How to differentiate 2R (right upper paratracheal lymph nodes) and 4R (right lower paratracheal lymph nodes) in Endobronchial Ultrasound (EBUS)?

Differentiating 2R and 4R Lymph Node Stations in EBUS

The key anatomical landmark to differentiate 2R (right upper paratracheal) and 4R (right lower paratracheal) lymph nodes during EBUS is the azygos vein, with 2R being located above the azygos vein and 4R below it. 1

Anatomical Landmarks and Identification

• The right paratracheal lymph nodes are divided into upper (2R) and lower (4R) stations, both of which are accessible via EBUS-TBNA 1
• Station 2R is located above the level of the azygos vein, while station 4R is located below the azygos vein but above the upper border of the left main pulmonary artery 1
• Both stations are adjacent to the trachea, making them accessible for sampling with EBUS-TBNA 1

Technical Considerations for Visualization

• When performing EBUS, the placement of an endotracheal tube may block the ultrasonographic view of higher paratracheal lymph nodes including station 2R, and should be avoided if these nodes are the sampling target 1
• For optimal visualization of station 2R, consider using an oral approach without an artificial airway or with a laryngeal mask airway positioned carefully to avoid obstructing the view 1
• The EBUS scope should be positioned at the appropriate level of the trachea to visualize the azygos vein, which serves as the critical landmark 1

Procedural Tips

• During EBUS examination, first identify the azygos vein on the right side of the trachea using ultrasound with color Doppler to confirm vascular flow 1
• For station 2R examination, position the EBUS scope in the upper trachea above the level of the azygos vein 1
• For station 4R examination, position the scope below the level of the azygos vein but above the main carina 1
• Both stations are more easily accessible via the endobronchial route (EBUS-TBNA) rather than the esophageal route (EUS-B-FNA), as the trachea lies between the esophagus and these lymph node stations 1

Common Pitfalls and Challenges

• Station 2R can be difficult to access if using an endotracheal tube for airway management during the procedure 1
• Stations 2R and 4R are difficult to reach via the esophageal approach (EUS-B-FNA) because the trachea lies between the transducer and the lymph nodes, limiting visualization 1
• In some cases of large lymph nodes (>2 cm), visualization and sampling of stations 2R and 4R may be possible via the esophageal approach despite these limitations 1
• Avoid confusing anatomical structures such as vascular structures or pericardial recesses with lymph nodes by using color Doppler to identify blood vessels 2

Clinical Relevance

• Accurate identification of lymph node stations is critical for proper lung cancer staging according to the International Association for the Study of Lung Cancer (IASLC) lymph node map 1
• Proper differentiation between 2R and 4R has prognostic implications, as involvement of different nodal stations affects the TNM staging of lung cancer 1
• EBUS-TBNA has high diagnostic yield (>90% for adequate samples) for accessible mediastinal lymph nodes, including stations 2R and 4R 3

By following these anatomical landmarks and technical considerations, clinicians can accurately differentiate between 2R and 4R lymph node stations during EBUS procedures, ensuring proper staging and diagnosis for patients with suspected lung cancer or mediastinal pathology.