What the 2017 guidelines changed
The 2017 revision raised the size threshold below which no routine follow-up is needed from 4 mm to 6 mm, replaced fixed intervals with ranges to allow clinical judgement, and reduced the number of recommended follow-up examinations. It also stopped separating nodules by exact millimetre bands in favour of three broad groups.
The guidelines apply to incidentally detected nodules in patients aged 35 and over. They do not apply to lung cancer screening — that is Lung-RADS — nor to patients with known primary cancer or immunosuppression, where a nodule carries a different prior probability entirely.
Solid nodules
Size is measured as the average of long and short axis on the same image, and the bands are under 6 mm, 6 to 8 mm, and over 8 mm. Patient risk changes the recommendation only in the smallest band and in the single-nodule 6 to 8 mm band.
High risk means a heavy smoking history, older age, upper lobe location, spiculated margin, emphysema or fibrosis, or a family history. It is a composite judgement, not a score.
| Size | Single, low risk | Single, high risk | Multiple |
|---|---|---|---|
| < 6 mm | No routine follow-up | Optional CT at 12 months | No routine follow-up (low risk) |
| 6–8 mm | CT at 6–12 months, then consider 18–24 months | CT at 6–12 months, then CT at 18–24 months | CT at 3–6 months, then consider 18–24 months |
| > 8 mm | Consider CT at 3 months, PET/CT or tissue sampling | Consider CT at 3 months, PET/CT or tissue sampling | CT at 3–6 months, then consider 18–24 months |
Subsolid nodules
Subsolid nodules are divided into pure ground-glass and part-solid, and the two behave very differently. A pure ground-glass nodule grows slowly and is followed over years; a part-solid nodule is judged on the size of its solid component, because that component is what carries the invasive risk.
For part-solid nodules 6 mm or larger, a solid component of 6 mm or more is the point at which the lesion is treated as suspicious rather than followed. Below that, persistence is confirmed first.
Any subsolid nodule needs to be shown to persist before a long follow-up schedule is started — a proportion resolve, and a transient inflammatory focus does not deserve five years of surveillance.
| Type | Size | Recommendation |
|---|---|---|
| Pure ground-glass, single | < 6 mm | No routine follow-up |
| Pure ground-glass, single | ≥ 6 mm | CT at 6–12 months to confirm persistence, then CT every 2 years until 5 years |
| Pure ground-glass, multiple | < 6 mm | CT at 3–6 months; if stable, consider CT at 2 and 4 years |
| Part-solid, single | < 6 mm | No routine follow-up |
| Part-solid, single | ≥ 6 mm | CT at 3–6 months to confirm persistence; then judged on the solid component |
Where Fleischner is most often misapplied
It is used for a screening population. Fleischner is for incidental nodules. A patient in a lung cancer screening programme is managed under Lung-RADS, which has different thresholds and a different follow-up structure.
It is used in a patient with known malignancy. A nodule in that setting is a potential metastasis and sits outside these guidelines entirely.
Multiple nodules are managed by the largest. The recommendation follows the most suspicious nodule, which may not be the biggest one.
The solid component of a part-solid nodule is not measured separately. The total diameter and the solid component are different numbers and the guideline turns on the second.
It is applied under age 35. Below that, the prior probability of malignancy is low enough that the guideline does not apply and a shorter, individualised approach is preferred.
Frequently asked questions
What are the Fleischner Society guidelines?
Consensus recommendations for how to follow up a pulmonary nodule found incidentally on CT. The current version was published in 2017 and covers solid, pure ground-glass and part-solid nodules in patients aged 35 and over.
What size pulmonary nodule needs follow-up?
Under the 2017 guidelines, a solid nodule smaller than 6 mm in a low-risk patient needs no routine follow-up. At 6 mm the threshold for follow-up is crossed. In a high-risk patient a nodule under 6 mm may optionally be re-imaged at 12 months.
How is a pulmonary nodule measured for Fleischner?
As the average of the long and short axis measured on the same transverse image, rounded to the nearest millimetre. For part-solid nodules the solid component is measured separately, because the recommendation depends on it.
What counts as a high-risk patient?
A heavy smoking history, older age, upper lobe location, spiculated margin, emphysema or pulmonary fibrosis, or a family history of lung cancer. It is a composite clinical judgement rather than a calculated score.
Do the Fleischner guidelines apply to lung cancer screening?
No. Screening-detected nodules are managed under Lung-RADS, which uses different size thresholds and a different follow-up structure. Fleischner applies to nodules found incidentally on a scan performed for another reason.
How are multiple pulmonary nodules handled?
Management follows the most suspicious nodule rather than the largest, and follow-up intervals are generally shorter than for a single nodule of the same size.
Why do part-solid nodules have their own rule?
Because the solid component is what carries the risk of invasive disease. A 10 mm part-solid nodule with a 2 mm solid component and one with an 8 mm solid component are managed very differently, so the total diameter alone is not enough.
Does this calculator send anything anywhere?
No. It runs entirely in your browser, makes no network requests, stores nothing and has no analytics. It works offline and from a USB stick on a reporting workstation.
Source
MacMahon H, Naidich DP, Goo JM, et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology. 2017;284(1):228-243.
This tool is an independent implementation and is not affiliated with or endorsed by the American College of Radiology or any other body named here. It is intended for qualified healthcare professionals, and it supports a reporting decision rather than making one. The published guideline remains normative.