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Adenoma is a non cancerous tumor that begins in the epithelium of mucosa or in the glands and ducts of the endocrine (hormone producing glands) or exocrine glands (like sweat glands and glands in the breasts).
Naked eye appearance of an adenoma varies depending on the site of origin. For example adenomas that affect hollow organs like the tube-like colon or gut shows that growth of the adenoma or tumor into the lumen or hollow. This is termed an adenomatous polyp or polypoid adenoma.
If this tumor has a broad base it is called sessile and if it has a narrow slender neck with a bulbous head, it is called pedunculated.
Adenomas that affect glands and solid organs like the thyroid, adrenal, pituitary, kidneys, breasts etc. have a ball like growth with no definite well defined particular shape.
Like any tumor, adenoma cells show some changes in their cellular architecture. This is also known as loss of normal differentiation or maturity of epithelium or epithelial cells. This change is termed cell dysplasia or atypia.
The cells become tube like (tubular), finger like (villous) or both (tubule-villous). The cells of the tumor appear irregular with deep colored (hyperchromatic) and stratified nucleus and nucleolus, decreased secretion of mucus and cell division states (mitosis).
Since adenomas are not cancers yet, the basement membrane is intact as is the muscularis mucosae.
In colonic adenomas there is low grade cellular dysplasia. There may be reduced intracellular mucin secretion as well. The nucei are larger with stratification and there are several mitoses or cell divisions. After dadenoma, the tumors may progress to adenocarcinoma in situ followed by dysplastic carcinoma.
In papillary adenomas of the kidney the cells appear tubular and the adenomas are less than 0.5cm. They are of low grade. These adeniomas contain tubular cells and papillary cells lined by cuboidal cells. There may be little or no atypia.
In breast fibroadenomas there are both epithelial and stromas components. Cellular changes are noted in the epithelial component. Adenomas of the thyroid are macroscopically small and discrete masses. They are mainly derived from follicular epithelium and are called follicular adenomas.