Hydatid cyst is an infestation caused by the larval form of Echinococcus granulosus. The disease is endemic in many areas (such as Mediterranean countries, South America, Australia, New Zealand, and East Africa) where sheep, dog, and man live in close contact. The adult tapeworm lives in the intestine of the dog, from which ova are passed into the stool. Humans may become infected through direct contact with infected dogs or through ingestion of food contaminated by ova. Chitinous envelopes of ova are dissolved by the gastric juice of intermediate hosts who have ingested the parasite's eggs. Embryos pass through the intestinal wall and are carried by the portal vein to the liver. The embryos become adult cysts in the liver. Most of the cysts are caught in the hepatic sinusoids; a few ova may pass through the liver, heart, and pulmonary capillaries and reach general circulation to lodge in such sites as the orbit, heart, thyroid gland, lung, bones, urinary bladder, and other internal organs.1