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Liver and intrahepatic bile ducts-nontumor

Infectious (non-viral) disorders

Echinococcal cyst


Reviewers: Komal Arora, M.D. (see Reviewers page)
Revised: 12 May 2012, last major update May 2012
Copyright: (c) 2004-2012, PathologyOutlines.com, Inc.

General
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● Most common cause of hepatic cysts worldwide, particularly in Middle East, Greece, Australia, North Africa, parts of South America
● In US, usually in immigrants from above areas
● Due to dog tapeworm in larval or cystic stage: E. granulosus (causes cystic hydatid disease), less commonly E. multilocularis (alveolar hydatid disease), or E. vogeli (polycystic hydatid disease)
● Definitive hosts are dogs, wolves, cats or other carnivores
● Intermediate or cystic stage usually affects sheep, hogs or cows, rarely man or other mammals

Laboratory
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● Serum assays for E. granulosus are 90% sensitive with occasional false positives
● High sensitivity and specificity for E. multilocularis
● Frequent eosinophilia if cyst is viable

Sites
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● 60-70% in liver, also brain, lung, other sites
● Frequently communicates with biliary tract


Echinococcus granulosus

General
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● Most common species of infection
● Cyst enlarges 1-5 cm per year; becomes symptomatic at 10 cm
● Cysts may be infectious or sterile, superficial or deep
Life cycle: protoscolices (future heads of adult tapeworm) develop within brood capsules; when brood capsules detach, are called daughter cysts

Treatment
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PAIR - Puncture of cysts percutaneously, Aspiration of fluid, Introduction of protoscolicidal agent, Reaspiration) plus antiparasitic drugs to minimize risk of anaphylaxis

Gross description
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● 75% solitary
● Unilocular cyst, white, fluid filled

Gross images
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Hydatid cyst with fluid and daughter cysts

Micro description
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● 3 layers in cyst wall:
● (a) innermost (germinal layer) is 10-25 microns, contains nuclei, gives rise to brood capsules attached by short stalk in infectious (fertile) cysts
● Often with daughter cysts
● Also protoscolices (attached or separated) with double row of refractile, birefringent, acid-fast hooklets 22-40 microns and 4 round suckers that comprise “hydatid sand”
● Daughter cysts may merge and provide internal septation
● (b) laminated membrane beneath germinal layer is 1 mm thick, avascular, eosinophilic, refractile and chitinous; strongly PAS+, GMS+
● (c) outer layer is dense fibrovascular tissue with chronic inflammatory cells, variable calcification develops after 5+ years

Micro images
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Daughter cysts with germinal layer and scolices


Echinococcus multilocularis

General
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● Less common, slower growing than E. granulosus
● Restricted to Northern hemisphere
● More tissue invasive than E. granulosus and may simulate malignancy or cirrhosis

Treatment
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● Radical surgery

Gross description
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● Alveolar structure with numerous irregular cysts 1-20 mm, appear infiltrative into adjacent liver, may have necrosis, calcification

Micro description
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● Thin laminated layer, only 10% have brood capsules and protoscolices
● Usually no/minimal germinal layer

End of Liver and intrahepatic bile ducts-nontumor > Infectious (non-viral) disorders > Echinococcal cyst


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