Ball of wool sign (hydatid cyst)

The ball of wool sign, also referred to as the yarn sign or congealed water lily sign, is an ultrasound appearance, representing degeneration of hydatid cysts (WHO class CE 4). The inner side of cyst detaches from the cyst wall and folds on itself, causing a change from anechoic (fluid) to a solid, hyperechoic appearance without internal septations or daughter cysts 4.

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Article information

rID: 49542
Section: Signs
Synonyms or Alternate Spellings:
  • Spin sign
  • Whorl sign
  • Congealed water lily sign
  • Yarn sign

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