Hilum overlay sign

Hilum Overlay Sign

The hilum overlay sign is a radiological sign used in the interpretation of chest radiographs. It is particularly useful in distinguishing between a mass that is located in the lung and one that is located in the mediastinum. This sign is based on the observation of the hilum of the lung on a frontal chest X-ray.

A chest radiograph showing a fibrous tumor of the pleura, which may demonstrate the hilum overlay sign.

Anatomy of the Hilum

The hilum of the lung is the region where the bronchi, blood vessels, lymphatics, and nerves enter and exit the lung. It is located on the medial aspect of each lung and is a critical area in the interpretation of chest radiographs. The hilum is composed of the pulmonary artery, pulmonary veins, and the main bronchus.

Radiological Appearance

On a frontal chest X-ray, the hilum appears as a complex shadow due to the overlapping of various structures. The hilum overlay sign is observed when a mass is present in the mediastinum but does not obscure the normal contours of the hilum. This indicates that the mass is not in the lung itself but rather in the mediastinum.

Clinical Significance

The hilum overlay sign is significant in differentiating between a mediastinal mass and a pulmonary mass. If the hilum can be seen through the mass, it suggests that the mass is located in the mediastinum. Conversely, if the hilum is obscured, the mass is likely within the lung.

This sign is particularly useful in the evaluation of conditions such as lymphadenopathy, mediastinal tumors, and other pathologies that may present as masses on chest radiographs.

Interpretation

To correctly interpret the hilum overlay sign, radiologists must have a thorough understanding of the normal anatomy and variations of the hilum. The presence of the sign can guide further diagnostic imaging, such as CT scans, to better characterize the nature and extent of the mass.

Related Pages

• Chest radiograph
• Mediastinum
• Pulmonary artery
• Lymphadenopathy