Hepatic hydatid infection
Updates to Article Attributes
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
Pathology
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). There are two forms of E. granulosus:
- pastoral: most common form; dog is a main host
- sylvatic: wolf or dog is a main host
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.
Radiographic features
Plain radiograph
May show a curvilinear or ring calcific shadow overlying the liver due to calcification of the pericyst.
Ultrasound
AppearencesMultiseptate cyst with "daughter" cysts and echogenic material between cysts. Appearences can vary. May show a double echogenic shadow due to the pericyst. The The stage of the cyst may be classified on ultrasound, see: World Health Organization 2001 classification of hepatic hydatid cysts.
CT
Fluid density cyst, with frequent peripheral focal areas of calcification, usually indicates no active infection if completely circumferential. Septation Septation and daughter cysts may be visualised, Water lily sign: Cyst with floating, undulating membrane and detached endocyst. Fluid is of variable density depending on the amount of proteinaceous debris. May May also show hyperdense internal septa representing a spoke wheel pattern within a cyst.
Fluid is of variable density depending on the amount of proteinaceous debris.
may show dilated intrahepatic bile duct due to compression or rupture of cyst into bile ducts
MRI
- T1: mixed low signal (depending on the amount of proteinacous cellular debris)
- T1 C+ (Gd): the walls and septa enhance
- T2: mixed high signal (depending on the amount of proteinacous cellular debris), septa and daughter cysts are well visualised (especially on single shot T2 sequences)
Complications
Rupture
- 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).
Radiographic features
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
-</ul><p><em>E. multilocularis </em>definitive host (adult parasite) is the Red Fox (<em>Vulpes vulpes</em>), (sometimes cats and dogs as well) with humans as the accidental intermediate host. It is widely distributed throughout the northern hemisphere.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><p>May show a curvilinear or ring calcific shadow overlying the liver due to calcification of the pericyst.</p><h5>Ultrasound</h5><p>Appearences can vary. May show a double echogenic shadow due to the pericyst. The stage of the cyst may be classified on ultrasound, see: <a href="/articles/world-health-organization-2001-classification-of-hepatic-hydatid-cysts">World Health Organization 2001 classification of hepatic hydatid cysts</a>.</p><h5>CT</h5><p>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.</p><h5>MRI</h5><ul>- +</ul><p><em>E. multilocularis </em>definitive host (adult parasite) is the Red Fox (<em>Vulpes vulpes</em>), (sometimes cats and dogs as well) with humans as the accidental intermediate host. It is widely distributed throughout the northern hemisphere.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><p>May show a curvilinear or ring calcific shadow overlying the liver due to calcification of the pericyst.</p><h5>Ultrasound</h5><p>Multiseptate cyst with "daughter" cysts and echogenic material between cysts. Appearences can vary. May show a double echogenic shadow due to the pericyst. The stage of the cyst may be classified on ultrasound, see: <a href="/articles/world-health-organization-2001-classification-of-hepatic-hydatid-cysts">World Health Organization 2001 classification of hepatic hydatid cysts</a>.</p><h5>CT</h5><p>Fluid density cyst, with frequent peripheral focal areas of calcification, usually indicates no active infection if completely circumferential. Septation and daughter cysts may be visualised, Water lily sign: Cyst with floating, undulating membrane and detached endocyst. May also show hyperdense internal septa representing a spoke wheel pattern within a cyst.</p><p>Fluid is of variable density depending on the amount of proteinaceous debris. </p><p>may show dilated intrahepatic bile duct due to compression or rupture of cyst into bile ducts</p><h5>MRI</h5><ul>
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