| category |
details |
| etymology |
- – derived from the Greek bronchos, meaning “windpipe.” – “mainstem” refers to its primary division from the trachea.
|
| aka and abbreviation |
– left main bronchus (LMB). – hyparterial bronchus. |
| definition |
- – the narrower, longer, and more oblique of the two primary bronchi. – originates at the carina and directs airflow to the left lung.
|
| principles |
- – structural classification: –
- a conducting airway facilitating airflow into the left lung. –
- diameter and length: –
- longer, narrower, and more oblique than the right main bronchus. –
- aspiration risk: – lower risk than the right main bronchus due to its angle and narrower lumen.
|
| parts |
- – proximal segment near the carina. –
- mid-segment before branching. –
- distal segment leading into secondary bronchi.
- branches: –
- left upper lobe bronchus. –
- left lower lobe bronchus.
|
| size |
|
| shape |
- – cylindrical.
- slightly tapering distally.
|
| position |
- arises from the carina at
- enters the left hilum of the lung. –
- courses more obliquely than the right main bronchus. –
- passes beneath the aortic arch and
- anterior to the esophagus. –
- relationship to the left pulmonary artery (PA):
- courses inferior to the left PA,
- distinguishing it as a hyparterial bronchus.
|
| character |
- – rigid but flexible: –
- maintains airway patency while allowing for movement.
|
| time |
- – develops during embryonic weeks 4–7
- . – branches from the laryngotracheal tube.
|
| blood supply |
- arteries: –
- left bronchial artery (arising from the thoracic aorta).
|
| venous drainage |
- – veins: –
- bronchial veins. – drains into the hemiazygos system.
|
| lymphatic drainage |
- – left hilar lymph nodes (station 10L). –
- left paratracheal lymph nodes
- station 4L). –
- subcarinal lymph nodes (station 7). – lower paratracheal nodes (station 3p).
|
| nerve supply |
– parasympathetic: – vagus nerve (CN X). – sympathetic: – sympathetic trunk. |
| embryology |
– arises as a primary division of the tracheobronchial tree. |
| histology |
- – epithelium: –
- pseudostratified ciliated columnar epithelium with goblet cells. –
- cartilage: – incomplete cartilaginous rings transitioning to plates distally. –
- muscular component: –
- contains smooth muscle fibers that regulate airway diameter.
|
| physiology & pathophysiology |
- – facilitates airflow to the left lung. – lower aspiration risk compared to the right due to its oblique course.
- muscular role in acute asthma: –
- bronchial smooth muscle contraction contributes to airway narrowing during asthma exacerbations. –
- pathophysiology: –
- obstruction from intrinsic or extrinsic compression
- inflammatory narrowing. –
- congenital anomalies affecting patency.
|
| diseases |
- – common: –
- left main bronchial stenosis. –
- extrinsic compression from aortic pathology.
- less common: –
- infection: – tuberculosis. –
- neoplasms: –
- malignant: – bronchogenic carcinoma
- benign: – bronchial hamartoma.
- mechanical disorders: –
- external compression from mediastinal masses or vascular anomalies.
|
| radiology |
- – CXR: – left main bronchus visible as an air column. – displacement may indicate mass effect or lung pathology. –
- CT: – preferred for evaluating bronchial patency and identifying external compression. –
- MRI: – limited role but useful in assessing soft tissue masses affecting the airway.
|
| key points & pearls |
- – longer and more oblique than the right main bronchus—
- affects aspiration risk and airway management.
- CXR assessment: – evaluate for deviation, extrinsic compression, or luminal narrowing. –
- CT is the gold standard for evaluating airway pathology. –
- muscular contraction in asthma: contributes to bronchoconstriction and airway narrowing.
|
