2001 WHO classification of hepatic hydatid cysts

The 2001 World Health Organization (WHO) classification of hepatic hydatid cysts is used to assess the stage of hepatic hydatid cysts on ultrasound and is useful in deciding the appropriate management for it depending on the stage of the cyst. This classification was proposed by the WHO in 2001 and, at the time of writing (July 2016), remains the most widely used classification for hepatic hydatid cysts.

  • CL
    • unilocular anechoic cystic lesion
    • no internal echoes or septations
  • CE 1 (active stage)
    • uniformly anechoic cyst with fine internal echoes, may only be visible after patient repositioning
    • internal echoes represent "hydatid sand" (fluid and protoscolices originating from a ruptured vesicle) 
  • CE 2 (active stage)
    • cyst with internal septation
      • septa represent walls of daughter cyst(s) 
      • described as multivesicular, rosette, or honeycomb appearance
  • CE 3 (transitional stage)
    • the evolving appearance of daughter cyst(s) within the encompassing parent cyst
    • 3A - daughter cysts have detached laminated membranes (water lily sign)
    • 3B - daughter cysts within a solid matrix
  • CE 4 (inactive/degenerative)
    • absence of daughter cysts
    • mixed hypoechoic and hyperechoic matrix, resembling a ball of wool (ball of wool sign)
  • CE 5 (inactive/degenerative)
    • arch-like, thick partially or completely calcified wall


  • CL: cystic lesion
  • CE: cystic echinococcosis