Anatomy for bronchoscopy

Anatomy for bronchoscopy and airway management

Overview

Airway anatomy is highly relevant to diagnosis and management in critical care.

• this includes both the upper airway (e.g. laryngoscopy, threats to airway patency and protection) and the lower airway (e.g. bronchoscopy and respiratory pathology)
• bronchoscopic anatomy follows the airway from the vocal cords to the segmental bronchi.

The bronchoscopist navigates from within the airway using a series of landmarks to maintain orientation, localise pathology and safely perform procedures. 

• You don’t need to know anatomy, you need to be able to find it!
• Safe bronchoscopy depends on three skills:
  • maintaining orientation
  • recognising normal anatomy and common variants
  • identifying abnormalities

Many apparent abnormalities are simply normal variants. Equally, important disease is often identified because the airway has an abnormal appearance.

Bronchoscopy Roadmap

Most bronchoscopic examinations follow the same sequence:

• Upper airway (unless intubated)
• Vocal cords (unless intubated)
• Trachea
• Carina
• Right main bronchus
• Right upper lobe
• Bronchus intermedius
• Right middle lobe
• Right lower lobe
• Left main bronchus
• Left upper lobe
• Lingula
• Left lower lobe

If orientation is lost, return to the carina and restart from there.

Bronchoscopic Orientation

Know how to maintain orientation is vital – if in doubt always come back to the carina:

• The carina is your compass
• The trachea is D-shaped, cartilage is anterior, and membrane is posterior

Use the following landmarks continuously:

• posterior membrane (has characteristic “racing stripes” from the longitudinal striations of the trachealis muscle)
• main carina
• secondary carinae
• major airway branches

Remember:

• upper lobes branch superiorly
• lower lobes branch inferiorly
• the right bronchial tree is more vertical (almost continuous with the trachea)
• the left bronchial tree is more horizontal

Upper Airway

The upper airway and larynx are functionally important for:

• Respiration
• Humidification 
• airway protection
• Phonation, and 
• procedural access in critical care

A useful navigation sequence is:

• Uvula → Epiglottis → Larynx
• particularly useful when secretions, blood or distorted anatomy obscure normal landmarks.

The laryngeal inlet is the opening from the pharynx into the larynx. It is bounded by:

• Epiglottis (anterior)
• Arytenoids + interarytenoid notch (posterior)
• Aryepiglottic folds (lateral)

Vallecula, hyoepiglottic ligament, and glottic exposure

• The epiglottis is the “gateway to the larynx” during laryngoscopy
• The epiglottis is connected to the hyoid by the hyoepiglottic ligament
  • Seating the tip of the laryngoscope blade in the vallecula (anterior to the epiglottis) activates (stretches) the hyoepiglottic ligament and causes the epiglottis to lift anteriorly exposing the glottis
  • Failure to do this correctly is a common reason for poor laryngoscopic view

The vocal cords sit below the laryngeal inlet. They form the glottis and divide the upper airway from the lower airway. Unless paralysed, they provide a dynamic sphincter that the bronchoscopy must negotiate.

The cricoid cartilage forms the boundary between larynx and trachea.

• lies immediately below the vocal cords and above the first tracheal ring
• It is the only complete cartilaginous ring in the airway
• It is shaped like a signet ring resulting in a broad cartilagenous wall posteriorly
• This makes it an important landmark during:
  • Front of neck access (cricothyroidotomy and tracheostomy)
  • airway stenosis assessment
  • interventional airway procedures
• The cricothyroid membrane lies anteriorly, between the cricoid cartilage and the thyroid cartilage

Common upper airway normal variants include:

• omega-shaped epiglottis (may be more common in obesity)
• prominent arytenoids
• variation in glottic size

Upper airway landmarks are not visible when bronchoscopy is performed in a patient who is already intubated. Only the features of the endotracheal tube (ETT) will be visible as the bronchoscope pass along it:

• Clear plastic cylindrical tube lumen
• external depth markings on ETT may be visible
• Murphy’s eye near distal tip of ETT

Trachea

The trachea extends from the cricoid cartilage to the carina.

