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Right middle lobar bronchus

The right middle lobar bronchus is a secondary bronchus of the right lung, arising from the intermediate bronchus (continuation of the right main bronchus after the right upper lobar bronchus branches off). It courses laterally and anteriorly, passing below the right upper lobar bronchus and above the right lower lobar bronchus, to enter the right middle lobe.

The bronchus typically bifurcates into two segmental bronchi: the lateral segmental bronchus (B4) and the medial segmental bronchus (B5), which supply the corresponding lung segments.

This airway is clinically important in bronchoscopy, segmentectomy, and imaging. Pathologies affecting it include bronchiectasis, airway stenosis, obstruction by tumor, and infections confined to the right middle lobe.

Synonyms

  • Bronchus lobaris medius dexter

  • Middle lobe bronchus (right)

  • Secondary bronchus of right middle lobe

Function

  • Conducts air from the intermediate bronchus into the right middle lobe

  • Splits into B4 and B5 to ventilate the lateral and medial segments

  • Plays a role in ventilation-perfusion balance of the middle lobe

  • Serves as a bronchoscopic and surgical landmark in lobectomies and segmentectomies

Branches

  • Lateral segmental bronchus (B4) → supplies lateral segment of middle lobe

  • Medial segmental bronchus (B5) → supplies medial segment of middle lobe

MRI Appearance

T1-weighted images:

  • Air-filled bronchial lumen appears as a signal void (black)

  • Bronchial wall appears hypointense, outlined by peribronchial fat and vessels

T2-weighted images (normal):

  • Lumen remains a dark signal void

  • Surrounding peribronchial tissues show intermediate signal; mucus plugs or fluid-filled bronchus appear hyperintense

T2 TRUFISP (respiratory-gated):

  • Demonstrates the right middle lobar bronchus as a sharply defined airway with bright contrast between lumen and adjacent lung parenchyma

  • Cine-like acquisition provides functional assessment of airway motion and narrowing

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, improving detection of peribronchial edema, inflammation, or tumor infiltration

  • Lumen remains dark

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Bronchial wall may enhance if inflamed, infiltrated, or vascularized by tumor

  • Peribronchial lesions become clearly visible

MRI Non-Contrast 3D Cardiac/Respiratory-Gated Imaging:

  • Provides 3D depiction of bronchial tree, clearly showing intermediate bronchus → middle lobar bronchus → segmental branches (B4, B5)

  • Useful for virtual bronchoscopy, surgical mapping, and congenital anomaly detection

CT Appearance

CT Chest (non-contrast):

  • Right middle lobar bronchus visualized as an air-filled tubular structure branching from the intermediate bronchus

  • Bronchial wall thickening, mucus plugging, or obstruction can be detected

  • Best for diagnosing bronchiectasis, airway stenosis, or foreign body

CT Coronary Angiography (CCTA) / CT Pulmonary Angiography (for correlation):

  • Although focused on vessels, reconstructed datasets also show bronchial anatomy

  • Multiplanar and 3D reconstructions allow precise visualization of B4 and B5 branches and their relation to pulmonary arteries/veins

  • Critical for surgical planning (lobectomy, segmentectomy) and correlation with pulmonary venous anatomy

CT image

Right middle lobar bronchus CT IMAGE

MRI image

Right middle lobar bronchus anatomy MRI coronal image -img-00000-00000