The heart is the main visible structure in the mediastinum
Important diseases change the appearance of the aortic knuckle, the descending aorta, the aortopulmonary window, and the right paratracheal stripe
The heart is located in the middle mediastinum. Other visible structures of the mediastinum should also be checked when viewing a chest X-ray. These include the aortic knuckle, descending aorta, aortopulmonary window, and right paratracheal stripe.
Some structures of the mediastinum are not visible on a chest X-ray, for example the oesophagus (posterior mediastinum), great vessels (superior mediastinum), and thymus (anterior mediastinum).
From the level of the clavicles to the azygos vein the right edge of the trachea is seen as a thin white line or 'stripe'
This stripe is created by air of low density (blacker) lying either side of the comparatively dense (whiter) tracheal wall
Thickening of the paratracheal stripe (normally less than 3 mm) may represent pathology such as a paratracheal mass or enlarged lymph nodes
The left side of the trachea is not so well defined because of the position of the aortic arch and great vessels
Assessing the mediastinal contours
Whenever you look at a chest X-ray it is well worth looking for abnormalities in the region of the aortic knuckle, the aortopulmonary window, and the right paratracheal stripe.
Appreciation of the range of normal appearances of these structures will come with viewing as many chest X-rays as you can.
