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Right lung (middle lobe)

The middle lobe of the right lung is the smallest lobe of the right lung, situated between the horizontal fissure (superiorly) and the oblique fissure (inferiorly). It is wedge-shaped and lies adjacent to the anterior chest wall, extending from the midclavicular line to the hilum. The middle lobe is ventilated by the middle lobar bronchus, which divides into two segmental bronchi: the medial segmental bronchus (B5) and the lateral segmental bronchus (B4). Venous drainage is via the middle lobe vein, a tributary of the right superior pulmonary vein. This lobe is a frequent site of infection and collapse due to its narrow bronchial entry and dependent position.

Synonyms

  • Lobus medius pulmonis dextri

  • Right pulmonary middle lobe

  • Middle lobe of right lung

Function

  • Contributes to ventilation and gas exchange within the right lung

  • Functions in oxygen uptake and carbon dioxide elimination

  • Works with other lobes to maintain pulmonary reserve and lung mechanics

  • Clinically important in conditions such as middle lobe syndrome, infections, and segmentectomy planning

CT Appearance

Lung Window:

  • Middle lobe appears as a well-aerated region bordered superiorly by the horizontal fissure and inferiorly by the oblique fissure

  • Normal parenchyma is uniformly low attenuation (black)

  • Pathology: atelectasis shows wedge-shaped opacity, infections appear as consolidation or ground-glass opacity, tumors as soft tissue nodules or masses

Mediastinal Window:

  • Outlines the bronchovascular structures of the middle lobe

  • Useful for assessing hilar extension, masses, and mediastinal lymphadenopathy

  • Demonstrates the middle lobe vein draining into the right superior pulmonary vein

Contrast-enhanced CT (CECT):

  • Enhances pulmonary vessels, better delineating bronchovascular anatomy

  • Helpful for detecting vascular invasion, tumors, pulmonary emboli, and middle lobe collapse

  • HRCT provides fine detail for interstitial disease and recurrent infections

MRI Appearance

T1-weighted images:

  • Aerated middle lobe appears as a signal void (black)

  • Lung parenchyma is not well visualized on standard T1, but mediastinal structures and vessels are clearly defined

T2-weighted images:

  • Normal aerated lung remains signal void

  • Fluid, infection, or consolidation in the middle lobe appears bright hyperintense, improving detection of pathology

  • Edematous or collapsed regions are also hyperintense compared to normal aerated lung

T1 Post-Contrast (Gadolinium-enhanced):

  • Middle lobe vessels and inflamed or neoplastic tissue show strong enhancement

  • Consolidation, tumors, or vascular lesions can be delineated from adjacent normal parenchyma

CT image

Right lung (middle lobe) anatomy CT coronal image -img-00000-00000