Anterior junction line

The anterior junction line is a feature on frontal chest radiographs (CXR), formed by the apposition of the visceral and parietal pleura of the anteromedial aspects of the lungs with a small amount of intervening mediastinal fat.The line consists of four layers of pleura and a variable amount of intervening fat.

The anterior junction line is the middle component of the anterior junction reflection. The V-shaped superior recess is the more cranial component and is formed by contact between the lungs and the retromanubrial mediastinal fat. The inverted V-shaped inferior recess is formed by separation of the lungs from intervening heart and mediastinal fat. 

Normal radiographic appearance: 

It appears as an oblique line crossing the superior two-thirds of the sternum from upper right to lower left. A small amount of mediastinal fat is normally found within the line; however, increased amounts of intervening mediastinal fat and possibly thymus in younger patients may cause the anterior junction line to appear as a stripe.

The posterior junction line has reportedly been seen on 24,5%-57% of posteroanterior chest radiographs.

Abnormal radiographic appearance: 

Because of the location of the anterior junction line in the anterior mediastinum, obliteration or abnormal convexity of the line suggests underlying anterior mediastinal disease such as thyroid masses, lymphadenopathy, neoplasms, thymic masses, or lipomatosis. Volume loss and hyperinflation of the surrounding lung can also displace the line.

The anterior junction line may occasionally look like a pneumomediastinum (this aspect is termed as pseudopneumomediastinum).