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Lung cyst seen by chance on a chest CT

A chest CT done for something else, often a lung cancer screening scan, may report a "lung cyst" or "pulmonary cyst". This is a small round air-filled space with a thin wall. One or a few such cysts become more common with age and usually stay the same for years. (Araki 2015)(ACR Lung-RADS v2022) This page covers what the report means and when more checks are listed, not treatment.

What the report means

  • What it is. On CT, a lung cyst is a round, usually thin-walled, darker (air-filled) area with a clear edge against the normal lung around it. (Araki 2015)
  • Found by CT. A CT scan uses special X-ray equipment to make detailed cross-section pictures of the inside of the body. (MedlinePlus) Lung cysts are found more often now because more people have chest CT scans, including for lung cancer screening. (Araki 2015)
  • "Thin-walled" cyst. In the Lung-RADS system for screening scans, a thin-walled cyst has one compartment and an even wall thinner than 2 mm. Such cysts are considered benign and are not classified or managed in Lung-RADS. (ACR Lung-RADS v2022)(Petranovic 2026)
  • Not the same as emphysema. A thin wall helps tell a cyst apart from emphysema, and in one large study the two occurred independently. (Araki 2015)

How common they become with age

  • In a community study. Among 2,633 adults in the Framingham Heart Study with a mean age of 59, 7.6% had at least one lung cyst. (Araki 2015)
  • Rising with age. No one under 40 had a cyst. The share rose from 4.9% at ages 40 to 49 to 12.9% over age 80. People with cysts were older on average, 63 versus 59. (Araki 2015) Smaller earlier studies found cysts in 25% of people over 75 and 13% over 65, and none in younger groups. (Araki 2015)
  • Usually one. Cysts were mostly single, in the outer part of the lower lungs. Five or more cysts were seen in 0.9% of people. (Araki 2015)
  • Not tied to smoking. Cysts were not linked to smoking or emphysema, and they did not change breathing test results apart from one gas transfer measure. (Araki 2015) The study authors suggest single cysts may be part of normal lung ageing. (Araki 2015)

Do they change over time?

  • Mostly stable. In people who had an earlier CT a median of 6.1 years before, 68 cysts were unchanged, 39 had grown by more than 2 mm and 2 had shrunk. Overall, cysts tended to grow slightly with age. (Araki 2015)
  • How growth is measured on screening scans. Lung-RADS counts growth as an increase of more than 1.5 mm in size or wall thickness within 12 months. (ACR Lung-RADS v2022)

When a cyst leads to more checks

  • A single simple cyst. A thin-walled cyst with one compartment is considered benign in Lung-RADS and gets no category of its own. (ACR Lung-RADS v2022) Your screening result then depends on any other findings. See lung cancer screening results.
  • A thick wall or several compartments. Lung-RADS calls these "atypical" cysts. A wall 2 mm or thicker, or a cyst split into several compartments, is category 4A. (ACR Lung-RADS v2022)(Petranovic 2026)
  • A cyst that changes. A thickening or lumpy wall that grows, a multi-compartment cyst that grows, or new haze or a nodule in or next to the cyst is category 4B. (ACR Lung-RADS v2022) A cyst with a nodule next to it is managed by its most concerning feature. (ACR Lung-RADS v2022)
  • European guidance. The European Society of Thoracic Imaging says complex cysts, such as cysts with several compartments, are a specific finding to pick out on screening scans because they are usually related to invasive lung cancer, and they should be checked further. (ESR 2026)
  • Many cysts. Many cysts may point to a different lung condition, such as lymphangioleiomyomatosis (LAM) or Langerhans cell histiocytosis (LCH), and Lung-RADS does not classify them unless other concerning features are seen. (ACR Lung-RADS v2022)(Araki 2015) LAM mainly affects women, with an average age at diagnosis of about 35. (Gupta 2015)
  • Fluid inside. A cyst that holds fluid may be an infection and is not classified in Lung-RADS unless other concerning features are seen. (ACR Lung-RADS v2022)
  • Worry is real. See after an abnormal screening result.

How it ties to your age-based checks

A lung cyst found by chance is a good moment to make sure your routine checks are up to date:

Other chest CT findings have their own pages: widened airways, lung scarring and lung nodule found by chance.

Who it applies to

Adults told that a chest CT done for another reason, or a lung cancer screening scan, shows one or a few lung cysts, with no symptoms from them. Children, people known to have a cystic lung disease and people with a cyst holding fluid are outside this page.

The NHS advises seeing a GP for a cough lasting more than 3 weeks, an urgent GP appointment or NHS 111 if you cough up blood, and calling 999 (911 in the US) or going to A&E if you are struggling to breathe. (NHS)

Routine age-based screening

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

Where they differ:

  • US and European screening wording. Lung-RADS sets a 2 mm wall cut-off and separate categories for thick-walled, multi-compartment and growing cysts. (ACR Lung-RADS v2022) The European Society of Thoracic Imaging names complex cysts as a finding to check further, without the same category steps. (ESR 2026)
  • Ageing or disease. One large study suggests single cysts are part of lung ageing over 40 (Araki 2015), while many cysts, especially in younger women, can point to a cystic lung disease. (Gupta 2015)(Araki 2015)
  • Scans outside screening. Lung-RADS is written for lung cancer screening scans. For a CT done for another reason, ask what the radiologist's report suggests. (ACR Lung-RADS v2022)

Your doctor decides what your result means for you.

Questions people ask

How common is a lung cyst on a CT scan?

In 2,633 adults in the Framingham Heart Study, 7.6% had at least one lung cyst. None were under 40, and the share rose from 4.9% at ages 40 to 49 to 12.9% over 80. (Araki 2015)

Is a thin-walled lung cyst cancer?

In the ACR Lung-RADS system for lung screening scans, a single cyst with an even wall thinner than 2 mm is considered benign and is not given a category. (ACR Lung-RADS v2022)

Will a lung cyst grow?

In the Framingham study, most cysts stayed the same or grew slightly over a median of 6.1 years. (Araki 2015)

Is it linked to smoking?

In the Framingham study, lung cysts were not linked to smoking or to emphysema. (Araki 2015)

When does a cyst lead to more checks?

Lung-RADS lists a wall 2 mm or thicker, several compartments, a growing wall or a nodule next to the cyst as atypical. Many cysts may point to a different lung condition. Your doctor decides. (ACR Lung-RADS v2022) (Araki 2015)

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