By this name is meant a tumour composed of a congeries of exaggerated papillae like those of the skin, or like the villi of mucous membranes. A papilla or villus consists of a basis of connective tissue in which there is a loop of capillary blood-vessel, and a covering of epithelium. The epithelium is like that of the surface concerned, and may be stratified or in a single layer.
Their commonest situation is the skin, where they form the Wart, which is an overgrowth of a group of existing papillae covered with hard epidermis. At the surface of the wart the papillae may be covered over with a continuous layer of epidermis, or the individual papillae may project independently. The Horn is also formed on the basis of a group of papillae, but the hard horny epidermis is greatly developed, and forms a consistent outgrowth of considerable dimensions. The Condyloma is a syphilitic outgrowth due to exaggeration of the papillae, with very soft epidermis. It occurs near the genital organs mostly.
Fig. 90. - From a psammoma of the brain substance. Globular particles of brain sand are shown.
The ordinary wart is to be distinguished from the Congenital soft warts and Moles. These are often pigmented and sometimes covered with hairs. In their structure they not uncommonly contain tissue composed of round or spindle-shaped cells and so differ altogether from the true warts. It is these soft warts and moles which in after life are liable to give rise to sarcomas or cancers.
On mucous membranes papillomas may be gathered into local tumours or cover a considerable surface, giving it a shaggy villous appearance. In the larynx (Fig. 91) they often form localized prominent tumours, especially on the vocal cords. They are not uncommon in the rectum. In the urinary bladder they are of considerable importance on account of their tendency to haemorrhage. In this situation they may form distinct tumours with long branched papillae, or there may be a large surface which is simply villous in appearance. The papillae are covered with delicate epithelium, and severe and frequent haemorrhages are common.
Fig. 91. - Papilloma of larynx: e epithelium; h, connective tissue; g, mucous glands;/, an atrophied gland, x 20. (Cornil. and Ranvier).
The Pacchionian bodies of the arachnoid are really papillary formations, and Dr. Cleland has described tumours of this region which seemed to arise by extreme hyperplasia of these papillae.
Cleland, Glas. Med. Jour., 1851.