Pulmonary nodule: what the size and density on your CT mean

The words next to it

Words you may see beside pulmonary nodule on a report, and what each one changes.

Under 6 mm / 6 to 8 mm / over 8 mm

The size bands that the Fleischner follow-up rules use (the rules most reports cite). Between 3 and 10 mm, the size that counts is the average of the long and short measurements, rounded to the nearest millimeter, so 5 x 3 mm counts as 4 mm.

Part-solid / ground-glass (subsolid)

Hazier, less dense spots with rules of their own. They can be watched for up to 5 years, against about 2 for a solid one, and the ground-glass opacity page walks through them.

Calcified / fat-containing

Calcium or fat inside a nodule helps point to the cause. Certain calcium patterns (central, layered, popcorn or diffuse) or fat point to a harmless nodule, and some reports name the cause outright, as in a calcified granuloma.

Smooth vs spiculated / lobulated

Smooth edges usually point to a harmless cause. Spiky (spiculated) or bumpy (lobulated) edges are among the features doctors take more seriously.

Stable vs new / enlarging

Stable means unchanged from an older scan. New or enlarging means it changed, and on a screening CT growth means the average diameter rose by more than 1.5 mm in a year.

Lung-RADS 2 (or 1, 3, 4A, 4B)

You'll see this on a lung cancer screening CT, which uses its own system instead of the Fleischner rules below. A 1 or 2 means you're back for the usual yearly scan, though it doesn't rule out lung cancer.

How the Fleischner rules sort a solid nodule

The rules most reports point to come from the Fleischner Society. They weigh the nodule's size, its density and how many there are against your own risk, such as smoking or lung cancer in the family, and they're written for nodules found by chance in adults 35 and older.

Fleischner drew the 6 mm line at about a 1% lung cancer risk. Below it, a low-risk adult needs no routine scan. A higher-risk adult may be offered an optional CT at 12 months, more so if the nodule's shape looks suspicious or it sits in an upper lobe, as the one in the sample does.

At 6 to 8 mm, a CT at 6 to 12 months is usual. A second one at 18 to 24 months is considered for a low-risk adult and planned for a higher-risk one. Over 8 mm, doctors consider a CT at 3 months, a PET/CT or a biopsy.

Questions to ask the doctor

• Do you count me as low risk or high risk for this nodule, and why?
• I'm being treated for cancer. Who decides how this nodule is followed, and will my regular scans cover it?
• Is this the only nodule, or are there others you're following?
• If no follow-up scan is planned, what would make you want to look again?

Often on the same report

• Lung-RADS

  A 0 to 4 score used on lung cancer screening CT scans, based on the most concerning spot. 0 means incomplete. 1 (negative) and 2 (benign) count as a negative screen. 3 is probably benign. 4A, 4B, and 4X are suspicious and need a closer look.

• Ground-glass opacity

  A hazy area on the CT where the lung looks cloudier than normal, but the airways and blood vessels can still be seen through it. Many things can cause it, including infection, fluid, inflammation, scarring, and sometimes cancer.

• Spiculated

  The edges of the spot have a spiky, sunburst-like look. This pattern is highly suspicious for cancer, though infection or inflammation can also look this way.

• Calcified granuloma

  A small spot, usually in the lung, that has hardened with calcium. These most often form in response to an old infection that has healed, such as histoplasmosis or, rarely, TB.

• Perifissural nodule

  A small spot touching a fissure, the thin seam between lobes of the lung. When it has the typical look of a lymph node, with smooth edges, an oval, flat, or triangular shape, and a spot in the middle or lower lung, it's likely benign. Upper-lung spots or irregular edges get a closer look.

• Incidental finding

  Something the scan happened to show that wasn't what the test was looking for. Many have no bearing on health at all. Some are worth a closer look, and whether anything more is needed is the doctor's call.

Questions people ask

Are lung nodules common?

Very. Most are found by chance on a scan done for another reason, which is what "incidentally noted" means on a report.

What kind of infections cause lung nodules?

The most common harmless nodules are granulomas, small clusters of immune cells the body forms around an infection. Fungal lung infections and other infections such as tuberculosis can leave them behind.

Can you live a long life with lung nodules?

Usually, yes. Most small nodules aren't cancer, and a solid one that holds the same size through two years of follow-up isn't likely to be.

What is a solitary pulmonary nodule?

It means a single nodule, with no others seen on the scan. The follow-up rules treat one nodule and several differently.

Other phrases explained: Ground-glass opacity · Aortic atherosclerosis · Schmorl's node · Bone marrow edema