Liver and intrahepatic bile ducts - nontumor
Infectious (nonviral) disorders
Echinococcal cyst

Author: Komal Arora, M.D. (see Authors page)

Revised: 2 November 2017, last major update May 2012

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Echinococcal cyst[TI] liver

Cite this page: Arora, K. Echinococcal cyst. PathologyOutlines.com website. http://pathologyoutlines.com/topic/liverechinococcal.html. Accessed December 14th, 2017.
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
Sites
  • 60 - 70% in liver, also brain, lung, other sites
  • Frequently communicates with biliary tract
Laboratory
  • 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


Treatment
  • 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


Treatment
  • 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