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Hilum of lung

The hilum of the lung is a wedge-shaped region on the medial surface of each lung through which major bronchovascular and neural structures enter and leave the lung. It represents the point of attachment of the lung to the mediastinum and serves as the gateway for air, blood vessels, lymphatics, and nerves.

The hilum is a critical anatomical and radiological landmark, frequently assessed on chest radiographs and cross-sectional imaging for evaluation of pulmonary, vascular, and mediastinal conditions.

Synonyms

  • Pulmonary hilum

  • Lung hilum

Location

  • Situated on the medial surface of each lung

  • Faces the mediastinum

  • Opposite the cardiac impression

  • Approximately at the level of T5–T7 vertebrae

  • Connected to the mediastinum by the lung root

  • Inferior to the pulmonary artery arch and superior to the inferior pulmonary vein

Anatomical components

  • Main (primary) bronchus

  • Pulmonary artery

  • Superior and inferior pulmonary veins

  • Bronchial arteries and veins

  • Lymph nodes and lymphatic vessels

  • Pulmonary autonomic nerve plexus

Arrangement of structures (Root of lung)

Right lung hilum:

  • Bronchus: Posterior

  • Pulmonary artery: Anterior

  • Pulmonary veins: Inferior

Left lung hilum:

  • Pulmonary artery: Superior

  • Bronchus: Posterior

  • Pulmonary veins: Inferior

(Mnemonic: RALS – Right Anterior, Left Superior pulmonary artery)

Relations

Anteriorly:

  • Pericardium

  • Phrenic nerve and pericardiophrenic vessels

Posteriorly:

  • Vagus nerve

  • Esophagus (left more than right)

Superiorly:

  • Pulmonary artery

Inferiorly:

  • Pulmonary veins

  • Pulmonary ligament

Medially:

  • Mediastinum

Laterally:

  • Lung parenchyma

X-ray appearance

Chest radiograph (PA view):

  • Hila: Soft-tissue density shadows formed mainly by pulmonary arteries

  • Left hilum: Usually higher than the right

  • Normal contour: Concave or mildly convex lateral margins

  • Visibility: Bronchi not normally seen unless air-filled

CT appearance

CT lung window:

  • Bronchi: Air-filled, well-defined tubular structures

  • Pulmonary arteries and veins: Soft-tissue attenuation branching structures

  • Hilum outline: Clearly delineated against aerated lung

  • Lymph nodes: Normally small and inconspicuous

  • Excellent for evaluating bronchovascular relationships

MRI appearance

T1-weighted images:

  • Pulmonary vessels: Intermediate signal with flow voids

  • Bronchi: Low-signal walls with central signal void from air

  • Fat planes: High signal aiding structural differentiation

T2-weighted images:

  • Pulmonary vessels: Flow-related signal voids or intermediate signal

  • Bronchi: Low-signal walls with high-signal surrounding lung parenchyma

  • Lymphatic tissue: Intermediate signal

STIR:

  • Fat suppression: Improves contrast between hilum structures and surrounding fat

  • Bronchovascular structures: Intermediate-to-low signal

CT image

Hilum of lung CT Anatomy, Location and Imaging Appearance CT anatomy image -img-00000-00000

X-Ray image

Hilum of lung X RAY Anatomy, Location and Imaging Appearance CT anatomy image -img-00000-00000