The radiological appearances of hydatid disease of the liver

The liver is the most frequent site of Echinococcus granulosus cysts. The radiological features of 22 cases are described. The ultrasound and computed tomography (CT) appearances are emphasised and the literature is reviewed. Cysts can be single or multiple and appear uni- or multilocular. Calcification occurs in about a quarter of cases. The cyst wall is usually thin and well-defined but may be thick and can enhance on CT. Separation of the laminated membrane from the pericyst produces a 'split wall' appearance. Complete collapse of the laminated membrane results in an ultrasound 'water lily sign'. Daughter cysts are initially solid then become cystic. A fluid level can be due to hydatid sand but layering in a poorly defined cyst indicates an infected or complicated cyst. This paper does not deal with the appearances of liver disease due to Echinococcus multilocularis.