Echinococcal Cyst of the Liver

The liver is the most common location (95% of cases) for infection by Echinococcosis multilocularis, a tapeworm that is endemic in central and northern Europe, northern Asia, Japan, China, Turkey, and parts of North America. Dogs are the definitive hosts and humans, sheep, goats, and other herbivores serve as intermediate hosts. Humans are aberrant intermediate hosts who can develop slowly progressive and life-threatening tumorlike growths in the liver.

Ultrasound reveals an amorphous, heterogeneous, hyperechoic mass sometimes associated with central hypoechoic areas and irregular calcifications. Vascular or biliary invasion may also be seen.

CT has a high sensitivity and is used to determine vascular, biliary, or extrahepatic extension, all of which have implications for resectability. CT findings include an infiltrating mass with irregular margins and calcified or cystic components. Parts of the mass may enhance.

In uncertain cases, MR imaging may be performed to confirm the hypothesis and visualize the lesion in different planes. It is the best imaging procedure to demonstrate a cystic component. It helps establish vascular or biliary tree involvement as well as extrahepatic extension. Usually described as an ill-defined partially solid and partially cystic lesion, the appearance of alveolar echinococcosis at MR imaging was recently categorized into five types by Kodama et al (8). Multiple small cysts without a solid component are type 1 (4%), a solid component associated with small cysts is type 2 (40%), a solid component associated with irregular large cysts is type 3 (46%), a solid component with no cysts is type 4 (4%), and a large cyst without a solid component is type 5 (6%). According to this classification, our case would correspond to type 1. Alveolar echinococcosis is reported to exhibit variable signal intensities on T1- and T2-weighted images and to demonstrate slight enhancement on gadolinium-enhanced images (8,9). The cystic, necrotic, and fibrotic component appears hypointense compared with the liver parenchyma on T1-weighted images. T2-weighted images are useful to detect small cysts and, as in our case, to localize extrahepatic cysts (8,9).

References

• Hosch W, Stojkovic M, Jänisch T, Kauffmann GW, Junghanss T. The role of calcification for staging cystic echinococcosis (CE). Eur Radiol. 2007 Oct;17(10):2538-45.
• Proietti S, Abdelmoumene A, Genevay M, Denys A. Echinococcal cyst. Radiographics. 2004 May-Jun;24(3):861-5.