Silhouette sign (x-rays)
Updates to Article Attributes
Silhouette sign is somewhat of a misnomer and in the true sense actually denotes the loss of a silhouette, thus, it is sometimes also known as loss of silhouette sign or loss of outline sign 4.
The differential attenuation of x-ray photons by two adjacent structures defines the silhouette, e.g. heart borders against the adjacent lung segments, and it is the pathological loss of this differentiation, which the silhouette sign refers to. In short, it denotes that a mediastinal border can only be obscured by pathology which is in direct anatomical contact
Radiographic appearance
Plain radiograph
Recognition of this sign is useful in localising areas of airspace opacities, atelectasis or mass within the lung, with the loss of these normal silhouettes on frontal chest radiographs being generally indicative of the site of pathology 3,4:
- right paratracheal stripe: right upper lobe
- right heart border: right middle lobe or medial right lower lobe
- right hemidiaphragm: right lower lobe
- aortic knuckle: left upper lobe
- left heart border: lingular segments of the left upper lobe
- left hemidiaphragm or descending aorta: left lower lobe
Sites of silhouette sign on the lateral chest radiograph include 3:
- posterior border of the heart +/- posterior left hemidiaphragm: left lower lobe
- anterior right hemidiaphragm: right middle lobe
- posterior right hemidiaphragm: right lower lobe
The silhouette sign forms the basis of the hilum overlay sign, cervicothoracic sign and thoracoabdominal sign 2.
History and etymology
Dr. Benjamin Felson (1913-1988) and, his brother Dr. Henry Felson(1907-1998), were American radiologists who popularised this sign 1. However it was the Drs. FelsonsFelson themselves themselves who state that Dr H. Kennon Dunham (1872-1944), an American chest physician and radiologist, was the first to describe the sign 15 years earlier (late-1920s) 1,5.
Differential diagnosis
The presence of a silhouette sign may not be due to intrapulmonary disease. For example 3,4:
- right heart border: pectus excavatum
- posterior border of heart (lateral projection): hiatus hernia
-</ul><p>The silhouette sign forms the basis of the <a href="/articles/hilum-overlay-sign">hilum overlay sign</a>, <a href="/articles/cervicothoracic-sign-1">cervicothoracic sign</a> and <a href="/articles/thoracoabdominal-sign">thoracoabdominal sign</a> <sup>2</sup>. </p><h4>History and etymology</h4><p><strong>Dr. Benjamin Felson </strong>(1913-1988) and, his brother <strong>Dr. Henry Felson</strong>, were American radiologists who popularised this sign <sup>1</sup>. However it was the <strong>Drs. Felsons</strong> themselves who state that <strong>Dr H. Kennon Dunham</strong> (1872-1944), an American chest physician and radiologist, was the first to describe the sign 15 years earlier (late-1920s) <sup>1,5</sup>.</p><h4>Differential diagnosis</h4><p>The presence of a silhouette sign may not be due to intrapulmonary disease. For example <sup>3,4</sup>:</p><ul>- +</ul><p>The silhouette sign forms the basis of the <a href="/articles/hilum-overlay-sign">hilum overlay sign</a>, <a href="/articles/cervicothoracic-sign-1">cervicothoracic sign</a> and <a href="/articles/thoracoabdominal-sign">thoracoabdominal sign</a> <sup>2</sup>. </p><h4>History and etymology</h4><p><strong>Dr. Benjamin Felson </strong>(1913-1988) and, his brother <strong>Dr. Henry Felson </strong>(1907-1998), were American radiologists who popularised this sign <sup>1</sup>. However it was the <strong>Drs. Felson</strong> themselves who state that <strong>Dr H. Kennon Dunham</strong> (1872-1944), an American chest physician and radiologist, was the first to describe the sign 15 years earlier (late-1920s) <sup>1,5</sup>.</p><h4>Differential diagnosis</h4><p>The presence of a silhouette sign may not be due to intrapulmonary disease. For example <sup>3,4</sup>:</p><ul>
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