Hydatid cysts occur secondary to infection with a parasitic worm of the genus Echinococcus. These cysts are most commonly found intrahepatically but may also be seen in the lungs and other solid viscera such as the spleen.

They characteristically are quite large, with mixed attenuation within (depending on the composition of the cyst fluid) and will often demonstrate peripheral calcification of the wall, with or without septations, daughter cysts within the parent cyst and/or satellite cysts. Their walls demonstrate contrast enhancement on both CT and MRI.