Pneumothorax on the chest X-ray
- Finding
Air leaks into the space around the lung and the lung pulls away from the chest wall. The X-ray shows a thin white line with no lung pattern beyond it.
What it is
A pneumothorax is air in the pleural space. On an upright chest X-ray the air rises to the apex: one sees the visceral pleura as a thin, sharp white line, with no lung markings between that line and the chest wall. On a supine film, as in trauma, the air collects in front and at the base instead, so the signs are subtle: an unusually deep, dark costophrenic angle (deep sulcus sign), a lucent hemithorax and a very sharp heart or diaphragm edge. Tension pneumothorax pushes the mediastinum away and flattens the diaphragm, but it is a clinical diagnosis to treat at once, not one to confirm on film.
What it looks like
- Visceral pleural line: a thin white line, parallel to the chest wall, with no vessels beyond it.
- Upright film: look at the apices first, where the air collects.
- Supine film: deep sulcus sign, hyperlucent hemithorax, unusually sharp heart border or hemidiaphragm.
- Tension: mediastinum and trachea shifted away, flattened or inverted hemidiaphragm, widened rib spaces.
- Size (British guidance): a rim of air of 2 cm or more at the level of the hilum is large; American guidance measures apex to dome, 3 cm or more.
Why it looks that way
- Air in the pleural space lets the lung recoil toward the hilum, so the pleural edge becomes visible against air on both sides.
- Air rises: upright it goes to the apex, supine it goes to the front and the base of the chest.
- In tension, a one-way valve traps air with each breath; rising pressure shifts the mediastinum and kinks venous return.
Differential and pitfalls
- Skin fold: a broad edge rather than a thin line, often running beyond the chest wall, with lung markings on both sides.
- Large bullae in emphysema mimic a pneumothorax; their wall is concave to the chest wall. CT separates them before any drain.
- The medial edge of the scapula, clothing and tubes can mimic a pleural line; trace it to its end.
- A small or supine pneumothorax is often missed on X-ray; CT is the most sensitive and lung ultrasound helps at the bedside.
- Lung ultrasound: absent lung sliding and no B-lines suggest it; finding the lung point confirms it.
Next step
- Suspected tension (hypotension, distress, shift): decompress at once and call a senior; do not wait for an X-ray.
- Stable patient: size on the upright film plus symptoms and lung disease decide observation, aspiration or a chest drain.
- Unclear pneumothorax versus bulla, or a supine trauma film with doubt: CT of the chest.
- Bedside in trauma or the critically ill: lung ultrasound (eFAST) can show it before the X-ray.
- After aspiration or drain insertion: repeat the chest X-ray to check re-expansion and the drain position.
Test yourself
Think of the answer, then tap the question to see it.
What is the deep sulcus sign?
On a supine film, an abnormally deep and dark lateral costophrenic angle from air collecting at the front and base of the chest: a sign of pneumothorax.
How do you tell a skin fold from a pneumothorax on the X-ray?
A skin fold is a broad edge, often extends beyond the chest wall and has lung markings on both sides; a pneumothorax is a thin line with no markings beyond it.
Should a chest X-ray be taken before treating a suspected tension pneumothorax?
No. Tension is a clinical diagnosis; decompress immediately and image afterwards.
Which lung ultrasound finding confirms a pneumothorax?
The lung point: the place where sliding lung meets the non-sliding air, seen at the edge of the pneumothorax.
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: Acute Pneumothorax Evaluation and Treatment (StatPearls (NCBI Bookshelf), 2025); Tension Pneumothorax (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.