Atelectasis seen by chance on a chest scan

What the report means

Linear or plate-like. A thin strip or band of lung that is not fully open. The current glossary calls it "linear"; older reports may say "plate-like" or "band-like". It is often seen in the lower parts of the lungs, along the diaphragm on an X-ray or the chest wall on CT. (Fleischner 2024)
Subsegmental or segmental. Names for how big the area is: a small part of a lung segment, or a whole segment. Subsegmental atelectasis often looks linear. (Fleischner 2024)
Dependent. The area sits in the lowest part of the lungs at the time of the scan, usually the back when you lie face up. Lying flat lowers the amount of air in the lungs, and the weight of the lungs, heart and belly presses on these parts. (Zeng 2022)
Rounded. A rarer, rounded area next to thickened lining of the lung, linked to long-standing or recurring fluid around the lung, asbestos exposure, heart or kidney failure or cancer in the chest. It is most often in the lower back part of the lungs. (Fleischner 2024)(Sobocinska 2014)
Lobar. A whole lobe of the lung not open is a bigger finding than the small areas this page is about. (Fleischner 2024)

When it is seen more

Causes. The glossary lists loss of the normal suction around the lung, pressure on the lung (for example from fluid around it), air being absorbed behind a blocked airway, and changes in the lining fluid of the air sacs. (Fleischner 2024) If the report also mentions fluid around the lung, see small fluid around the lung seen by chance.
Around surgery. Atelectasis is common around surgery. Under general anaesthesia, CT showed it in about 90% of adults with no heart or lung disease, almost always in the lower, back parts of the lungs. (Zeng 2022)(Lagier 2022) Upper belly surgery and heart and chest surgery raise the risk. (Lagier 2022)
Body weight. A higher body weight raises the risk around surgery. (Lagier 2022) In a pooled CT study of 243 adults under anaesthesia, the area rose with body mass index up to 30 and did not rise further above that. (Hedenstierna 2020)
Age. In the same study of adults aged 18 to 78, the area was largest at about 50 and smaller after that. (Hedenstierna 2020)(Lagier 2022) This was measured under anaesthesia; we found no open study giving how often small areas are seen on everyday scans at each age.

How reports tell it apart from scarring or a nodule

Signs of lost volume. Atelectasis is smaller and denser than normal lung and often pulls the nearby lung divisions, airways or blood vessels toward it. (Fleischner 2024)
Scarring. The glossary uses separate terms for lasting changes, such as a "parenchymal band", a thin line along the lining of the lung that is often seen after asbestos exposure and also described after some pneumonias, including COVID-19. (Fleischner 2024) For scarring or haziness reports, see lung scarring seen by chance.
Rounded atelectasis and a nodule. Rounded atelectasis usually causes no symptoms and is often first noticed by the radiologist. It can be mistaken for lung cancer, but typical CT signs (next to thickened lung lining, vessels and airways curving into it like a "comet tail", and a smaller lobe) usually allow it to be recognised on CT. Follow-up scans up to a year often show no change. (Sobocinska 2014)
X-ray limits. Small areas low down at the back or behind the heart can be missed on a front-view chest X-ray. CT is the reference test and can also show a cause, such as a blocked airway or fluid around the lung. (Lagier 2022)
Other findings. If the report names a small calcified spot or a thin-walled air space instead, see calcified lung granuloma seen by chance or lung cyst seen by chance.

Signs that need help

Urgent NHS 111. The NHS lists difficulty breathing or being more short of breath than usual, coughing up blood, pain or swelling in one leg, and heart palpitations. (NHS)
See a GP. The NHS lists shortness of breath that gets worse with normal activities or when lying down, shortness of breath with swollen ankles, and a cough that has lasted 3 weeks or more. (NHS)
Worry is real. See after an abnormal screening result.

The NHS says to call 999 or go to A&E if you have severe difficulty breathing (gasping, choking or not able to get words out), your chest feels tight or heavy, pain spreads to your arms, back, neck and jaw, your lips or skin turn very pale, blue or grey, or you feel suddenly confused. (NHS)

In the US, the emergency number is 911.

How it ties to your age-based checks

A chest scan done for another reason does not replace lung cancer screening. The USPSTF recommends a yearly low-dose CT for adults aged 50 to 80 who have a 20 pack-year smoking history and smoke now or quit within the past 15 years. (USPSTF 2021)

Who it applies to

Adults told that a chest CT or X-ray done for another reason shows a small area of atelectasis. Children, people in hospital with breathing trouble, people recovering from surgery under a care team, and people told a whole lobe or lung has collapsed are outside this page.

Routine age-based screening

A finding on a scan does not replace the routine screenings for your age. See screenings by age and gender.

Where they differ:

Names. The Fleischner glossary now prefers "linear" over the older "plate-like" or "band-like", and notes that the strip only looks like a line in one slice; reports from different places may still use the older words for the same thing. (Fleischner 2024)
Age. Small airways close more easily with older age, yet under anaesthesia the area of atelectasis was largest at about 50 and smaller in older adults; the review suggests airway closure itself may slow the collapse. (Lagier 2022)(Hedenstierna 2020) These studies were done around surgery, not on everyday scans.
When a strip matters. Linear atelectasis is often seen low in the lungs (Fleischner 2024), but one X-ray study found that a thick strip near the lung root (over 5.5 mm) was often caused by a lung tumour blocking an airway, and that a strip that does not go away can be a sign of cancer. (Ozturk 2018) That is a single study.
Rounded areas. One review says rounded atelectasis can usually be recognised on CT alone, but also that it can be mistaken for cancer when the typical signs are not all there. (Sobocinska 2014)

Your doctor decides what your result means for you.

Questions people ask

Is atelectasis the same as a collapsed lung?

The words mean the same thing: part of the lung, or all of it, is not fully filled with air. On a scan done for something else it is usually a small strip or patch, not the whole lung. (Fleischner 2024)

Why does my scan show atelectasis?

Small areas are often seen in the lower, back parts of the lungs, which take the weight of the lung and belly when you lie flat. Pressure from fluid around the lung or a blocked airway can also cause it. (Fleischner 2024) (Zeng 2022)

I just had surgery. Is that the reason?

It can be. Atelectasis is common around surgery: in studies of adults without heart or lung disease, CT showed it in about 9 in 10 people under general anaesthesia, mostly in the lower, back parts of the lungs. (Zeng 2022) (Hedenstierna 2020)

Could it be cancer?

In one X-ray study of strips near the lung root, most had other causes, but thick strips were often caused by a tumour blocking an airway, and one review says rounded atelectasis can be mistaken for lung cancer. Your doctor decides whether anything more is needed. (Ozturk 2018) (Sobocinska 2014)

Is it the same as lung scarring?

Not quite. Atelectasis means lung that is not fully filled with air. The glossary radiologists use lists lasting line-like changes, such as a parenchymal band, under a separate term. (Fleischner 2024)

Small collapsed lung area (atelectasis) seen by chance on a scan