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) or sessile (broad base - see photo). If not elevated above the surface of the mucosa, the adenoma is called flat adenoma.
Adenomatous villous polyp, sessile (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 atypical mitosis. The architecture may be tubular, villous (photo) or tubulo-villous. Basement membrane and muscularis mucosae are intact.
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