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Inferior lingular bronchus of left lung (B5)

The inferior lingular bronchus (B5) is one of the two segmental bronchi of the lingula of the left upper lobe, the other being the superior lingular bronchus (B4). The lingula is the left lung counterpart of the right middle lobe, and B5 supplies the inferior lingular segment, located anterior and inferior within the lingula. It arises from the lingular division bronchus (a branch of the left upper lobe bronchus) and courses downward and forward. Clinically, the B5 bronchus is important because the lingula is a frequent site for pneumonia, bronchiectasis, and atelectasis.

Synonyms

  • B5 bronchus

  • Inferior lingular segmental bronchus

  • Lingular segmental bronchus (inferior)

Function

  • Provides air supply to the inferior lingular segment of the left upper lobe

  • Ensures ventilation and gas exchange in the anteroinferior portion of the lingula

  • Facilitates mucus clearance from the inferior lingular segment

  • Acts as an important landmark for bronchoscopy and thoracic surgery (lingulectomy, segmentectomy)

CT Appearance

Lung Window:

  • B5 appears as an air-filled tubular branch arising from the lingular division bronchus and coursing anterior-inferiorly toward the lingula

  • Normally, the lumen is hypodense (black) with thin, barely perceptible walls

  • Pathology: wall thickening (bronchitis), mucus plugging, bronchiectasis (dilated lumen), or consolidation in its drainage territory

Mediastinal Window:

  • Shows B5 as a thin soft-tissue rimmed airway with surrounding vascular structures

  • Useful for evaluating endobronchial lesions, peribronchial lymph nodes, or extrinsic compression

  • Provides complementary detail for surgical or interventional planning

Contrast-enhanced CT (CECT):

  • Enhances bronchial wall and adjacent pulmonary vessels

  • Highlights bronchial stenosis, tumors, extrinsic compression, or peribronchial spread of carcinoma

  • HRCT offers detailed evaluation of airway caliber, wall thickness, and lung parenchyma in the lingula

MRI Appearance

T1-weighted images:

  • Air in the lumen appears as a signal void (black)

  • Bronchial wall appears low signal, surrounded by intermediate signal lung tissue and peribronchial fat

T2-weighted images:

  • Normal air-filled lumen remains a signal void

  • Fluid or mucus within B5 appears bright hyperintense

  • Inflamed or thickened bronchial wall shows intermediate to hyperintense signal

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal bronchial wall enhances minimally and evenly

  • Pathology (infection, tumor, granuloma) shows irregular or nodular enhancement, with possible luminal obstruction

CT images

Inferior lingular bronchus of left lung (B5) anatomy CT coronal image -img-00000-00000

CT images

Inferior lingular bronchus of left lung (B5) anatomy CT coronal image -img-00000-00000_00001