Human infection with Echinococcus granulosus leads to the development of one or more hydatid cysts located mainly in the liver and lungs. Less frequently involved sites include kidneys, bones, spleen, muscles, central nervous system and eyes. The photograph shows a large hydatid cyst in the liver of a 31 y/o male. The cyst is thick-walled and contains collapsed folded membranous structures. The cysts grow slowly and the asymptomatic incubation period can last for years. Eventually, the pressure exerted on surrounding tissues may produce symptoms and signs which depend upon the location of the hydatid cyst. Non-specific signs include anorexia, weight loss, and weakness. Hydatid cysts located in liver may cause abdominal pain, nausea, and vomiting. Image copyright : pathorama.ch.