The short answer
A "ground-glass opacity" (GGO) is a hazy, gray area on a lung CT scan where you can still see the lung markings through it. It has many possible causes — infection, inflammation, scarring, and sometimes early tumors. A GGO is a finding to follow up, not a diagnosis. Radiologists and your doctor decide on next steps, often a repeat scan after a period of time.
A ground-glass opacity is a hazy area on a lung CT — a description, not a diagnosis.
Common causes include infection and inflammation; most GGOs are not cancer.
Follow-up often means a repeat scan later to see whether it changes.
Only your care team, with the full picture, can say what yours means.
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The full explanation.
What ground-glass opacity looks like
Ground-glass opacity, often shortened to GGO, describes a hazy area on a lung CT scan. The lung tissue looks cloudy instead of clear. You can still see the blood vessels and airways through it, the way you can see shapes through frosted glass. This is different from a solid nodule. There, the area is completely opaque. It blocks the view of what is behind it.
Two kinds: pure and part-solid
Radiologists split these findings into two groups, because they carry different risk.
A pure ground-glass nodule is hazy all the way through. It has no solid component anywhere inside it. In a large lung cancer screening study, about 18% of pure ground-glass nodules turned out to be malignant.
A part-solid nodule has a hazy portion and a denser, solid portion together. These carry meaningfully higher risk. In that same screening study, about 63% of part-solid nodules were malignant. The solid portion is the part radiologists watch most closely. It often reflects the more aggressive part of any cancer present.
Why ground-glass nodules get watched differently than solid ones
Ground-glass and part-solid nodules often grow much more slowly than solid nodules. Sometimes this takes years, not months. Because of this, current guidance calls for a longer follow-up window than solid nodules get. Solid nodules often get an early check at a few months. Ground-glass nodules are different. First follow-up is now usually recommended at 6 to 12 months, with continued monitoring for up to five years total. This reflects real evidence. Some ground-glass cancers are slow, early forms of lung adenocarcinoma. They behave very differently from typical fast-growing lung cancer. Rushing to treat them can sometimes cause more harm than watching carefully.
What ground-glass opacity does not tell you
A ground-glass appearance by itself does not tell you what caused it. It could be cancer, infection, inflammation, or bleeding into the lung tissue. Many ground-glass opacities are temporary. They relate to a recent infection or inflammation, and disappear entirely on a follow-up scan. This is part of why an isolated finding on a single scan often gets rechecked before anyone assumes it is anything serious, especially soon after any respiratory illness.
Why persistence matters most
One factor separates a worrying ground-glass opacity from a harmless one more than any other: whether it is still there weeks or months later. A ground-glass finding that resolves on a follow-up scan was very likely infection or inflammation. One that persists is what prompts closer evaluation, sometimes including biopsy. This matters most if it grows or develops a solid component over time.
What to ask your team
- Is my finding pure ground-glass, or does it have a solid component?
- Has this been seen on a prior scan, or is it new?
- What is the recommended follow-up schedule, and how long will I need monitoring?
- What changes on a future scan would prompt a biopsy?
Sources
Words to know
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Common questions
Does a ground-glass opacity mean lung cancer?
Not usually. GGOs have many causes, and infections or inflammation are common. Some persistent GGOs can represent early tumors, which is why doctors track them over time rather than ignoring or panicking about them.
Why does my doctor want another scan later?
Comparing scans over time shows whether a GGO resolves, stays the same, or grows. That pattern is one of the most useful clues to its cause and guides whether anything more is needed.
Questions to ask your doctor
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Last updated: 2026-08-18Next planned review: 2027-07-12
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How this page was created
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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. 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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