The widened mediastinum and the hila
- Finding
The middle of the chest X-ray holds the heart, great vessels, airway and lymph nodes; if it looks too wide, think of the aorta, a mass or the technique.
What it is
The mediastinum is the central compartment of the chest between the two pleural cavities, from the thoracic inlet to the diaphragm; it holds the heart, the great vessels, the trachea, the oesophagus, the thymus and lymph nodes. On the chest X-ray it is judged by its width and its contours. A width over about 6 cm on an upright PA film, or over about 8 cm on a supine AP film, measured at the level of the aortic knob, is called widened, but technique matters a lot: a supine, AP, rotated or expiratory film magnifies it. True widening comes from the aorta (dissection, aneurysm, traumatic injury with mediastinal blood), from masses (the anterior «4 Ts»: thymoma, teratoma and germ cell tumours, thyroid, terrible lymphoma), from lymph nodes, or from fat. The hila are the roots of the lungs, made mostly of the pulmonary arteries and veins with bronchi and nodes; the left hilum usually sits higher than the right, and both should be of similar size and density.
What it looks like
- Widened: over about 6 cm on an upright PA film or about 8 cm on a supine AP film, at the aortic knob.
- Aortic injury signs: blurred or lost aortic knob, trachea or nasogastric tube pushed right, left main bronchus pushed down, left apical cap.
- Hila: the left is higher than the right in most people; each hilum should taper into vessels.
- A dense, lumpy or large hilum suggests nodes or a mass; large tapering hila on both sides suggest enlarged pulmonary arteries.
- Hilum overlay sign: if hilar vessels are still seen through a mass, the mass is in front of or behind the hilum, not in it.
- Cervicothoracic sign: a mass whose edge stays sharp above the clavicles is posterior; an anterior mass loses its edge there.
Why it looks that way
- The film is a shadow: AP projection, a short distance to the tube and lying flat all enlarge the mediastinum without disease.
- Blood, tumour or nodes push the mediastinal lines out and erase normal contours (silhouette sign).
Differential and pitfalls
- Trauma or tearing chest pain with a wide mediastinum: aortic injury or dissection until proven otherwise; a normal film does not exclude it.
- Anterior mass: thymoma, teratoma and germ cell tumours, retrosternal thyroid, lymphoma.
- Middle mass: lymph nodes (lymphoma, tuberculosis, sarcoidosis, metastases), bronchogenic or other cysts, aortic aneurysm.
- Posterior mass: neurogenic tumours, paravertebral collections, oesophageal lesions, hiatus hernia.
- Bilateral symmetric hilar nodes: sarcoidosis, also lymphoma; one large hilum: lung cancer, tuberculosis, lymphoma.
- Pitfalls: supine AP and rotated films, an unfolded aorta in older patients, mediastinal fat, and the normal thymus in young children.
Next step
- Compare with previous films: a stable contour over years is reassuring; a new one needs explanation.
- Suspected aortic dissection or traumatic aortic injury in a stable patient: urgent CT angiography of the chest and call the senior and surgery.
- Unstable patient with suspected dissection: bedside echocardiography and the senior or surgical team at once; do not send to a distant scanner.
- Mediastinal mass or enlarged hilum: contrast CT of the chest, then tissue diagnosis; in a young man with an anterior mass also AFP and beta-hCG.
- Large anterior mass with cough, stridor or breathlessness when lying down: tell anaesthesia before any sedation (risk of airway collapse).
Test yourself
Think of the answer, then tap the question to see it.
Which chest X-ray signs suggest traumatic aortic injury?
A widened mediastinum, loss of the aortic knob contour, trachea or nasogastric tube shifted right, a depressed left main bronchus and a left apical cap.
What are the 4 Ts of an anterior mediastinal mass?
Thymoma, teratoma (and other germ cell tumours), thyroid (retrosternal goitre) and «terrible» lymphoma.
Why can a supine AP film make the mediastinum look wide?
The heart and mediastinum lie far from the detector and close to the tube, so they are magnified; lying flat also distends the veins.
What is the hilum overlay sign?
If the hilar vessels can still be seen through an apparent hilar mass, the mass lies in front of or behind the hilum rather than in it.
Elsewhere in DurgiPedia
Connections
Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Widened Mediastinum (StatPearls (NCBI Bookshelf), 2023); Anterior Mediastinal Mass (StatPearls (NCBI Bookshelf), 2024); Anatomy, Thorax, Mediastinum (StatPearls (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.