The knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to an embolus. It is better visualized on CT pulmonary angiography (CTPA) 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.
- 1.Kumaresh A, Kumar M, Dev B, Gorantla R, Venkata Sai P M, Thanasekaraan V. Back to Basics - 'Must Know' Classical Signs in Thoracic Radiology. J Clin Imaging Sci 2015;5:43
- 2.Geoffrey B. Marshall, Brenda A. Farnquist, John H. MacGregor et-al. Signs in Thoracic Imaging. J Thorac Imaging 2006;21:76–90
- 3.Williams JR, Wilcox WC. Pulmonary embolism: roentgenographic and angiographic considerations. AJR Am J Roentgenol. 1963; 89:333.
- 4. Abbas A, St Joseph EV, Mansour OM et-al. Radiographic features of pulmonary embolism: Westermark and Palla signs. Postgrad Med J. 2014;90 (1065): 422-3. doi:10.1136/postgradmedj-2013-132000 - Pubmed citation