseudomembranous Collagenous Colitis collagenous colitis associated with pseudomembranes Microscopic Colitis with Granulomatous Inflammation atypical form of microscopic colitis with a conspicuous granulomatous reaction.

Table 2: Histological classification of microscopic colitis.