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Left lung (inferior lobe)

The inferior lobe of the left lung is the larger and more posteriorly located lobe of the left lung. It is separated from the superior lobe by the oblique fissure. The inferior lobe extends from the hilum and posterior chest wall down to the diaphragm, forming the basal portion of the lung. It is composed of five bronchopulmonary segments:

  • Superior (apical) segment (S6)

  • Anteromedial basal segment (S7+8)

  • Lateral basal segment (S9)

  • Posterior basal segment (S10)

This lobe is ventilated by the left inferior lobar (secondary) bronchus, which branches into segmental bronchi supplying the above segments. The inferior lobe plays a crucial role in gas exchange, particularly in the posterior lung fields that are most active during deep inspiration.

Synonyms

  • Left lower lobe

  • Inferior lobe of left lung

  • Left pulmonary lower lobe

Function

  • Provides ventilation and gas exchange for the posterior and basal portions of the left lung

  • Participates in oxygen uptake and carbon dioxide elimination

  • Supports mucus clearance through segmental bronchial drainage

  • Plays a key role in postural changes in ventilation-perfusion (V/Q) matching, especially in upright and supine positions

CT Appearance

Lung Window:

  • Inferior lobe parenchyma appears as a homogeneous, aerated (hypodense, black) region, separated from the superior lobe by the oblique fissure

  • Pulmonary vessels and bronchi are clearly outlined against aerated lung tissue

  • Pathology: consolidation (pneumonia), ground-glass opacities, atelectasis, fibrosis, and nodules appear as increased density (gray/white) within the lobe

Mediastinal Window:

  • Allows assessment of fissures, hilum, mediastinal relation, and adjacent pleura/diaphragm

  • Consolidation or mass lesions appear as soft tissue densities

  • Useful for differentiating pleural effusion, diaphragmatic invasion, or lymphadenopathy adjacent to the inferior lobe

Contrast-enhanced CT (CECT):

  • Enhances pulmonary vessels and mediastinal relations

  • Excellent for evaluating pulmonary embolism, tumor vascularity, or segmental anatomy before surgery

  • HRCT provides detailed view of airways, interlobular septa, and early interstitial disease

MRI Appearance

T1-weighted images:

  • Aerated lung parenchyma appears as a signal void (black)

  • Bronchovascular structures appear as low signal intensity lines

  • Pathology such as consolidation or tumor appears as intermediate to low signal

T2-weighted images:

  • Aerated lung remains a signal void

  • Fluid, edema, or inflammation (e.g., pneumonia, effusion, tumor infiltration) appear bright hyperintense

  • Useful for distinguishing solid vs. fluid-based lesions in the lobe

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal lung parenchyma does not enhance

  • Masses, inflammatory lesions, or vascular structures enhance variably depending on pathology

  • Helpful for tumor characterization, pleural involvement, and vascular invasion

CT image

Left lung (inferior lobe) anatomy CT coronal image -img-00000-00000