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[Gr. hydatis, watery vesicle]

1. A cyst formed in the tissues, esp. the liver, from the development of the larval stage of Echinococcus granulosus (one of the species of the dog tapeworm). The cyst develops slowly, forming a hollow bladder from the inner surface of which hollow brood capsules are formed. These may be attached to the mother cyst by slender stalks or may fall free into the fluid-filled cavity of the mother cyst. Scolices form on the inner surface of the older brood capsules. Older cysts have a granular deposit of brood capsules and scolices called hydatid sand. Hydatids may grow for years, sometimes to an enormous size. lbendazole, mebendazole, and praziquantel have been used to treat the disease. The cyst should be removed surgically or percutaneously drained.
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HYDATID CYST (orig. mag. ×500); SEE: echinococcosis
2. A small cystic remnant of an embryonic structure.
SEE: choriocarcinoma; SEE: hydatid mole

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