What is a pulmonary nodule?

What is a Pulmonary Nodule?

A pulmonary nodule is a small, rounded spot on the lung that appears on imaging—specifically, a well-circumscribed radiographic opacity up to 3 cm in diameter that is completely surrounded by normal lung tissue, without associated collapse of lung tissue (atelectasis), enlarged lymph nodes at the lung root (hilar enlargement), or fluid around the lung (pleural effusion). 1, 2

Key Characteristics You Should Know

Size Matters

• Nodules are defined as lesions up to 3 cm (30 mm) in diameter 1, 2
• Anything larger than 3 cm is called a lung mass and is considered lung cancer until proven otherwise 1, 2
• Most nodules are benign—at least 95% of all detected pulmonary nodules are not cancer, most commonly representing old scars from infection (granulomas) or lymph nodes within the lung tissue 3

What You'll Experience

• Most people with pulmonary nodules have no symptoms at all—they are typically discovered incidentally on chest X-rays or CT scans done for other reasons 1

Types of Nodules

Based on Appearance

• Solid nodules: Completely white/opaque on CT scan 1
• Ground-glass nodules: Hazy appearance where you can still see blood vessels through them 1
• Part-solid nodules: A mix of both solid and ground-glass components 1

Based on Number

• Solitary nodule: A single nodule by itself 1, 2
• Dominant nodule with smaller nodules: One larger nodule with additional smaller spots—increasingly common and may be present in up to 50% of people getting thin-slice chest CT scans 1
• Multiple nodules: More than 10 nodules, which are usually caused by infections, inflammation, or cancer spread from elsewhere in the body rather than primary lung cancer 1

Risk of Cancer Based on Size

The smaller the nodule, the lower the cancer risk:

• Nodules less than 6 mm: Less than 1% chance of cancer 3
• Nodules 6-8 mm: 1-2% chance of cancer 3
• Nodules 8 mm or larger: Higher risk requiring formal risk assessment 4, 2

What Happens Next

Nodules That Don't Need Follow-up

You will not need any follow-up imaging or testing if your nodule has: 1, 4

• Certain patterns of calcium (diffuse, central, laminated, or "popcorn" pattern)
• Fat inside the nodule (indicates a benign tumor called hamartoma)
• Typical location and shape near the lung lining (perifissural or subpleural nodules that are smooth, triangular, and less than 10 mm)
• Size less than 5 mm

Nodules That Need Monitoring

For nodules 5-8 mm without worrisome features, your doctor will recommend repeat CT scans to watch for growth, typically at 6-12 months and again at 18-24 months, depending on your risk factors like smoking history 4, 2, 3

Nodules That Need Further Testing

For nodules 8 mm or larger, your doctor will calculate your cancer risk using validated prediction models (like the Brock model) that consider your age, smoking history, nodule size, shape, and location 4, 2

Based on this risk assessment: 4, 2

• Low risk (less than 10% chance of cancer): CT surveillance monitoring
• Intermediate risk (10-70% chance): PET-CT scan to further assess the nodule
• High risk (greater than 70% chance): Biopsy or surgical removal

Important Caveats

A nodule that has been stable (unchanged) for at least 2 years is almost certainly benign and typically requires no further follow-up 2, 3

Part-solid and ground-glass nodules require special attention because they have a higher association with a specific type of lung cancer (adenocarcinoma) but often grow very slowly, requiring longer surveillance periods 1, 4, 3

Even nodules with low uptake on PET scans or those that don't enhance with contrast can still be cancer, particularly certain types of adenocarcinoma, so a negative test doesn't completely rule out malignancy 4