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Knuckle sign (pulmonary embolism)

Last revised by Dr Mostafa El-Feky on 15 Jan 2022

The knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to a pulmonary embolus (PE). It is better visualized on CT pulmonary angiography (CTPA) than chest x-ray. This is an important ancillary finding in pulmonary embolism, 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.

See also

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Cases and figures

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