Malacoplakia

MALACOPLAKIA, malacoplakia (from Greek malakos—soft and plax—plate, plaque), French cystite en plaques, a specific, rather rare change in the mucous membrane of the urinary bladder, observed sometimes (more often in women) during cystitis. The term was proposed by Hansemann. Much less frequently than in the urinary bladder, this change is encountered on the mucous membrane of the ureters and renal pelves. The change consists of the appearance on the mucous membrane, mainly in the lower part of the bladder, of yellowish or brownish, soft, slightly protruding plaques of round or oval shape, ranging in size from a pinhead to a large pea. The plaques may lie isolated or merge with one another; sometimes they are surrounded by a red rim of hyperemic tissue. Microscopic examination reveals that the basis of the formation of these plaques lies in the accumulation in the connective tissue of the mucous membrane and in the submucosal layer of a large number of special large cells of round, oval, or polygonal shape, and in their protoplasm are found various inclusions (erythrocytes, leukocytes, hyaline droplets, laminated bodies giving reactions for lime and iron, bacteria). Among and around the clusters of these cells, there are manifestations of banal inflammation in the form of inflammatory hyperemia, edema, and infiltration; the epithelial covering of the mucous membrane in the area of the plaques is usually absent. If, on the one hand, there are no particular doubts regarding the nature of the large cells characteristic of malacoplakia in the sense of their belonging to wandering cells of the macrophage type, then, on the other hand, views on the etiology of malacoplakia are very contradictory. The least probable are the assumptions of some authors who consider malacoplakia to be a specific granuloma of unknown etiology or a special form of tuberculous lesion of the urinary bladder; also unconvincing are opinions about the primary significance of the penetration into the bladder mucosa of certain bacteria (e.g., colon bacillus). The most well-founded views are those of Hart and others, who believe that the plaques of large cells develop as a result of infiltration of the bladder mucosa by urine on the basis of preliminary cystitis with ulceration of the epithelial covering; the precipitation (due to the contact of altered urine with the tissue) of various sediments and salts results in the appearance of large macrophages.