• Healthy trachea shows C‑shaped anterior cartilaginous rings with a membranous posterior wall.
• The adult trachea contains approximately 18–22 cartilaginous rings.
• Usually 9-15cm in length in adults

For bronchoscopy, only a few features truly matter:

• cartilage anteriorly
• membrane posteriorly
• slight rightward deviation approaching the carina
• dynamic movement during breathing and coughing

Important adjacent structures (especially relevant for FONA procedures)

• Anterior
  • Great vessels
    • Brachiocephalic (innominate) artery – crosses anterior to the upper thoracic trachea
    • Brachiocephalic (innominate) vein – passes anterior to the trachea in the superior mediastinum
    • Distally
      • Aortic arch – lies anterior and to the left of the distal trachea
      • Superior vena cava (SVC) – lies anterolateral to the right side of the trachea
      • Pulmonary trunk – lies anterior to the distal trachea and carina
  • Thyroid and vessels
    • Thyroid isthmus crosses the anterior surface of the trachea at the level of the 2nd–4th tracheal rings
    • The inferior thyroid veins descend anterior to the upper trachea and drain into the brachiocephalic veins.
    • The thyroid ima artery (when present; anatomical variant) ascends on the anterior trachea, usually arising from the brachiocephalic trunk or aortic arch.
• Lateral
  • Recurrent laryngeal nerves run bilaterally along the trachea
  • Branches of the inferior thyroid arteries run posterolateral to the trachea near the recurrent laryngeal nerves.
  • The thyroid lobes lie on either side of the upper trachea and extend posteriorly towards the oesophagus and carotid sheath
• Posterior
  • Esophagus

These adjacent structures can distort the airway through:

• Masses (e.g. goitre, tumours)
• lymphadenopathy
• fibrosis
• previous surgery
• Vessel enlargement (e.g. aneurysm, SVC obstruction)

Mild dynamic movement of the posterior membrane during expiration is normal

• Trachealis muscle contracts and constricts trachea during coughing
• Excessive expiratory collapse of the airway is abnormal and may indicate:
  • Tracheobronchomalacia – weakness of the cartilaginous airway wall.
  • Excessive Dynamic Airway Collapse (EDAC) – exaggerated inward bulging of the posterior membranous wall.

A tracheal bronchus (“pig bronchus”) is an anatomical variant that arises directly from the trachea above the carina and usually supplies part of the right upper lobe.

• Occurs in 0.1-2% of people, usually discovered incidentally
• Recognition is important because it may affect:

• endotracheal tube positioning
• lung isolation and one-lung ventilation
• bronchoscopic navigation and interpretation

Carina

The carina is the most important landmark in bronchoscopy.

• It is the bifurcation between the right and left main bronchi
• Experienced bronchoscopists continually return to the carina to maintain orientation.

At the carina:

• the right main bronchus is shorter, wider and more vertical
• the left main bronchus is longer, narrower and more horizontal
• the posterior membranous wall identifies posterior orientation
• the cartilaginous wall identifies anterior orientation

The carina lies within the middle mediastinum and is surrounded by structures commonly encountered during bronchoscopy, EBUS and transbronchial needle aspiration. Important relationships include:

• Anterior: pulmonary trunk and origin of the right and left pulmonary arteries
• Posterior: oesophagus and descending thoracic aorta
• Inferior: left atrium (which is below subcarinal space (station 7), one of the most frequently sampled lymph node stations during bronchoscopy)
• Right: azygos vein arch and right paratracheal lymph node stations
• Left: aortic arch, aortopulmonary window, and left paratracheal lymph node stations

Unexpected carinal appearances are “red flags” for underlying pathology:

Finding	Possible Cause
Widened carinal angle	Subcarinal lymphadenopathy or other disease outside the airway rather than within it
Blunted carina	Malignancy
Distorted anatomy	Mediastinal mass
Fixed carina	Infiltrative disease
Shifted carina	Volume loss or mediastinal displacement

Mediastinal and Hilar Relations

Lymph Node Stations

• These are less relevant in the ED and ICU setting, but are important in diagnostic bronchoscopy as EBUS and TBNA targets.
• The most important targets are:

Station	Location
4R	Right lower paratracheal
4L	Left lower paratracheal
7	Subcarinal
10R	Right hilar
10L	Left hilar
11R	Right interlobar
11L	Left interlobar

Vascular relations – important structures to miss when performing biopsies!

