Silhouette sign was described by Dr. Ben Felson. The silhouette sign is in essence elimination of the silhouette or loss of lung/soft tissue interface caused by a mass or fluid in the normally air filled lung. In other words, if an intrathoracic opacity is in anatomic contact with, for example, the heart border, then the opacity will obscure that border. The sign is commonly applied to the heart, aorta, chest wall, and diaphragm. The location of this abnormality can help to determine the location anatomically.
The lack of Silhouette sign indicates that there is air filled strucure (normal lung parenchyma) between the lesion and the heart in this case.
|note the small air-fluid level according to abscendation|