Ground-Glass Opacity vs Solid Lung Nodule: What’s the Difference?

Ground-glass opacities (GGOs) and solid nodules are two of the most common findings on chest CT scans in Korea. Although they may look similar on a radiology report, they behave very differently and require different follow-up strategies.
This guide breaks down the key differences to help patients understand their lung CT results.

What Is a Ground-Glass Opacity (GGO)?

A ground-glass opacity is a hazy, translucent area on CT where the underlying lung structures—such as tiny blood vessels—are still visible.
It looks “foggy,” not dense.

Common Causes of GGOs

• Prior infection or inflammation
• Post-radiation or post-surgery changes
• Fibrosis or scar tissue
• Early adenocarcinoma
• Benign inflammatory nodules

Risk Level of GGOs

Pure GGOs are usually lower risk compared to solid nodules.
They tend to grow slowly and often remain stable for years.

Typical Follow-Up for GGOs in Korea

• Repeat CT in 6–12 months
• If stable, annual low-dose CT
• Continue monitoring for any changes in size or density
• 
  

What Is a Solid Pulmonary Nodule?

A solid nodule is a dense, opaque spot that completely blocks the visibility of lung vessels behind it.
This “solid” appearance makes it more concerning than a GGO.

Common Causes of Solid Nodules

• Old infections (granulomas)
• Benign fibrosis or scars
• Primary lung tumors
• Metastatic nodules (if cancer history exists)

Risk Level of Solid Nodules

Solid nodules have a higher likelihood of malignancy, especially if:

• They grow >2 mm
• They have irregular or spiculated borders
• They are larger than 8 mm

Follow-Up for Solid Nodules in Korea

• Repeat CT in 3–6 months depending on size
• PET-CT or biopsy for nodules >8 mm
• Closer monitoring if risk factors are present



Ground-Glass Opacity vs Solid Nodule: Key Differences

FeatureGround-Glass Opacity (GGO)Solid Lung NoduleAppearanceHazy and translucentDense and opaqueCan you see vessels through it?YesNoCancer riskLowerHigherGrowth rateVery slowFasterCause rangeInflammation → early cancerScarring → solid tumorFollow-up intensityModerateMore aggressiveWhen concerning?If density or solid component appearsIf >8 mm or growing

What About Part-Solid Nodules? (Most Concerning)

A part-solid nodule contains both:

• A ground-glass region
• A solid internal core

This type carries the highest risk among nodule types and often represents early-stage lung adenocarcinoma.

Follow-Up for Part-Solid Nodules

• Repeat CT at 3 months
• Consider PET-CT or biopsy if the solid part persists
• Closer surgical evaluation depending on size

Which One Is More Likely to Be Cancer?

From lowest to highest risk:

1. Pure GGO (stable for years)
2. Small solid nodule (<6 mm)
3. Growing solid nodule
4. Part-solid nodule (highest risk)

Solid and part-solid nodules require more aggressive evaluation because they represent denser, more mature tissue.

Key Takeaways

• Ground-glass opacity = hazy, lower risk, slow growing.
• Solid nodule = dense, higher risk, needs closer follow-up.
• Part-solid nodule = highest concern and needs careful evaluation.
• Stability over time is one of the strongest predictors of safety.
• Korean hospitals typically use low-dose CT for long-term monitoring.