Knuckle sign (pulmonary embolism)

Knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to embolus. It is better visualised on CT pulmonary angiography scan than chest x-ray. This is an important ancillary finding in pulmonary embolism (PE), and often associated with the Fleischner sign of dilated central pulmonary arteries. 

It is one of several described signs of pulmonary embolus on chest radiographs.

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Article information

rID: 41201
System: Chest
Section: Signs
Synonyms or Alternate Spellings:
  • Knuckle sign: pulmonary embolism
  • Knuckle sign in pulmonary embolism

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