What Is the Hilum of the Lung?

Definition and Anatomy of the Hilum in the Lungs

diagram illustrating the location of the hilum in the lung
Hilum of the lung. istockphoto.com

Definition: Hilum of the Lung

The hilum is the wedge-shaped area on the central portion of each lung where the bronchi, the arteries, veins, and nerves enter and exit the lungs.

Anatomy of the Hilum

Both the right and the left lung have a hilum region which lies roughly midway down the lungs, and slightly towards the back. Each lung may be visualized as having an apex (the top) a base (the bottom) a root and a hilus.

The major bronchi, pulmonary arteries, pulmonary veins, and nerves are the structures which enter and exit the lungs in this region. Lymph nodes, called hilar lymph nodes, are also present in this region.  Both hilum are similar in size, with the left hilum usually found higher than the right.


On a chest x-ray, the hilar region reveals a shadow which consists of the combination of lymph nodes, the pulmonary arteries, and the pulmonary veins.

Abnormalities of the Hilum

This region of the lung may be affected by tumors in the region (including metastatic tumors) enlargement of hilar lymph nodes, as well as abnormalities of the pulmonary arteries or veins.  

Hilar Enlargement/Hilar Masses

There are 4 main reasons that the hilum of one or both lungs may appear enlarged on an x-ray.  These include:

  • Tumors and lymphadenopathy - Cancers such as lung cancer  and lymphomas, as well as cancer that has spread to this region from other parts of the body (metastatic cancer.)
  • Pulmonary venous hypertension (elevated pressure in the pulmonary veins) - This may occur with problems such as heart failure and heart valve problems such as mitral stenosis and mitral regurgitation.
  • Pulmonary arterial hypertension (PAH - elevated pressure in the pulmonary arteries) - PAH may occur as a primary disease (not secondary to another problem) or as a secondary problem which in turn is caused by chronic obstructive pulmonary disease (COPD.)
  • Increased pulmonary blood flow.

Hilar Lymphadenopathy (Enlarged Hilar Lymph Nodes)

Enlarged lymph nodes in the hilum may occur in both the right and left hilum (bilateral lymphadenopathy) or on side alone (asymmetric lymphadenopathy.) Causes may include:

Example: John was told that the cancer in his right lung had spread to his hilar lymph nodes, lymph nodes near the area where the bronchi enter the lungs.


Sarkar, S., Jash, D., Maji, A., and P. Anupam. Approach to unequal hilum on chest X-ray. The Journal of Association of Chest Physicians. 2013. 1(2):32-37.

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