Liver & intrahepatic bile ducts
Infectious nonviral
Echinococcal cyst

Topic Completed: 1 May 2012

Minor changes: 25 September 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Echinococcal cyst[TI] liver

Komal Arora, M.D.
Page views in 2020: 5,508
Page views in 2021 to date: 403
Cite this page: Arora K. Echinococcal cyst. website. Accessed January 23rd, 2021.
Definition / general
  • 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
  • 60 - 70% in liver, also brain, lung, other sites
  • Frequently communicates with biliary tract
  • 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
Echinococcus granulosus
Definition / general
  • 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

  • PAIR: puncture of cysts percutaneously, aspiration of fluid, introduction of protoscolicidal agent, reaspiration) plus antiparasitic drugs to minimize risk of anaphylaxis

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

Gross images

Images hosted on other servers:

Hydatid cyst with fluid and daughter cysts

Microscopic (histologic) description
  • 3 layers in cyst wall:
    1. 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
    2. Laminated membrane beneath germinal layer is 1 mm thick, avascular, eosinophilic, refractile and chitinous; strongly PAS+, GMS+
    3. Outer layer is dense fibrovascular tissue with chronic inflammatory cells, variable calcification develops after 5+ years

Microscopic (histologic) images

Images hosted on other servers:

Daughter cysts with germinal layer and scolices

Echinococcus multilocularis
Definition / general
  • Less common, slower growing than E. granulosus
  • Restricted to Northern Hemisphere
  • More tissue invasive than E. granulosus and may simulate malignancy or cirrhosis

  • Radical surgery

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

Microscopic (histologic) description
  • Thin laminated layer, only 10% have brood capsules and protoscolices
  • Usually no / minimal germinal layer
Back to top
Image 01 Image 02