• Azygos Vein
  • The azygos vein arches over the right main bronchus before entering the superior vena cava.
  • It creates an important landmark for:
    • station 4R
    • right paratracheal anatomy
    • upper mediastinal orientation
• Aortopulmonary Window
  • Located between aortic arch and left pulmonary artery
  • It contains stations 5 and 6 and is an important radiological landmark when correlating CT findings with airway anatomy.
• Pulmonary arteries
  • The left pulmonary artery passes superior to the left main bronchus.
  • The right pulmonary artery lies anterior to the right main bronchus.
  • These relationships are useful for understanding hilar pathology, EBUS anatomy, and mediastinal staging.

Bronchoscopic Nomenclature

Segmental bronchi are designated using the letter B followed by a number.

Segment	Right Lung	Left Lung
B1	Apical (RUL)	Apical (LUL upper division)
B2	Posterior (RUL)	Posterior (LUL upper division)
B3	Anterior (RUL)	Anterior (LUL upper division)
B4	Lateral (RML)	Superior lingular
B5	Medial (RML)	Inferior lingular
B6	Superior segment (RLL)	Superior segment (LLL)
B7	Medial basal	Medial basal (often absent on the left)
B8	Anterior basal	Anterior basal
B9	Lateral basal	Lateral basal
B10	Posterior basal	Posterior basal

Important differences to note in the left lung:

• Left medial basal (B7) is usually absent
• Left apical and posterior (B1 and B2) are often fused (B12 or apicoposterior) or arise from common bronchial trunk. 

Right Bronchial Tree

The right bronchial tree is shorter, wider, and more vertical than the left. These characteristics contribute to the ease of:

• right mainstem intubation
• right-sided aspiration
• preferential entry of bronchoscopes into the right lung

Right Main Bronchus

• Approximately 2 cm long.
• Rapidly divides into:

• right upper lobe bronchus
  • Usually trifurcates into:
    • B1 apical
    • B2 posterior
    • B3 anterior
  • This is the first major branch seen on entering the right lung with a bronchoscopy (unless there is a tracheal (“pig”) bronchus.
• bronchus intermedius
  • extends from the RUL take-off to the middle lobe bronchus.
  • This is an important orientation pointsin bronchoscopy.
    • The anterior wall becomes the middle lobe
    • The posterior wall becomes the lower lobe
  • Important relationships:
    • RML originates anteriorly
    • RLL continues posteriorly
    • B6 (superior segment) arises posteriorly
• Secondary carinae:
  • RC1 = RUL–BI carina
  • RC2 = RML–RLL carina

Right Middle Lobe

• Typically divides into:
  • B4 lateral
  • B5 medial

Right Lower Lobe

• The superior segment (B6) arises posteriorly.
  • It is a useful landmarks for re-establishing lower-lobe orientation
• The basal trunk typically divides into:
  • B7 medial basal
  • B8 anterior basal
  • B9 lateral basal
  • B10 posterior basal

Left Bronchial Tree

The left bronchial tree, compared to the right, is longer, narrower, and more horizontal

• Rotate the scope approximately 90° left so the anterior wall lies at around the 3 o’clock position to enter the left upper lobe.

Left Upper Lobe

• Upper Division 

• B1 apical
• B2 posterior
• B3 anterior
• However, while textbooks depict separate B1 (apical), B2 (posterior) and B3 (anterior) segments, fusion of B1 and B2 into a common apicoposterior trunk is common
• Lingula
  • The lingula is the left-sided equivalent of the middle lobe.
  • It divides into:

• B4 superior lingular
• B5 inferior lingular
• Secondary carinae:
  • LC1 = upper division–lingula
  • LC2 = lingula–LLL

Left Lower Lobe

• Divides into:
  • B6 superior segment
  • basal trunk
• The basal trunk typically gives rise to:

• B8 anterior basal
• B9 lateral basal
• B10 posterior basal
• B7 (medial) is usually absent.

Practical tips and pitfalls

Common ICU Bronchoscopy Targets

• Most ICU bronchoscopies involve localisation of secretions, aspiration, bleeding, or airway pathology. Knowing the common sites helps direct the examination efficiently.

