A hydatid cyst is a fluid-filled sac caused by infection with the Echinococcus tapeworm, transmitted to humans through contact with infected dogs or contaminated food. The liver is the most commonly affected organ, followed by the lungs. On ultrasound, hydatid cysts have variable appearances depending on their stage of development, classified using the WHO ultrasound classification system. They can range from simple, anechoic cysts in early stages to complex cysts with internal daughter cysts, a floating membrane (water lily sign), or a solid, calcified mass in the final stage. The presence of daughter cysts within a larger cyst is highly specific for hydatid disease.
Sonography Term