Applied Anatomy of Bronchopulmonary Segments
Foreign Body Aspiration
Why right side is more common:
- Right principal bronchus is shorter, wider, and more vertical (25° from trachea vs 45° on left)
- More directly in line with the trachea
- Aspirated material therefore preferentially enters the right bronchial tree
Site of lodgement by position:
| Position | Site of Lodgement |
|---|---|
| Erect/sitting | Right lower lobe — posterior basal segment (S10) |
| Supine | Superior (apical) segment of right lower lobe (S6) — most dependent posteriorly |
| Left lateral decubitus | Right-sided segments — secretions flow toward carina, stimulating cough |
In children: Foreign bodies often lodge at the carina or in the right main bronchus.
Aspiration Pneumonia
- Aspirated material in the supine position enters the superior (apical) segment of the lower lobe, right > left
- Most dependent bronchopulmonary segment in the supine position: S6 (superior/apical of lower lobe)
- This segment is therefore the most common site of aspiration pneumonia and aspiration lung abscess in bedridden patients
Segmental Resection
Basis: Each bronchopulmonary segment is an independent anatomical, functional, and surgical unit with its own bronchus, artery, lymphatics, and autonomic supply.
Indication: Localised chronic disease confined to one or more segments — tuberculosis, bronchiectasis, benign neoplasm.
Technique:
- The surgeon works along the intersegmental veins to identify the planes between segments
- Intersegmental veins must not be ligated — they drain adjacent healthy segments
- Only the diseased segment is removed; surrounding healthy lung tissue is preserved
Most common indication: Bronchiectasis (most often affecting basal segments of lower lobes).
Bronchoscopy
- Passage of a bronchoscope through the mouth, larynx, and trachea into the bronchial tree
- Allows direct visualisation of the interior of the bronchi down to the level of segmental bronchi
- Carina is visible at bifurcation — widening suggests subcarinal lymph node enlargement (malignancy, TB, sarcoidosis)
- Foreign bodies can be retrieved; biopsies taken; secretions aspirated
Bronchiectasis
- Permanent pathological dilatation of bronchi and bronchioles due to chronic necrotising infection
- Bronchi become filled with pus → airway obstruction → foul-smelling sputum
- Most commonly affects: Basal segments of the lower lobes (most dependent in erect posture)
- Postural drainage is a cornerstone of management
Tuberculosis and Segment Distribution
- Primary TB: May affect any segment; commonly lower lobes and middle lobe (well-ventilated)
- Reactivation (post-primary) TB: Characteristically affects apical and posterior segments of the upper lobes (S1, S2) — high oxygen tension favours Mycobacterium tuberculosis
- Disease may spread from one segment to another in TB and bronchogenic carcinoma
Pneumonia — Surface Anatomy for Auscultation
| Lobe | Auscultation Region |
|---|---|
| Upper lobe (both sides) | Above 4th rib, anteriorly and posteriorly |
| Middle lobe (right) / Lingula (left) | Between 4th and 6th ribs, anteriorly on right; anteriorly on left |
| Lower lobes (both sides) | Best heard posteriorly (lower chest) |
Carina — Clinical Significance
- Normal carina angle: < 70°
- Widened carina on chest X-ray or bronchoscopy: suggests subcarinal lymph node enlargement — causes include lung carcinoma (especially left hilar), lymphoma, tuberculosis, sarcoidosis
- Carina is highly sensitive — stimulation triggers the cough reflex
- Used as a landmark during bronchoscopy and endotracheal intubation
Paradoxical Respiration
Occurs with a flail chest (multiple rib fractures — two or more adjacent ribs fractured in two or more places):
- Inspiration: The flail segment is sucked inward (paradoxically) as surrounding chest wall rises
- Expiration: The flail segment moves outward as surrounding chest wall falls
- Results in ineffective ventilation and may be life-threatening