CorpusHuman Anatomy
RespiratoryRegion

Hilum and root of the lung

Hilum pulmonis; radix pulmonis

Also known as: lung root, pulmonary hilum, hilum, pulmonary ligament

The hilum is the wedge-shaped area on the mediastinal surface where the structures of the lung root — bronchus, pulmonary artery, pulmonary veins, bronchial vessels, nerves and lymphatics — enter and leave the lung.

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Overview

The root is the bundle of structures connecting the lung to the heart and trachea; the hilum is the area on the lung through which they pass. The root is enclosed in a sleeve of pleura where mediastinal parietal pleura reflects onto the lung as visceral pleura; below the root this sleeve hangs down as a loose double fold, the pulmonary ligament, which allows the root to move during breathing and the pulmonary veins to distend.

Contents: main (or lobar) bronchus, pulmonary artery, two pulmonary veins (superior and inferior), bronchial arteries and veins, the pulmonary nerve plexus and lymphatics with bronchopulmonary (hilar) nodes. Arrangement: right — the superior lobe (eparterial) bronchus lies highest and most posterior, the pulmonary artery is anterior to the bronchus, and the veins are anterior and inferior; left — the pulmonary artery is the most superior structure, the bronchus lies posterior and below it, and the veins are anterior and inferior. In both, the pulmonary veins are the most anterior and inferior structures.

Location

Middle of the mediastinal surface of each lung, opposite T5–T7.

Parts & subdivisions

  1. Bronchus
    Posterior; on the right the eparterial upper lobe bronchus is the highest structure.
  2. Pulmonary artery
    Anterior to the bronchus on the right; superior on the left.
  3. Pulmonary veins
    Superior and inferior; the most anterior and inferior structures on both sides.
  4. Pulmonary ligament
    Double layer of pleura hanging below the root.
  5. Bronchopulmonary nodes
    Hilar lymph nodes receiving lymph from the lung.

Anatomy

Relations

Right root: anteriorly the SVC, right phrenic nerve and right atrium; posteriorly the right vagus; superiorly the arch of the azygos vein. Left root: anteriorly the left phrenic nerve; superiorly the arch of the aorta; posteriorly the descending aorta and left vagus. The phrenic nerves pass in front of, and the vagi behind, the roots.

Function

  • Transmits airways, vessels, nerves and lymphatics between the lung and the mediastinum.
  • Anchors the lung to the mediastinum.

Clinical significance

Hilar lymphadenopathy

Bilateral symmetrical hilar lymphadenopathy suggests sarcoidosis; unilateral enlargement suggests lung cancer, TB or lymphoma. On a normal chest radiograph the left hilum lies higher than the right in most people, because the left pulmonary artery arches over the left main bronchus.

Pneumonectomy

Requires ligation of the pulmonary artery, the superior and inferior pulmonary veins and the main bronchus at the root, and division of the pulmonary ligament.

Mnemonics

RALS

Right: artery Anterior to the bronchus; Left: artery Superior to the bronchus. Phrenic in front, vagus behind.

Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.