The ruptured pulmonary hydatid cyst.

Abstract

Intact hydatid cysts of the lung, single or multiple, cannot be distinguished from neoplasms on roentgen examination (1). After rupture of a cyst and discharge of its fluid content, both the clinical and the roentgen picture change abruptly. The torn hydatid becomes infected; the parasite dies; the cough, fever, and expectoration indicate a pulmonary infection. The collapsed endocyst wall, which is retained, presents a characteristic appearance, simplifying the x-ray diagnosis. About one-half of our patients are seen after rupture of a cyst. Echinococcosis is caused by a parasite whose life cycle requires two hosts: a canine and a grazing animal, usually the dog and the sheep. The adult parasite, a minute tapeworm, lives in the dog's small intestine. Infested dogs defecate millions of ova, contaminating pastures and watering places. Grazing animals and also man ingest the ova, becoming the reservoir host of the larva. The eggs hatch in the duodenum and the larvae penetrate the intestinal wall, entering the circulation. Most of them are caught in the liver, some in the lungs. Those that pass these two sieves may reach the spleen, kidney, brain, or skeleton. A few escape destruction by the body tissues and develop into cysts, sometimes of great size. In the lung and liver a shell of compressed and fibrotic host tissue, the ecto- or pericyst, surrounds the hydatid (Fig. 1, A). The hydatid cyst is filled with clear fluid. An outer, tough, noncellular, lamina ted layer is lined by an inner membrane of germinal epithelium. These two layers, both parasitic in origin, form the wall of the endocyst. From the germinal zone scolices (Fig. 1, B) and daughter cysts proliferate. When an infected animal is slaughtered and the diseased viscera are fed to dogs, the cycle of the parasite is completed. When man is infected, the parasite is detoured down a blind alley with no possibility of transmission to dogs. The scolices eaten by the dog attach themselves to the intestinal mucosa, coating it like fur as they develop into adult tapeworms, gravid with ova. In the Near East a considerable endemic focus of hydatid disease exists. Pipkin (2) found that of 237 stray dogs collected in the streets of Beirut in the summer of 1948 one-third carried Taenia echinococcus. Neighboring Arab countries have similar infestations. In Fars, an arid province in South Iran, where sheep and goats are raised by both villagers and nomads, the disease is common. Of 5,530 sheep and goats examined in 1957 at the Shiraz municipal abattoir, 13.7 per cent were infected (9.7 per cent liver, 4 per cent lung). Of 45 stray dogs autopsied in the experimental surgery laboratory at the Nemazee Hospital in the same year, 13 had the tapeworms in the terminal ileum (3). The sheep-raising areas of Australia, New Zealand (4), and South America have not yet eradicated the disease. In North America two endemic foci exist, one in Alaska and northwest Canada among caribou, moose, elk, and reindeer (5).