Infection of humans caused by larval stage of Echinococcus granulosus or Echinococcus multilocularis

Best diagnostic clue: Membranes ± daughter cysts in complex heterogeneous mass

E. granulosus

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  Anechoic cyst with double echogenic lines separated by hypoechoic layer

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  Honeycomb cyst, multiple septations

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  Water lily sign: Complete detachment of membrane

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  Snowstorm pattern: Anechoic cyst with internal debris and hydatid sand

E. multilocularis

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  Single/multiple echogenic lesions

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  Irregular necrotic lesions with microcalcifications

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  Ill-defined infiltrative solid masses

Hemorrhagic or infected cyst

Complex pyogenic abscess

“Cystic” metastases

Biliary cystadenocarcinoma

Caused by larval stage of Echinococcus tapeworm

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  E. granulosus

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    Most common form of hydatid disease, unilocular

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  E. multilocularis

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    Less common but aggressive

Serologic test positive in > 80% of cases

Rule out other complex or septate cystic liver masses

Imaging clue: Daughter cysts can float freely within mother cyst

Altering patient’s position may change position of daughter cysts