cardiovascular silhouette (radiology)

Last reviewed 01/2018

The cardiovascular silhouette is the radiodensity apparent on a standard PA chest radiograph due to the contrast of the blood-filled heart and great vessels against the surrounding air-filled lungs.

It has prominences on each border which occur in a regular sequence and represent cardiovascular structures:

• right border, from superior to inferior:
• superior vena cava
• right atrium
• inferior vena cava
• left border, from superior to inferior:
• arch of aorta - this prominence is termed the aortic knob
• pulmonary trunk
• left auricle
• left ventricle

Inferiorly, the heart shadow merges with that of the diaphragm.

The overall shape of the cardiovascular silhouette is dependent on the phase of breathing due to the attachments of fibrous pericardium to the diaphragm inferiorly. The pericardium is relatively fixed by the great vessels to the roots of the lungs superiorly, so descent of the diaphragm during inspiration tends to make the silhouette look thinner and longer. Hence, standardly chest films are taken in inspiration. Conversely, the normal variation within the population of the shape of the heart results both in extremes of very thin and broad silhouettes. The former are more common in the obese and pregnant ladies; the latter are more common in thin individuals.

Lateral radiographs reveal a radiolucent space posterior to the heart and anterior to the vertebral column; this is the retrocardiac space. It contains the oesophagus and descending aorta.