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Radiology · Chest Radiology

Mediastinal lymph nodes

Nodi lymphatici mediastinales

Mediastinal lymph nodes do not have clear anatomical boundaries, so in diagnostic imaging they are divided into groups strictly by localization. The generally accepted standard is the international IASLC map, which distinguishes 7 zones and 14 stations for precise staging of pathological processes in the chest.

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IASLC SystemDistinguishes 7 anatomical zones and 14 stations. Used in the TNM classification for lung cancer.
Paratracheal stripeNormally, its thickness on a radiograph should not exceed 5 mm. Individual nodes are not visible here.
Pleural reflection linesTheir presence rules out space-occupying lesions, but their absence is not a sign of disease.
Azygos veinServes as an important landmark. Normally, its diameter at the tracheobronchial angle does not exceed 10 mm.
5 min readFor medical studentsUpdated Sep 25, 2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

IASLC Classification and Anatomical Zones

For the convenience of prognostic analysis, the International Association for the Study of Lung Cancer (IASLC) has combined lymph node stations into 7 anatomical zones:

  1. Supraclavicular zone (Station 1): Covers right (1R) and left (1L) nodes. Extends from the cricoid cartilage down to the clavicles and the upper edge of the manubrium sterni.
  2. Upper zone (Stations 2–4): Includes upper paratracheal nodes (2R, 2L) located above the aortic arch or above the intersection of the brachiocephalic vein with the trachea. Prevascular nodes (3a) lie anterior to the great vessels, and retrotracheal nodes (3p) lie posterior to the trachea. Lower paratracheal nodes (4R, 4L) are localized below the upper border of the aortic arch.
  3. Aortopulmonary zone (Stations 5, 6): Combines paraaortic nodes and nodes of the aortopulmonary window.
  4. Subcarinal zone (Station 7): Bifurcation nodes lying within the mediastinal pleura directly below the tracheal carina.
  5. Lower zone (Stations 8, 9): Extends down to the diaphragm. Includes paraesophageal nodes (along the esophagus) and pulmonary ligament nodes.
  6. Hilar zone (Station 10): Hilar nodes adjacent to the main bronchi and the vessels of the lung roots.
  7. Peripheral zone (Stations 11–14): Interlobar, lobar, segmental, and subsegmental nodes located along the bronchial tree.

Radiological Anatomy and CT Landmarks

In CT examination, lymph node visualization relies on major vascular and airway structures. International abbreviations are used on tomograms: Ao (aorta), Az (azygos vein), Eso (esophagus), SVC (superior vena cava), T (trachea).

Important anatomical landmarks of the mediastinum:

  • Thymus (Thymus): In the anterior mediastinum of young patients, glandular tissue is clearly defined. With age, involution occurs—only connective tissue strands against the background of fatty tissue remain on scans.
  • Esophagus (Oesophagus): Traced on all axial slices from the thoracic inlet to the diaphragm. In a collapsed state (without air), it has a minimum diameter of about 1 cm. On MRI, its signal intensity on T1-weighted images is similar to muscle, and on T2-weighted images it is significantly higher.
  • Azygos vein (v. azygos): Outlined by air in the right lung. Azygos nodes are located directly beneath it, but are not normally differentiated on a radiograph.
  • Right paratracheal stripe: A uniform zone between the tracheal air column and the right lung, consisting of the tracheal wall and adjacent fat. The presence of a clear stripe (up to 5 mm thick) rules out a localized space-occupying process. Normally, individual nodes here do not cause focal bulges.
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Radiographic Appearance and Pleural Reflection Lines

Plain chest radiography provides very limited information about mediastinal structures. Mainly only the interfaces (borders) between the aerated lung tissue and soft tissues are visualized. Pleural reflection lines play a key role:

  • Anterior junction line: Formed by the apposition of the lungs anterior to the ascending aorta (the total thickness consists of just over 4 layers of pleura). The line diverges in a cranial direction and is never visible above the level of the clavicles. Inferiorly, it descends for a variable distance, arching around the right ventricular outflow tract.
  • Posterior junction line: Formed by the apposition of the lungs posterior to the esophagus. Unlike the anterior line, it continues high up to the lung apices (significantly higher than the medial ends of the clavicles). Caudally, the line diverges, arching around the aortic arch, but may re-approximate below it.

Diagnostic value of these lines lies in the fact that their clear visualization reliably rules out a pathological space-occupying process in these areas. However, since they are not visible in all healthy individuals, their absence is not a sign of pathology.

Briefly: answers to topical questions

What are the upper and lower boundaries of the lower paratracheal lymph nodes (stations 4R and 4L)?

The upper and lower boundaries of the lower paratracheal lymph nodes depend on the side of their location.

  • Right lower paratracheal nodes (station 4R) — the upper boundary runs at the level of the intersection of the caudal edge of the brachiocephalic vein with the trachea, and the lower boundary corresponds to the lower edge of the azygos vein (v. azygos).
  • Left lower paratracheal nodes (station 4L) — the upper boundary is located at the level of the upper edge of the aortic arch, and the lower boundary reaches the upper edge of the left main pulmonary artery.

What are the exact anatomical boundaries of the subaortic (station 5) and paraaortic (station 6) lymph nodes?

The anatomical boundaries of these stations are defined relative to the aortic arch and pulmonary artery.

  • Subaortic nodes (station 5) — located lateral to the ligamentum arteriosum; their upper boundary runs along the lower edge of the aortic arch, and the lower boundary corresponds to the upper edge of the left main pulmonary artery.
  • Paraaortic nodes (station 6) — lie anterior and lateral to the ascending aorta and its arch; the upper boundary is defined by a line tangent to the upper edge of the aortic arch, and the lower boundary runs along the lower edge of the aortic arch.

Class and exam questions

What is the IASLC classification and what is it used for?

This is an international system of topographic mapping of chest lymph nodes. It is necessary for standardization and precise clinical staging of lung cancer according to the TNM system.

Where are station 7 lymph nodes located and how to find them on CT?

Station 7 lymph nodes (subcarinal) are located in the mediastinal tissue strictly below the tracheal bifurcation (carina). The lower boundary for them is formed by the upper edges of the lower lobe bronchus on the left and the intermediate bronchus on the right.

What does thickening of the right paratracheal stripe on a radiograph indicate?

Thickening of the stripe greater than 5 mm or the appearance of focal bulges on it indicates a pathological space-occupying process. Normally, lymph nodes in this zone merge with the mediastinal fat and do not alter the contour of the stripe.

Why is the absence of the anterior pleural junction line on a scan a variant of normal?

Both pleural reflection lines are inconsistently visible and depend on the individual amount of mediastinal fat and the patient's anatomical features. Therefore, their invisibility has no independent diagnostic significance.

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What else to study on this topic

  • Detailed anatomical boundaries of each station from 1 to 14 according to the IASLC table
  • Specifics of MRI semiotics of the esophagus and mediastinal structures on T1- and T2-weighted images
  • Topographic relationships of lymph nodes with great vessels (aorta, pulmonary artery, superior vena cava)
  • Age-related involution of the thymus gland and differential diagnosis of anterior mediastinal masses
  • Anatomical differences of the right interlobar node subgroups (11s and 11i)

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