Cardiac silhouette

Cardiac silhouette refers to the outline of the heart as seen on frontal and lateral chest radiographs and forms part of the cardiomediastinal contour. The size and shape of the cardiac silhouette provide useful clues for underlying disease.

Radiographic features

From the frontal projection, the cardiac silhouette can be divided into right and left borders:

• the right border is formed by the right atrium
  • ​the superior vena cava entering superiorly and the inferior vena cava often seen at its lower margin
• the left border is formed by the left ventricle and left atrial appendage
  • ​the pulmonary artery, aortopulmonary window and aortic notch extend superiorly

On the lateral projection the cardiac silhouette is formed by :

• the anterior border by right ventricle
• the posterior border by left atrium (superiorly) and left ventricle (inferiorly) and the inferior vena cava

Size

The cardiac silhouette is considered enlarged if the cardiothoracic ratio is greater than 50% on a PA view of the chest . See main article: enlargement of the cardiac silhouette for more information.

Shape

The shape of the cardiac silhouette can be used as clues to the underlying disease. For example :

• a "water bottle" configuration occurs with pericardial effusion or generalized cardiomyopathy
• left ventricular or "Shmoo" configuration describes lengthening and rounding of the left heart border with a downward extension of the apex resulting from left ventricular enlargement
• "straightening" of the left heart border is seen with rheumatic heart disease and mitral stenosis