The hilum is located on the medial aspect of each lung and provides the only route via which other structures enter and exit the lung. The hilum also serves as the point of attachment for the lungroot and is the point at which the visceral and parietalpleura connect.
Location of the Hilum
The hilum is a large triangulardepression located superior to the centre of the lung’s mediastinalsurface and posterior to the cardiacimpression. Anteriorly, the hilum corresponds to the 4-5th costal cartilages and posteriorly to T5-T7.
The Root of the Lung
The root of the lung is located at the hilum of each lung, just above the middle of the mediastinal surface and behind the cardiac impression.
Structures that form the root of the lung enter and exit at the hilum, allowing the root to be connected to the heart and trachea.
The root of the lung is formed by:
a principal bronchus on one side
the eparterial and hyparterial bronchus on the other side
one pulmonary artery
two pulmonary veins
the bronchial arteries (one on one side and two on the other)
the bronchial veins
the pulmonary plexuses of nerves
bronchial lymph nodes
All of these structures are enclosed by a reflection of the pleura. The lung root also extends inferiorly as a narrow fold known as the pulmonary ligament.
The root of therightlung lies behind the superiorvenacava and part of the rightatrium (beneath the azygos vein).
The root of the leftlung passes beneath the aorticarch and infront of the descendingaorta.
The phrenicnerve, pericardiacophrenicartery and vein, and the anteriorpulmonaryplexus lie infront of each lung root. The vagusnerve and posteriorpulmonaryplexus lie behind.
Hilar Contents and Function
Pulmonary artery (right and left)
Transports deoxygenated blood from the right ventricle to the functional airways.
Pulmonary vein (superior and inferior)
Transports oxygenated blood to the left atrium.
Bronchus (right or left)
Bifurcation of the trachea – allows air to transit down the respiratory tree
Holds the lower part of the lungs in position. Opposite the 5-7th thoracic vertebral bodies.
Hilar appearance on chest x-ray
The hilar are visible on chest x-ray and are highlighted below. The v shape represents where the pulmonary artery from the lower lobe meets the pulmonary vein of the upper lobe – this is a key radiological landmark.
Hilar abnormalities can be unilateral or bilateral and are most often noted on chest x-rays and CT scans.
Bilateral hilar enlargement
Pulmonary arterial hypertension
Unilateral hilar enlargement
Metastatic malignancy (e.g. breast cancer)
Abnormal hilar position
Pneumonia – consolidation within a lung will often pull the hilar to the affected side (this can be seen on chest x-ray)
Pneumothorax – will often push the hilar away from the affected side (again this can be seen on chest x-ray)
1. Gray H, Vandyke Carter H. Gray’s anatomy 1858. Modified by Geeky Medics.
2. Mikael Häggström. Licence: CC0. Available from: [LINK]