Imaging of hydatid disease with a focus on extrahepatic involvement

Hydatid disease (HD) is a parasitic infection caused by the larvae of a tapeworm that is endemic to many regions around the world—South America, Africa, and Asia, in particular. Humans are infected as intermediate hosts in the parasite’s life cycle; thus, HD can be seen in persons living in areas where animal husbandry is practiced. However, owing to the varied patterns of migration and immigration during the past several decades, HD can be diagnosed in individuals living anywhere. The liver is the most common organ involved, with hepatic HD accounting for the majority of published cases. However, HD can affect multiple organs and tissues other than the liver, including the spleen, kidneys, lungs, heart, peritoneum, muscles, and brain. Knowledge of the route of spread, clinical findings at presentation, and possible complications involving each extrahepatic location can be useful for the radiologist when evaluating imaging findings in patients suspected of having HD. The ultrasonographic, computed tomographic, and magnetic resonance imaging findings of extrahepatic hydatid lesions frequently simulate those of hepatic HD, as long as rupture, bleeding, and/or superimposed bacterial infection has not occurred. Specific features of HD seen at different extrahepatic sites can help tailor the diagnosis. The differential diagnoses that can mimic HD at every nonhepatic location should be considered, as many of these entities are common, especially in nonendemic areas.