Double density sign (left atrium)
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The double-density sign, also known as the double right heart border, is seen on frontal chest radiographs in the presence of left atrial enlargement, and occurs when the right side of the left atrium extends behind the right cardiac shadow, indenting the adjacent lung and forming its own distinct silhouette 1-3.
If large enough, the left atrium can actually reach beyond the border of the right atrium; this is known as atrial escape 3. The right superior pulmonary vein can lead to a similar appearance 1.
- 1. Higgins CB, Reinke RT, Jones NE et-al. Left atrial dimension on the frontal thoracic radiograph: a method for assessing left atrial enlargement. AJR Am J Roentgenol. 1978;130 (2): 251-5. AJR Am J Roentgenol (abstract) - Pubmed citation
- 2. Webb WR, Higgins CB. Thoracic Imaging. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 3. Brant WE, Helms C. Fundamentals of Diagnostic Radiology. Lippincott Williams & Wilkins. (2012) ISBN:1608319113. Read it at Google Books - Find it at Amazon