A papilloma is a benign tumor composed of projections of fibrous connective tissue that are covered by one or more layers of epithelium, either squamous or columnar in type.

May be divided into the hard and the soft papilloma.

The hard occur on the skin as warts, and when so situated are commonly pigmented; also around the genitalia as a result of constant irritation, in which situation they are known as "venereal warts." Are also found on the true vocal cords in the larynx. Are covered by squamous epithelium which commonly undergoes keratosis, a horny change. In this form the "pearly bodies" or "epithelial pearls" are frequently found. These are made up of cells concentrically arranged, many of which have lost their nuclei and have become transformed into keratin. They are found only in squamous epithelium.

Papillomas covered by squamous epithelium are frequently found in the urinary bladder, and, although histologically benign, they very frequently undergo malignant changes.

Fig. 55. - Tuft of Papilloma of the Bladder (Stengel).

The soft papillomas occur in the intestine, and are covered by columnar epithelium. This form quite frequently undergoes malignant transformation.

The connective-tissue stalks may be simple projections or very complicated, branching outgrowths. They contain blood-vessels and lymphatics.

An adenoma is a tumor that in its structure resembles an epithelial gland. It is frequently very difficult to tell whether it is a true growth or only an enlargement of a normal gland.

Fig. 56. - Papillary Adenoma from the Rectum. Hemat.-eosin.

X 98 (Dürck). 1, Vascular stroma; 2, stratified cylindric epithelium.

Fig. 57. - Alveolar Adenoma of the Mammary Gland. Oc. 2; ob. 9 (McFarland).

In the new growth the tissues, though arranged typically, do not carry on any useful function. The secretion may be imperfect or there may be no duct through which it can escape.

Adenomas arise from epithelial glands, are circumscribed, encapsulated and rounded, or nodular. Have been found in all glandular tissues.

Fig. 58. - Flbro-Adenoma Of The Mammary Gland (Canalicular Form). Oc. 2; ob. 3 (McFarland).

Microscopically they consist of a framework of connective tissue, the meshes of which are covered by one or two layers of epithelial cells that resemble in shape and size those of the normal glands. The important point that distinguishes these growths from malignant ones is the relation of the cells to the basement membrane. In the benign adenoma the membrane is preserved and the cells show no tendency to invade the surrounding tissue.

If the connective tissue and epithelium are in normal proportion the growth is called a simple adenoma; if the connective tissue predominates, a fibro-adenoma.

If the tumor has a pedicle, it is known as an adenomatous polyp.

Fig. 59. - Adrenal Tumor from the Kidney (Hypernephroma).

(Dürck).

1, Large polygonal cells, containing an abundance of fat and arranged in tubes; 2, connective-tissue cells in the scanty stroma.

Through degenerations, particularly colloid or mucoid, an adenoma may become very large through cystic formation. It is then called an adenocystoma.

If villi extend into the acini in the above form the growth is called an adenocystoma papilliferum.