Hepatic hydatid disease is a parasitic zoonosis caused by the Echinococcus tape worm. (see: Hydatid disease for a general discussion). In the liver, two agents are recognised as causing disease in the human:
- Echinococcus granulosus
- Echinococcus multilocularis
E. granulosus is endemic in North America and Australia, and is commonly seen in the liver. It typically forms spherical, fibrous rimmed cyst with little if any surrounding host reaction. Classically it has a large parent cyst within which numerous peripheral daughter cysts are present. Satellite daughter cysts (outside the parent cyst) are seen frequently (~16% cases).
E. multilocularis definitive host (adult parasite) is the Red Fox (Vulpes vulpes), (sometimes cats and dogs as well) with humans as the accidental intermediate host. It is widely distributed throughout the northern hemisphere.
May show a curvilinear or ring calcific shadow overlying the liver due to calcification of the pericyst.
Appearences can vary. May show a double echogenic shadow due to the pericyst. The stage of the cyst may be classified on ultrasound, see: World Health Organization 2001 classification of hepatic hydatid cysts.
Fluid density cyst, with frequent peripheral focal areas of calcification. Septation and daughter cysts may be visualised. Fluid is of variable density depending on the amount of proteinaceous debris. May also show hyperdense internal septa representing a spoke wheel pattern within a cyst.
- T1: mixed low signal (depending on the amount of proteinacous cellular debris)
- T1 C+ (Gd): the walls and septae enhance
- T2: mixed high signal (depending on the amount of proteinacous cellular debris), septae and daughter cysts are well visualised (especially on single shot T2 sequences)
- into biliary tree
- to peritoneal space (if exophytic)
- into blood stream
Hepatic alveolar echinococcosis (HAE)
Hepatic alveolar echinococcosis (HAE) (sometimes referred to as E. alveolaris - although this is not the species name) is a rare cause of hepatic hydatid disease caused by Echinococcus multilocularis. It mimics a slow-growing tumour, as in contrast to E. granulosus it does not form a well defined encapsulated mass, but rather infiltrates the liver and its surrounding structures, especially at the porta hepatis (hepatic veins, inferior vena cava (IVC), and the biliary tree).
It usually presents as a large ~10 cm) multiloculated/confluent necrotic mass without a fibrous capsule. It has irregular margins with nodular components, but does not demonstrate central enhancment. Up to 38% of cases have peripheral liver reactive enhancement.
Differential diagnosis of HAE
- 1. Sréter T, Széll Z, Egyed Z et-al. Echinococcus multilocularis: an emerging pathogen in Hungary and Central Eastern Europe? Emerging Infect. Dis. 2003;9 (3): 384-6. Emerging Infect. Dis. (link) - Pubmed citation
- 2. Pedrosa I, Saíz A, Arrazola J et-al. Hydatid disease: radiologic and pathologic features and complications. Radiographics. 20 (3): 795-817. Radiographics (full text) - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Echinococcal liver disease||✓|
|Hepatic hydatid cyst||✗|
|Hepatic hydatid disease||✗|
|Liver hydatid disease||✓|
|Liver hydatid cyst||✗|