Pneumothorax

What it means

Normally the lung sits snugly against the inside of the chest wall, held in place by a vacuum-like seal in the thin pleural space between them. When air slips into that space — through a tear in the lung surface, a chest injury, or sometimes spontaneously — the seal breaks and the lung partially collapses away from the chest wall. On imaging, the radiologist sees a dark stripe of air where lung tissue should be touching the ribs.

Why it appears on a CT or MRI report

Radiologists describe this finding with care because size and location guide treatment. The report often notes which side it is on (left, right, or both), an estimate of how large the air pocket is (small, moderate, large, or measured in millimetres), whether the lung has collapsed significantly, and whether the heart and trachea are being pushed toward the other side. That last detail — pressure pushing structures over — is the warning sign of a tension pneumothorax.

What it usually means

A small, simple air leak in an otherwise healthy person, often picked up after a fall, a rib fracture, or sometimes for no clear reason in tall thin young adults, can resolve on its own with observation, oxygen, and rest. Moderate leaks usually need a small tube placed between the ribs to let the air out so the lung can re-expand. A large leak, or one where the trapped air is under pressure and pushing the heart sideways, is a medical emergency — that situation is called tension pneumothorax and needs immediate decompression. People with existing lung disease (emphysema, cystic lung disease) are more vulnerable, and even a small leak in those lungs can cause significant breathlessness. The radiologist's wording and the clinical team's judgement go together.

When to follow up

This finding usually prompts action straight away — in most cases your care team will already be on it before you read the report. Seek emergency care if you have sudden one-sided sharp chest pain, sudden shortness of breath, or a feeling that you cannot catch your breath, especially after an injury or procedure. After treatment, follow-up scans are routine to confirm the lung has re-expanded. Avoid flying or scuba diving until cleared by your doctor.

A plain-language way to picture it

Picture a wet suction cup stuck to a smooth window. As long as the seal holds, the cup stays flat and firm against the glass. Poke a tiny hole behind the cup and air sneaks in — the suction breaks, and the cup peels away from the window. The lung does the same thing: it relies on a quiet vacuum to stay open against the chest wall, and any air in the wrong place lets it fall away.