Each hilum contains major bronchi and pulmonary vessels
Hilar lymph nodes are not visible unless abnormal
The left hilum is commonly higher than the right
Check the position, size and density of each hilum
The lung roots, or hila (singular – hilum), are complicated anatomical structures containing the pulmonary vessels and the major bronchi, arranged asymmetrically.
Although the hilar lymph nodes are not visible on a normal chest X-ray, they are of particular importance clinically. Often, hilar enlargement is due to enlargement of these nodes.
Many disease processes involve the hila, so a knowledge of their normal X-ray appearance is important. Both hila should be of similar size and density. If either hilum is bigger and more dense (whiter) than normal, this may indicate an abnormality.
Deoxygenated blood (blue arrows) is pumped upwards out of the right ventricle (RV) via the main pulmonary artery (Main PA)
The main PA divides into left pulmonary artery (Left PA) and right pulmonary artery (Right PA) which pass into the lungs via the hila
The left PA hooks backwards over the left main bronchus
The right PA passes anterior to the right main bronchus
Assessing the hila
Chest X-ray assessment routinely involves checking the hilar structures for normal, size, density and position. The hila are often wrongly called abnormal when normal and normal when abnormal. An awareness of the range of normal is important, but the best tip is to look for increase in density as well as size. If the hila are out of position, ask yourself if they are pushed or pulled, just as you would when assessing the trachea.
