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A benign epithelial neoplasm in which the tumor cells form glands or glandlike structures; usually well circumscribed, tending to compress rather than infiltrate or invade adjacent tissue. [adeno- + G. -oma, tumor]

- acidophil a. a tumor of the adenohypophysis in which cell cytoplasm stains with acid dyes; often growth hormone–producing. SYN: eosinophil a..

- ACTH-producing a. a pituitary tumor composed of corticotrophs that produce ACTH, often a basophilic a.; may give rise to Cushing disease or Nelson syndrome.

- adnexal a. an a. arising in, or forming structures resembling, skin appendages.

- adrenocortical a. a benign tumor of adrenal cortical cells; small unencapuslated nodules of adrenal cortex are probably localized areas of hyperplasia rather than adenomas; true adenomas are rare and may be symptomless or associated with Cushing syndrome or primary aldosteronism.

- apocrine a. SYN: papillary hidradenoma.

- basal cell a. a benign tumor of major or minor salivary glands or other organs composed of small cells showing peripheral palisading.

- basophil a. a tumor of the adenohypophysis in which the cell cytoplasm stains with basic dyes, often ACTH-producing.

- bronchial a. obsolete term once used to encompass carcinoid tumors, mucoepidermoid carcinoma, and adenoid cystic carcinoma. Cf.:bronchial mucous gland a..

- bronchial mucous gland a. a rare benign tumor arising from the mucous glands of bronchial mucosa.

- canalicular a. (ca-na-lik′oo-lar) a variant of monomorphic a. composed of double rows of epithelial cells in long cords.

- chromophobe a., chromophobic a. a tumor of the adenohypophysis whose cells do not stain with either acid or basic dyes.

- colloid a. a follicular a. of the thyroid, composed of large follicles containing colloid. SYN: macrofollicular a..

- embryonal a. a benign neoplasm in which the glandular epithelial elements are not fully differentiated, resembling immature tissue observed in embryonic development.

- eosinophil a. SYN: acidophil a..

- follicular a. an a. of the thyroid with a simple glandular pattern.

- Fuchs a. a benign epithelial tumor of the nonpigmented epithelium of the ciliary body, rarely exceeding 1 mm in diameter.

- gonadotropin-producing a. a rare type of pituitary a. that produces FSH and LH; its cells can be identified only by immunochemical techniques.

- growth hormone–producing a. an a. that produces the clinical picture of gigantism or acromegaly, although a third of the cells have no granules or are a mixture of acidophils and chromophobes; some tumors may secrete both growth hormone and prolactin; often an acidophil or eosinophil a..

- hepatic a. a benign tumor of the liver, usually occurring in women during the reproductive years in association with lengthy oral contraceptive use. The tumor is usually solitary, subcapsular, and large, composed of cords of hepatocytes with portal triads. SYN: hepatocellular a..

- hepatocellular a. SYN: hepatic a..

- Hürthle cell a. an uncommon type of thyroid tumor characterized by abundant eosinophilic cytoplasm containing numerous mitochondria. Often malignant with widespread metastases; rarely takes up radioiodine. SEE ALSO: Hürthle cell carcinoma. SYN: oncocytic a..

- invasive pituitary a. extensive infiltrates of the dura, bone, and sinuses.

- lactating a. an uncommon a. of the breast composed of tubuloacinar structures with pronounced secretory changes such as seen in pregnancy and lactation.

- macrofollicular a. SYN: colloid a..

- mammosomatotroph cell a. a rare prolactin- and growth hormone–producing pituitary a. composed of ultrastructurally monomorphic cells with both somatotrophic and lactotrophic differentiation.

- microfollicular a. a fetal a. of the thyroid composed of very small follicles and solid alveolar groups of thyroid epithelial cells.

- monomorphic a. a benign ductal neoplasm of the salivary glands, with a uniform epithelial pattern and lacking the chondromyxoid stroma of a pleomorphic a..

- nephrogenic a. a benign tumor of the urinary bladder or urothelial mucosa, composed of glandular structures resembling renal tubules.

- a. of nipple SYN: subareolar duct papillomatosis.

- null-cell a. an a. of the hypophysis composed of cells for which there is no overt evidence of hormone production, but which usually produces hypopituitarism and visual disturbances by compression of adjacent structures; approximately one third of these tumors have cells with abundant mitochondria (oncocytes) that are somewhat larger than the monocytic null cells. SYN: undifferentiated cell a..

- oncocytic a. SYN: Hürthle cell a..

- oxyphil a. SYN: oncocytoma.

- papillary cystic a. an a. in which the lumens of the acini are frequently distended by fluid, and the neoplastic epithelial elements tend to form irregular, fingerlike projections.

- papillary a. of large intestine SYN: villous a..

- pituitary a. a benign neoplasm of the pituitary generally arising in the adenohypophysis.

- pleomorphic a. SYN: mixed tumor of salivary gland.

- polypoid a. SYN: adenomatous polyp.

- prolactin-producing a. a pituitary a. composed of prolactin-producing cells; it gives rise to symptoms of nonpuerperal amenorrhea and galactorrhea (Forbes-Albright syndrome) in women and to impotence in men. SYN: prolactinoma.

- prostatic a. the growth in benign prostatic hyperplasia.

- renal cortical a. an a., usually small, sometimes found in the renal cortex incidentally at autopsy and derived from renal tubular tissue.

- sebaceous a. a benign neoplasm of sebaceous tissue, with a predominance of mature secretory sebaceous cells. Cf.:a. sebaceum.

- a. sebaceum archaic misnomer for a hamartoma occurring on the face, composed of fibrovascular tissue and appearing as an aggregation of red or yellow papules that may be associated with tuberous sclerosis; sebaceous glands may be present but are not increased. Cf.:sebaceous a.. SYN: Pringle disease.

- thyrotropin-producing a. a rare pituitary a. usually associated with hypo- or hyperthyroidism.

- tubular a. 1. a benign neoplasm composed of epithelial tissue resembling a tubular gland. 2. dysplastic polyp of the colonic mucosa which is considered a potential precursor of adenocarcinoma.

- undifferentiated cell a. SYN: null-cell a..

- villous a. frequently appears as a solitary, sessile, often large, tumor of colonic mucosa, although it can occur anywhere through the GI tract; composed of mucinous epithelium covering delicate vascular projections; malignant change occurs frequently; hypersecretion occurs rarely. Also known as a.. SYN: papillary a. of large intestine.

ad·e·no·ma .ad-ən-'ō-mə n, pl -mas also -ma·ta -mət-ə a benign tumor of a glandular structure or of glandular origin

ad·e·no·ma·tous -mət-əs adj

a benign tumour of epithelial origin that is derived from glandular tissue or exhibits clearly defined glandular structures. Adenomas may undergo malignant change (see adenocarcinoma). Some show recognizable tissue elements, such as fibrous tissue (fibroadenomas), while others, such as some bronchial adenomas, may produce active compounds giving rise to clinical syndromes (see argentaffinoma). Tumours in certain organs, including the pituitary gland, are often classified by their histological staining affinities, for example eosinophil, basophil, and chromophobe adenomas.