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Left pulmonary artery

The left pulmonary artery (LPA) is the longer branch of the pulmonary trunk, carrying deoxygenated blood from the right ventricle to the left lung for gas exchange. It arises from the pulmonary trunk at the level of the sternal angle (T5–T6), passes horizontally to the left, arching over the left main bronchus, and enters the hilum of the left lung.

The LPA gives rise to lobar and segmental branches that follow the bronchial tree, ensuring perfusion of the upper and lower lobes of the left lung. It lies superior to the left main bronchus and pulmonary veins at the hilum, forming an important landmark in thoracic imaging and surgery.

Clinically, the LPA is evaluated in pulmonary embolism, pulmonary hypertension, congenital heart disease, vasculitis, and surgical planning for lung resections.

Synonyms

  • LPA

  • Arteria pulmonalis sinistra

  • Left branch of pulmonary artery

Function

  • Carries deoxygenated blood from the pulmonary trunk to the left lung

  • Delivers blood to the lobar and segmental pulmonary arteries, which perfuse lung tissue

  • Plays a vital role in gas exchange and cardiopulmonary circulation

  • Acts as a key anatomical landmark in thoracic surgery and radiology

Branches

  • Left upper lobar pulmonary arteries → to apicoposterior and anterior segments of upper lobe

  • Lingular branches → to superior and inferior lingula

  • Left lower lobar arteries → to superior and basal segments of lower lobe

MRI Appearance

T1-weighted images:

  • Flowing blood shows a signal void (black lumen)

  • Vessel wall appears hypointense, surrounded by hyperintense mediastinal fat

T2-weighted images (normal):

  • Lumen appears as a signal void due to continuous blood flow

  • Thrombosis may appear as intermediate-to-high signal filling defect

T2 TRUFISP (cardiac/respiratory-gated):

  • Depicts LPA as a bright, continuous vascular lumen with high contrast against adjacent lung and mediastinal structures

  • Useful for dynamic assessment of patency, stenosis, or compression

STIR (Short Tau Inversion Recovery):

  • Fat suppression improves vessel conspicuity in mediastinal fat

  • Perivascular edema or inflammation appears hyperintense

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • LPA lumen enhances brightly and homogeneously

  • Filling defects indicate embolism, thrombosis, or intraluminal tumor

  • Useful for MR angiography of pulmonary arteries

MRI Non-Contrast Cardiac-Gated 3D Imaging (Whole-heart):

  • Provides 3D visualization of the origin, course, and branching of the LPA

  • Clearly delineates its relationship to the pulmonary trunk, left main bronchus, and veins

  • Useful in patients with renal impairment or for preoperative mapping of congenital anomalies

CT Appearance

CT Coronary Angiography (CCTA) / Pulmonary Angiography (CTPA):

  • LPA opacifies brightly with contrast, clearly showing origin, length, and branching pattern

  • Axial and multiplanar views demonstrate its relationship with the bronchi and pulmonary veins at the hilum

  • Detects pulmonary embolism, stenosis, aneurysm, or external compression

  • 3D reconstructions provide surgical and interventional planning detail, especially in lung resections, transplant, and congenital heart disease

CT images

Left pulmonary artery anatomy CT coronal image -img-00000-00000

CT images

Left pulmonary artery anatomyct axial image -img-00000-00000

MRI images

Left pulmonary artery anatomy mri coronal image -img-00000-00000

MRI images

Left pulmonary artery mri image