The hilum (pl. = hila) is a structure or area found on the medial aspect of each lung. This area of the lung, which is sometimes also referred to as the hilus, is somewhat triangular in shape and is the area where the bronchi and neurovascular structures of the lungs enter and exit the lungs.
In addition to a hilum, each lung also has a lung root that is enclosed by a layer of pleura. The root of each lung is comprised of; the bronchus, pulmonary artery and vein, bronchial arteries and veins, pulmonary plexuses of nerves, areolar tissue, lymphatic vessels and bronchial lymph glands.
The pulmonary ligament, which is a narrow fold, is an inferior extension of the root of the lung. Note that the structures that make up the root of the lung enter and exit the lungs at the hilum.
The hilum of the lung is the only area of the lung where structures associated with the lungs can enter or exit the lungs.
Abnormalities of the hilum can present either as unilateral or bilateral abnormalities. These abnormalities can be detected on a chest X-ray and can present as either changes in the position, the size and/or the density of the hilar region. Such abnormalities or changes are commonly seen to come about as a result of various types of lung cancer.
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