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Medial segmental bronchus of right lung (B5)

The medial segmental bronchus (B5) is one of the two segmental bronchi of the right middle lobar bronchus, the other being the lateral segmental bronchus (B4). It arises from the middle lobar bronchus and courses medially and anteriorly to supply the medial segment of the right middle lobe. The medial segment corresponds anatomically to the cardiac impression of the right lung, where the bronchus lies in close relation to the right atrium and pericardium. B5 is an important bronchus in bronchoscopy, radiological evaluation, and middle lobectomy surgeries.

Synonyms

  • B5 bronchus

  • Right medial bronchus

  • Medial segmental bronchus of middle lobe

Function

  • Conducts air to the medial segment of the right middle lobe

  • Maintains ventilation and gas exchange in the cardiac impression region of the right lung

  • Plays a role in mucus clearance from the medial segment

  • Serves as a radiological and surgical landmark in thoracic imaging and lung resection procedures

CT Appearance

Lung Window:

  • B5 appears as a tubular, air-filled hypodense (black) structure branching medially from the right middle lobar bronchus

  • Normally thin-walled and patent

  • Pathological findings: wall thickening (bronchitis), obstruction (mucus, tumor), or air-trapping and atelectasis in the medial segment

Mediastinal Window:

  • Shows B5 as a thin soft tissue–rimmed structure coursing medially toward the hilum

  • Useful for evaluating endobronchial tumors, peribronchial lymph nodes, or external vascular compression

  • Demonstrates close relation of B5 to the right atrium and pericardium

Contrast-enhanced CT (CECT):

  • Enhances bronchial wall and adjacent mediastinal vessels

  • Excellent for identifying bronchial stenosis, endobronchial lesions, and mediastinal invasion by tumors

  • HRCT provides fine detail of lumen caliber, wall thickness, and branching pattern

MRI Appearance

T1-weighted images:

  • Air within the B5 lumen shows as a signal void (black)

  • Bronchial wall appears low signal intensity, surrounded by hyperintense mediastinal fat

T2-weighted images:

  • Lumen remains a signal void if air-filled

  • Fluid, secretions, or mucus retention in B5 appear bright hyperintense

  • Thickened or inflamed bronchial walls show intermediate-to-high signal intensity

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall shows thin, mild rim enhancement

  • Pathological findings (infection, granulomatous disease, tumor infiltration) appear as irregular, thickened, and heterogeneously enhancing bronchial walls or masses

CT images

Medial segmental bronchus of right lung (B5) anatomy CT coronal image -img-00000-00000

CT images

Medial segmental bronchus of right lung (B5) anatomy CT coronal image -img-00000-00000_00001