Hilum of lung

The hilum of the lung (Pulmonary hilum) is the area on the medial surface of each lung where the major structures bronchi, pulmonary arteries, pulmonary veins, bronchial vessels, lymphatic channels, and nerves enter and exit the lung, connecting it to the mediastinum. The hilum serves as the "root" of the lung, acting as the gateway for all vascular, airway, lymphatic, and neural structures.

On XRay:

• On the right side, the hilar shadow is primarily formed by the ascending and descending pulmonary arteries and the right superior pulmonary vein. The right pulmonary artery bifurcates within the mediastinum before reaching the hilum.

• On the left side, the hilar density is produced by the left pulmonary artery (which arches over the left main bronchus), the left descending pulmonary artery, and the left superior pulmonary vein. The left pulmonary artery does not bifurcate until it reaches the hilum itself.

• The inferior pulmonary veins on both sides lie posterior to the lower hila and contribute only a small portion of the normal hilar density.