Chest X-ray Anatomy
Hilar structures

Key points

  • 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.

Normal hilar position

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Normal hilar position

  • Each hilar point is the angle formed where the upper and lower lobe pulmonary vessels meet
  • They are useful points of reference to determine the position of the hila
  • Commonly the left hilum is higher than the right
  • Note: Not every normal patient has a clearly-defined hilar point on both sides

Pulmonary arteries

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Pulmonary arteries

  • 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.

Page author: Salisbury NHS Foundation Trust UK (Read bio)

Last reviewed: February 2020