The short answer
Atelectasis means part of a lung has collapsed or not fully filled with air. It can follow surgery, anesthesia, bed rest or shallow breathing, or come from a blocked airway, fluid, or a tumor. Mild atelectasis often causes no symptoms. Trouble breathing needs prompt care.
Atelectasis means part of a lung, or rarely all of it, has not fully filled with air.
Common causes include surgery, anesthesia, bed rest, and shallow breathing. A blocked airway, fluid, or a tumor can also cause it.
Mild atelectasis may cause no symptoms. Tell your care team right away about trouble breathing, chest pain or cough. Call 911 for severe trouble breathing.
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This page is for people whose chest x-ray or CT report mentions "atelectasis." It explains what the word means, common causes, and what to ask your care team.
What atelectasis means
The lungs are made of tiny air sacs. Atelectasis means some of those sacs have not filled with air, so part of the lung is collapsed. MedlinePlus notes that it usually affects part of a lung, and much less often all of it.
NCI's dictionary defines it as failure of the lung to expand completely. It is sometimes called a collapsed lung.
Common causes
MedlinePlus and NCI list many causes. Some of the most common are:
- Surgery and general anesthesia.
- Long bed rest or shallow breathing.
- A mucus plug or something else blocking an airway.
- Fluid around the lung pressing on it.
- A tumor pressing on the lung or blocking an airway.
- Pneumonia or other lung infections.
MedlinePlus notes that atelectasis is common after surgery or in people who are or were in the hospital.
Symptoms
Mild atelectasis may cause no symptoms. When there are symptoms, they can include trouble breathing, chest pain, or cough.
MedlinePlus advises contacting your provider right away if you develop symptoms. For severe trouble breathing, call 911.
What this word cannot tell you
Atelectasis describes how the lung looks. It does not say by itself what caused it. Your care team looks at your history and other findings to decide if anything more is needed.
Ask these before you leave
- Where is the atelectasis, and how large is it?
- What is the likely cause?
- Does it need treatment or a follow-up scan?
- Which symptoms should I report right away?
Related pages
See What Does Pleural Effusion Mean on a Scan?, What Does Pulmonary Nodule Mean?, and X-Ray vs CT Scan
Sources
Common questions
Is atelectasis cancer?
No. Atelectasis describes lung tissue that is not filled with air. Many things can cause it. A tumor blocking an airway is one possible cause.
Is atelectasis serious?
MedlinePlus says a small area of collapse in an adult is usually not life-threatening, because the rest of the lung makes up for it. A large area, or collapse in someone with lung disease, can be serious.
How is atelectasis found?
MedlinePlus lists a physical exam, chest x-ray, CT or MRI, ultrasound, and bronchoscopy as ways to confirm it and look for the cause.
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Sources last checked: 2026-09-27 what this meansLast updated: 2026-10-01Next planned review: 2027-09-27
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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