The lung hila or roots are found on the medial aspect of each lung and transmit structures such as vessels and bronchi between the lung and mediastinum. The left and right lung roots are similar but not identical. The roots of the lung lie between T5 to T7 vertebrae ⁵.

The hilar point is a point where the upper lobe vein crosses over the pulmonary artery. The hilar angle is the angle between the vessels at the hilar point, which usually measures 120° ⁵.

The term hilum is singular while hila is plural. The term hilar is an adjective ⁶.

Gross anatomy

The structures of the lung hilum are enclosed in a sleeve of pleura continuous below with the pulmonary ligament ⁵. Each hilum contains the following:

• a main bronchus that divides based on the lobar anatomy

• a pulmonary artery

• superior and inferior pulmonary veins

• lymph nodes and lymphatic channels

• bronchial arteries and veins

• autonomic nerves

Left hilum

The left hilum lies below the aortic arch and anterior to the descending aorta. The left main bronchus lies at the most posterior aspect of the hilum, with the left superior pulmonary vein located anteriorly and the left inferior pulmonary vein occupying the inferior portion of the hilum. The left pulmonary artery is anterosuperior to the left main bronchus. Pulmonary veins always lie anteroinferior to the pulmonary artery ⁵.

Right hilum

The right hilum lies below the arch of the azygos vein, posterior to the superior vena cava and right atrium. Right pulmonary veins are located at the anterior part of the hilum, followed by right pulmonary arteries, and lobar bronchi ⁵.

Radiographic features

A hilum appears as a composite opacity in a radiograph or a CT scan at the root of the lung produced by various structures overlapping each other such as vessels, bronchi, nerves, lymph nodes and other tissues ⁶.