Posterior tracheal stripe

The posterior tracheal stripe (or line) is formed by air in the trachea and air in the right lung outlining the intervening posterior wall of the trachea and soft tissue. It is seen on lateral chest x-rays and normally measures less than 2.5 mm in width . Abnormal thickening has a variety of causes :

• congenital or acquired aortic arch abnormalities (most common)
• esophageal pathology: e.g. malignancy, dilatation, diverticula, duplication cysts, etc.
• mediastinitis 
• mediastinal hematomas

The posterior tracheal stripe can also normally appear thickened, measuring up to 5.5 mm, and is then called the tracheo-oesophgeal stripe and is formed by the interface of the posterior wall of the trachea with the anterior wall of the esophagus (instead of the right lung) .

The posterior tracheal stripe/tracheo-esophageal stripe forms the anterior border of the retrotracheal space.

Radiographic features

Plain radiograph

• appears as a vertical stripe posterior to the tracheal air column extending from the thoracic inlet to the tracheal bifurcation on lateral chest x-rays