Mediastinum and hila on chest X‑ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

The mediastinum is the central compartment of the chest, containing the heart, great vessels, trachea, oesophagus, thymus and lymph nodes. The hila are where the bronchi, pulmonary arteries and veins enter each lung. Both are hard to read because they are made of overlapping soft-tissue structures, and because their appearance changes with projection, rotation and age. Yet they hide some of the most important diagnoses on a chest film: aortic injury after trauma, aortic dissection, lymphoma, central lung cancer and sarcoidosis. This page teaches the normal contours, how to judge widening, how to localise a mass to a compartment, and how to approach an abnormal hilum.

1. Normal contours

On a well-centred PA film, trace the edges of the mediastinum from top to bottom on each side. See also normal chest X-ray anatomy.

• Right side: the SVC and right brachiocephalic vein above, then the right atrium forming the right heart border. The right paratracheal stripe, the thin line of soft tissue between the tracheal air column and the right lung, is normally no more than about 4–5 mm wide.
• Left side: the left subclavian artery above, then the aortic knob (arch), the aortopulmonary (AP) window (normally a concave notch), the main pulmonary artery, the left atrial appendage (usually flat) and the left ventricle.
• Lines and stripes that may be visible: the anterior and posterior junction lines, the paraspinal lines (the left is usually wider than the right), and the azygo-oesophageal line behind the heart.

Loss of a normal line or a bulge in a normal contour is often the earliest sign of disease.

2. The widened mediastinum

Because the numbers are unreliable, many readers rely more on the contours: is the aortic knob crisp, is the AP window still concave, is the paratracheal stripe thin? Causes of widening include:

• technical: AP projection, supine position, rotation, poor inspiration;
• vascular: unfolded aorta in older people (common and benign), aneurysm, dissection, traumatic aortic injury;
• haemorrhage: trauma, or after central line insertion or cardiac surgery;
• masses and nodes: lymphoma, thymic tumours, retrosternal thyroid, lymphadenopathy;
• fat: mediastinal lipomatosis in obesity or steroid use.

3. Traumatic aortic injury and dissection

Traumatic aortic injury

Blunt aortic injury, usually at the isthmus just beyond the left subclavian artery, follows high-energy deceleration. The chest X-ray signs (ATLS) reflect a mediastinal haematoma:

• widened mediastinum;
• loss or abnormality of the aortic knob contour;
• opacification of the AP window;
• deviation of the trachea, and of an NG tube, to the right;
• depression of the left main bronchus (more than about 40° below the horizontal);
• widening of the right paratracheal stripe (more than about 5 mm) and of the paraspinal lines;
• a left apical cap (blood tracking over the lung apex);
• fractures of the 1st and 2nd ribs, sternum or scapula, which indicate high-energy trauma.

A normal chest X-ray does not exclude aortic injury. When the mechanism is concerning, CT angiography is the test. See chest trauma.

Aortic dissection

Signs include a widened mediastinum, a double or irregular aortic contour, a left pleural effusion, and the calcium sign: intimal calcification displaced inwards from the outer edge of the aortic wall, classically by more than about 5 mm (some sources use up to 10 mm). [VARIES] The chest X-ray is often normal or non-specific in dissection, so it must not be used to rule it out. CT angiography is the test when dissection is suspected.

4. Compartments and masses

Dividing the mediastinum into compartments narrows the differential. The classic Felson scheme uses the lateral film; the newer International Thymic Malignancy Interest Group (ITMIG) scheme defines the compartments on CT as prevascular, visceral and paravertebral.

