Adenoma is a benign epithelial tumor arising in epithelium of mucosa (stomach, small intestine and bowel), glands (endocrine and exocrine) and ducts. In hollow organs (e.g. digestive tract) the adenoma grows upwards into the lumen - adenomatous polyp or polypoid adenoma. Depending on the type of the insertion base, adenoma may be pedunculated (lobular head with a long, slender stalk, covered by normal mucosa - see photo) or sessile (broad base). If not elevated above the surface of the mucosa, the adenoma is called flat adenoma.
Adenomatous tubulo-villous polyp, pedunculated (colon). The adenomatous proliferation is characterized by different degrees of cell dysplasia (cellular and architectural atypia) : loss of normal differentiation of epithelium, irregular cells with hyperchromatic nuclei, (pseudo)stratified nuclei, nucleolus, decreased mucosecretion and mitosis. The architecture may be tubular, villous or tubulo-villous. Basement membrane and muscularis mucosae are intact.
Compared to normal colonic epithelium (lower left corner of the picture) the adenomatous proliferation is characterized by different degrees of cell dysplasia and tubular, villous or tubulo-villous architecture. In tubular component tumor cells proliferate generating tubular shapes, more or less irregular or branched. The villous pattern presents villi - finger-like projections lined by dysplastic epithelium and with thin fibro-vascular core. Passage from tumoral epithelium to normal mucosa is abrupt
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