Azygoesophageal line

The azygoesophageal line (also called the azygoesophageal recess interface) is a mediastinal line seen on the frontal chest radiograph, representing the interface between the right lung and the mediastinal structures in the region of the azygos vein and esophagus.

Anatomical Basis

The azygoesophageal recess is the space where the right lower lobe of the lung contacts the subcarinal portion of the mediastinum specifically, the region bounded by the azygos vein posteriorly and the esophagus anteriorly. On a frontal chest radiograph, this contact produces a visible line or interface that extends vertically along the right side of the mediastinum, typically from the level of the azygos arch superiorly to the diaphragm inferiorly. The right posterior inferior lung margin is continuous medially with this recess in approximately 96% of cases.

Normal Appearance

In normal adults, the azygoesophageal line appears as a smooth, gently concave (leftward) contour on the frontal radiograph. On CT, the recess similarly has a concave configuration in adults. Notably, this configuration is age-dependent: in children younger than 3 years, a convex or straight contour is found in 96% of cases, and the typical adult concave configuration is not reliably seen until adolescence (>12 years).

Clinical Significance

The azygoesophageal line is one of the most sensitive mediastinal interfaces for detecting pathology. Disruption, displacement, or convexity of this line on a frontal chest radiograph can indicate disease in either the middle or posterior mediastinum. Common causes of abnormality include:

• Subcarinal lymphadenopathy (e.g., from lung cancer, lymphoma, sarcoidosis)

• Esophageal masses or dilation

• Bronchogenic or foregut duplication cysts

• Left atrial enlargement

• Hiatal hernia

• Descending aortic aneurysm