Cardiac radiography

Changes in cardiac contours in lung collapse

Pulmonary parenchymal pathology directly affects the visualization of the cardiac silhouette. Because mediastinal structures are no longer adjacent to aerated lung tissue, their borders lose sharpness (the silhouette sign).

• Collapse of the left upper lobe: On a plain chest radiograph, the left heart border, aortic arch, and mediastinal contour become indistinct. With marked collapse, the apical segment of the lower lobe undergoes compensatory hyperinflation, and the aortic arch paradoxically becomes visible again. The Luftsichel sign (Luftsichel sign)—an air crescent between the collapsed lung and the aortic arch—may also be identified.
• Collapse of the lingular segment (lingular segment): Visualized as an opacity that closely abuts the left heart border.
• Collapse of the right middle lobe: The collapsed lobe is adjacent to the right heart, causing the right border to lose sharpness. If the collapse is parallel to the X-ray beam, a sail-shaped triangular shadow is visible near the heart border.

Pericardial effusion

Normally, the pericardial cavity contains 15–35 ml of fluid. A volume exceeding 50 ml is considered pathological. Causes may include infections, heart, renal, or liver failure, as well as neoplastic processes (lymphoma, breast or lung cancer).

On a conventional chest radiograph (CXR), effusion is reliably detected at volumes of 200 ml or greater. Typical findings:

1. The cardiac silhouette symmetrically enlarges and assumes a characteristic flask-like shape (flask configuration).
2. The cardiophrenic angles become abnormally acute.
3. On the lateral view, the retrosternal clear space disappears, and fluid density separates the epicardial fat from the substernal fat.
4. On the posteroanterior view, a curvilinear radiolucency may appear along the left border.
5. The size of the shadow changes rapidly, while the pulmonary vascular pattern remains unchanged.

Severe acute effusion can lead to cardiac tamponade (cardiac tamponade)—fluid compresses the chambers, limits ventricular filling, and critically reduces cardiac output. This diagnosis is confirmed by echocardiography (diastolic collapse of the right ventricular free wall).

Pericardial cysts and diverticula

Benign masses also alter the radiographic appearance of the cardiac silhouette.

• Pericardial cysts (pericardial cysts): The most common benign lesions of the pericardium. They are usually asymptomatic. On a radiograph, they appear as a sharply outlined bulge of the cardiac contour, most often in the right cardiophrenic angle. On CT, this is a well-defined lesion with water attenuation that does not enhance with contrast. On MRI (T1-weighted), the signal is typically low but may be hyperintense if the fluid has a high protein content.
• Pericardial diverticulum: An outpouching of the parietal layer through defects in the fibrous layer. It is also most frequently localized on the right. It requires surgical management due to its tendency to grow.

Congenital defects and anomalies

Pericardial developmental anomalies are rare and frequently associated with other malformations.

• Partial pericardial agenesis: The posteroanterior view reveals a bulge of the second left cardiac arch and a deep cleft between the first and second arches.
• Pericardial defects: May be complete or partial. They lead to cardiac herniation or interposition of lung tissue between the aorta and pulmonary artery. On the radiograph, the cardiac shadow is shifted to the left.
• Patent ductus arteriosus (PDA): Frequently occurs in premature infants with respiratory distress syndrome receiving surfactant therapy (due to a left-to-right shunt reversal). Radiographically, it manifests as sudden cardiomegaly, left atrial enlargement (which elevates the left main bronchus), and pulmonary edema.

Class and exam questions

What else to study on this topic

• MRI semiotics of pericardial cysts depending on protein composition
• Echocardiographic signs of cardiac tamponade: chamber compression and right ventricular collapse
• Patent ductus arteriosus (PDA) in premature infants: hemodynamics and treatment
• Differential diagnosis of pericardial effusion and atelectasis on CT

Other topics in the «Chest Radiology» section

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