What does "atelectasis" mean on my chest X-ray or CT report?
Short answer: a small area of your lung isn't fully expanded. "Atelectasis" (from Greek, roughly "incomplete expansion") means some of the tiny air sacs in part of a lung have partially collapsed or aren't filling with air as they should.
What it usually means on your report
You'll often see phrases like "mild bibasilar atelectasis" (both lower lungs) or "plate-like atelectasis." The most common scenario: you were lying still during the scan — or after surgery, or breathing shallowly because of pain — and the bottom parts of your lungs simply didn't fully inflate. Radiologists describe thin, flat areas of this as "plate-like" or "band-like" atelectasis, and it's frequently incidental.
Atelectasis happens when an airway is blocked (for example by mucus) or when part of the lung is compressed from the outside (for example by fluid around the lung). Small areas are often harmless and temporary; larger areas deserve a closer look from your clinician.
What it does NOT mean
- It does not mean your lung is permanently damaged. Small areas of atelectasis often resolve on their own, especially once you're moving and breathing normally again.
- It does not mean the same thing as pneumonia. On imaging, atelectasis shows volume loss (things shift toward the collapsed area); pneumonia typically doesn't. They can look similar to a non-expert, which is why the radiologist's read matters.
- It does not mean you have a chronic lung disease. Atelectasis is a finding — a description of what the lung looks like right now — not a disease diagnosis.
When to ask your clinician
- "Is this atelectasis likely from how I was positioned/breathing during the scan?"
- "Do I need a follow-up image to confirm it resolved?"
- "Are there breathing exercises or anything I should do in the meantime?"
This is a plain-English explanation of terms, not medical advice. Talk to your clinician about what your results mean for you.