Compartment	Contents	Common masses
Anterior (prevascular)	Thymus, fat, nodes	The "4 Ts": thymoma, teratoma and other germ-cell tumours, thyroid (retrosternal goitre, which often deviates the trachea), and "terrible" lymphoma
Middle (visceral)	Heart, great vessels, trachea, oesophagus, nodes	Lymphadenopathy, bronchogenic and foregut cysts, aortic aneurysm, hiatus hernia, oesophageal masses
Posterior (paravertebral)	Sympathetic chain, nerve roots, paraspinal tissues	Neurogenic tumours (schwannoma, neurofibroma, ganglioneuroma; neuroblastoma in children), paraspinal abscess, extramedullary haematopoiesis

5. Localising signs

Felson described several signs that help place a mass using only the frontal film:

• Hilum overlay sign: if the hilar vessels can be seen through a mass, the mass is not in the hilum; it lies in front of or behind it (typically anterior mediastinum). If the vessels are obscured, the mass is at the hilum.
• Hilum convergence sign: if the pulmonary vessels converge into the opacity, it is probably an enlarged pulmonary artery. If they pass through or by it without converging, it is more likely a mass.
• Cervicothoracic sign: a mass whose upper border remains sharply visible above the clavicles must be outlined by lung, so it lies posteriorly. An anterior mediastinal mass loses its border at the level of the clavicles, because the anterior mediastinum ends at the thoracic inlet.
• Silhouette sign: a mass that obscures the heart border or the aortic knob is in contact with it.

6. The hila

Normal

• The left hilum is level with or higher than the right in most people. A right hilum that is higher than the left suggests volume loss in the right upper lobe or left lower lobe. See lobar collapse.
• Both hila should be of similar size and density, with a concave lateral outline. A hilum that is denser than the other, or has a convex lobulated outline, suggests a mass or nodes.
• The right descending (lower lobe) pulmonary artery is normally up to about 16 mm wide in men and 15 mm in women. [VARIES]

Bilateral hilar enlargement

• Lymphadenopathy: sarcoidosis (symmetrical bilateral hilar lymphadenopathy, often with right paratracheal nodes: the "1-2-3 sign" or Garland triad), lymphoma, TB, metastases, silicosis.
• Vascular: pulmonary arterial hypertension, with large central pulmonary arteries and "pruning" of the peripheral vessels.

Unilateral hilar enlargement

Think first of bronchogenic carcinoma, then TB, lymphoma, metastases, or post-stenotic dilatation of the pulmonary artery (in pulmonary valve stenosis, affecting the left). See lung nodules and masses and TB.

Node calcification and sarcoid staging

Eggshell calcification of hilar nodes (a thin rim) suggests silicosis or coal-worker's pneumoconiosis, and is also seen in treated lymphoma and sarcoidosis. The Scadding chest X-ray stages of sarcoidosis are: 0 normal; I bilateral hilar lymphadenopathy only; II nodes plus lung changes; III lung changes without nodes; IV fibrosis, typically in the upper zones with hilar retraction. See interstitial lung disease.

7. Pitfalls

• Rotation makes one hilum look larger and widens the mediastinum on one side. Check the clavicles before calling an abnormality.
• The unfolded aorta in older patients widens the upper mediastinum to the right. Compare with old films.
• The thymus in infants and young children is large and can look like a mass. See the neonatal chest X-ray.
• Supine films exaggerate width; never call widening on a supine film without considering technique, and never be reassured by a "normal" width in a trauma patient with a concerning mechanism.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Normal contours, the left hilum higher than the right, the 4 Ts, and bilateral hilar lymphadenopathy in sarcoid.
Nurse	Know that a widened mediastinum after trauma or with chest pain is an emergency that needs a CT, not a repeat film.
Junior doctor	Recognise the trauma and dissection signs, and know the film does not exclude either. Arrange CT angiography and senior review.
Radiographer	Minimise rotation and obtain an erect PA where the patient's condition allows, since supine AP films exaggerate width.
Advanced / FRCR	Mediastinal lines and stripes, Felson's localising signs, ITMIG compartments and the differential of mediastinal masses.

Practise on real chest X-rays →

References

1. Carter BW, et al. ITMIG definition of mediastinal compartments on multidetector CT. J Thorac Oncol 2014;9(9 Suppl 2):S97–S101.
2. American College of Surgeons. Advanced Trauma Life Support (ATLS), 10th edition. 2018.
3. Felson B. Chest Roentgenology. Philadelphia: WB Saunders; 1973.
4. Radiopaedia. Pulmonary sarcoidosis. radiopaedia.org
5. Radiology Masterclass. Chest X-ray anatomy. radiologymasterclass.co.uk
6. Royal College of Radiologists. iRefer. irefer.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.