Clinical Scenario	Common Anatomical Sites	Bronchoscopic Objective
Aspiration	Right lower lobe (RLL)Bronchus intermediusDependent lung segments	Identify and clear aspirated material; assess extent of airway involvement
Mucus	Bronchus intermediusRight middle lobe (RML)Lower lobes	Localise and remove obstructing secretions; assess for distal collapse
Haemoptysis	Variable; may arise from any lung, lobe or segment	Localise bleeding to the affected lung, lobe and segment before further intervention
Difficult Airway Assessment	Vocal cordsSubglottic regionTracheaMain bronchi	Assess airway anatomy, obstruction, stenosis, injury or distortion

Different aspects of anatomy are relevant to different procedures: 

Procedure	Key Anatomy
Intubation	Epiglottis, cords, cricoid
Tracheostomy	Cricoid and tracheal rings
Foreign body retrieval	Right main bronchus, bronchus intermedius
EBUS-TBNA	Carina, stations 4R, 4L, 7, 10 and 11
Transbronchial biopsy	Segmental bronchi
Endobronchial biopsy	Carinae and visible lesions
Bronchial blocker placement	Main bronchi and lobar take-offs

Anatomical variation of the airway and respiratory tract is common. Examples include:

• omega-shaped epiglottis
• prominent arytenoids
• tracheal bronchus
• quadrifurcate RUL branching
• variant lingular branching
• absent left B7
• accessory lower-lobe segments

How to avoid getting lost during bronchoscopy:

• Stop! Do not keep advancing
• Return to the main carina if necessary
• Re-establish orientation – trachea is D-shaped, cartilage is anterior, trachealis/ membrane is posterior.
• Proceed deliberately identifying landmarks as you advance.

Remember the key principles of bronchoscopy orientation.

• The main carina is your compass
• Trachea is D-shaped, cartilage is anterior, trachealis/ membrane is posterior.
• Upper lobes branch superiorly
• Lower lobes branch inferiorly
• Right main bronchus is short, wide and vertical
• Left main bronchus is long, narrow and horizontal
• The anterior bronchus intermedius wall becomes the RML; the posterior wall becomes the RLL.
• Lingula is conceptually the left middle lobe.
• the superior (B6 or apical) segmental bronchi of the lower lobes are posterior
• Normal variation is common.
• If lost, return to the carina and start again.

Useful videos

Rich Levitan’s lecture on anatomy for emergency management of the airway:

The Bronchoscopy Academy has produced a number of useful videos for understanding airway and bronchoscopic anatomy.

Upper airway and larynx:

Abnormal upper airway:

Trachea:

Trachea abnormalities:

Bronchi:

Anatomy variants:

Conclusion

Finding relevant anatomy and maintaining orientation is critical to successful bronchoscopy and other airway management procedures

• Different aspects of anatomy are relevant to different airway and bronchoscopy procedures
• Anatomical variation is common, however :red flags: for pathology must be identified
• A deliberate approach to airway procedures and bronchoscopy, with identification of landmarks as you go, leads to success

References and Links

LITFL

• CCC – Flexible Bronchoscope
• CCC – Bronchoscopic anatomy 
• CCC – Bronchoscopic Foreign Body Removal 
• CCC – Bronchoscopy for Percutaneous Tracheostomy
• CCC – Bronchial blockers 
• CCC – Bronchoalveolar lavage (BAL) 
• CCC – Double lumen endotracheal tube (DLT) 
• CCC – Flexible Nasopharyngolaryngoscopy 

Journal articles 

• Coleman L, et al. Functional anatomy of the airway. Ch 1 in: Hagberg, C. A. (2017). Hagberg and Benumof’s Airway Management E-Book. Netherlands: Elsevier. [google books]
• Ervik Ø, et al. A New Deep Learning-Based Method for Automated Identification of Thoracic Lymph Node Stations in Endobronchial Ultrasound (EBUS): A Proof-of-Concept Study. J Imaging. 2025 Jan 5;11(1):10. doi: 10.3390/jimaging11010010. PMID: 39852323; PMCID: PMC11766424.
• Kavuru MS, et al. Applied Anatomy of the Airways. Ch 4 in Flexible Bronchoscopy, Third Edition, Editors: Wang KP, Mehta AC, Turner Jr JF, Wiley, 2012. [google books]
• Shah P. Atlas of Flexible Bronchoscopy, CRC Press, 2011 [google books]

FOAM and web resources

• Thoracicanaesthesia.com – Virtual bronchoscopy simulator