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Right posterior segmental bronchus (B2, B2a, B2b)

The right posterior segmental bronchus (B2) is one of the three segmental bronchi of the right superior lobar bronchus, alongside the apical (B1) and anterior (B3) branches. It arises from the posterior aspect of the superior lobar bronchus and courses posteriorly and slightly laterally, supplying the posterior segment of the right upper lobe. B2 commonly divides into two subsegmental branches: B2a (superior branch) and B2b (inferior branch), which distribute air to the posterior apical parenchyma. It plays an important role in bronchoscopy, CT evaluation, and surgical planning, particularly in segmentectomy or lobectomy.

Synonyms

  • B2 bronchus

  • Right posterior bronchus

  • Posterior segmental bronchus of right upper lobe

Function

  • Provides air conduction to the posterior segment of the right upper lobe

  • Facilitates gas exchange in the superior-posterior lung parenchyma

  • Plays a role in mucus clearance from posterior lung regions

  • Serves as a key landmark in bronchoscopy, HRCT, and thoracic surgery

CT Appearance

Lung Window:

  • B2 appears as an air-filled hypodense (black) tubular structure running posteriorly from the right superior lobar bronchus

  • B2a and B2b branches extend into the posterior segment of the right upper lobe

  • Normal bronchial walls are thin; disease may cause wall thickening, luminal narrowing, or obstruction

  • Tree-in-bud nodularity may indicate infection in the posterior segment

Mediastinal Window:

  • Bronchial wall visualized as a thin soft tissue rim

  • Helps differentiate endobronchial lesions from peribronchial lymphadenopathy or extrinsic compression

Contrast-enhanced CT (CECT):

  • Enhances bronchial wall and surrounding mediastinal vessels

  • Useful for assessing endobronchial tumors, carcinoma spread, or external vascular compression

  • HRCT delineates subsegmental divisions (B2a, B2b) and bronchial patency

MRI Appearance

T1-weighted images:

  • Air within B2 lumen appears as a signal void (black)

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

T2-weighted images:

  • Air-filled lumen remains a signal void

  • If fluid, pus, or mucus is present, the lumen becomes bright hyperintense

  • Bronchial wall thickening (infection, tumor, or inflammation) appears intermediate to hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal wall shows thin, mild homogeneous enhancement

  • Pathological changes show irregular, asymmetric wall enhancement or nodular masses within the bronchus or along the wall

CT images

Right posterior segmental bronchus (B2, B2a, B2b) anatomy CT coronal image -img-00000-00000

CT images

Right posterior segmental bronchus (B2, B2a, B2b) anatomy CT coronal image -img-00000-00000_00001