Chest x-ray anatomy

Hilar structures

The hila (lung roots) are complicated structures mainly consisting of the major bronchi and the pulmonary veins and arteries. These structures pass through the narrow hila on each side and then branch as they widen out into the lungs. The hila are not symmetrical but contain the same basic structures on each side.

Although the hilar lymph nodes are not visible on a normal chest x-ray, they are of particular clinical importance. Often, hilar enlargement is due to enlargement of these nodes.

Many disease processes involve the hila, and so a good knowledge of their normal x-ray appearance is important. There is, however, a wide range of normal. The hila may be at the same level, but commonly the left hilum is higher than the right. Both hila should be of similar size and density. If either hilum is bigger and more dense, this is a good indication that there is an abnormality.

Key points

  • Each hilum contains major bronchi and pulmonary vessels
  • There are also lymph nodes on each side(not visible unless abnormal)
  • The left hilum is often higher than the right
  • If a hilum is out of position, ask yourself if has been pushed or pulled
  • As well as position - check the size and density of the hila
Hover over image to show findings

The pulmonary arteries

Deoxygenated blood (blue arrows) is pumped upwards out of the right ventricle (RV) via the main pulmonary artery (MPA). This divides into left (LPA) and right (RPA) which each pass via the lung hila into the lung tissue to distribute blood for oxygenation.

On the left the LPA hooks backwards over the left main bronchus. On the right the RPA lies in front of the right main bronchus.

Click image to align with the top of the page
Hover over image to show findings
Click image to align with the top of the page

The hilar points

By convention the hilar points are the angle formed by the descending upper lobe veins, as they cross behind the lower lobe arteries. Not every normal patient has a very clear hilar point on both sides, but if they are present then they can be useful in determining the position of the hila.

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 vice-versa. 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.

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