Fleischner Criteria – Fleischner Society 2017 Guidelines: Updated Follow-Up for Incidental Pulmonary Nodules [Classics Series]

The following study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Radiology: Summaries of Clinically Relevant & Recent Landmark Studies, 1e (The Classics Series).

1. The 2017 update to the Fleischner Society Guidelines greatly reduces unnecessary follow-up imaging for incidental solid and subsolid pulmonary nodules by increasing the size threshold for routine surveillance and using follow-up time ranges rather than rigid intervals. 

2. In low-risk adults, incidentally detected nodules under 6 mm (both solid and ground-glass or part-solid) generally do not require follow-up; higher-risk individuals may warrant a single CT at 12 months. Nodules of 6 mm or larger demand follow-up tailored by type, size, and risk factors.

4. Risk factors for malignancy include nodule size, tobacco and other known carcinogens, family history, upper lobe location, emphysema, and pulmonary fibrosis.

 Original Date of Publication: March 2017 

Study Rundown: The Fleischner Society’s 2017 guidelines, published in Radiology, represent a major update to the organization’s prior recommendations for managing incidentally detected pulmonary nodules. These changes consolidated the 2005 solid nodule guidelines and the 2013 subsolid nodule guidelines into a single, streamlined framework designed to reduce unnecessary imaging and associated patient anxiety, cost, and radiation exposure.

One of the most important changes was raising the minimum size threshold for routine follow-up from 4 mm to 6 mm. This shift was supported by data from large international lung cancer screening trials showing that nodules under 6 mm in low-risk patients carry a <1% malignancy risk, even in populations with higher baseline risk. By avoiding follow-up in these very low-risk cases, clinicians can focus resources on patients more likely to benefit from surveillance.

For low-risk patients with solid or subsolid nodules smaller than 6 mm, no follow-up is generally recommended. In high-risk patients, an optional CT scan at 12 months may be considered. Solid nodules between 6–8 mm typically require one follow-up CT at 6–12 months, with a second scan at 18–24 months for selected cases. Nodules larger than 8 mm warrant more definitive evaluation, which may include an early CT at 3 months, PET-CT, or tissue sampling depending on risk factors and imaging features.

Subsolid nodules—including pure ground-glass and part-solid nodules—have unique growth patterns and a higher likelihood of representing indolent adenocarcinomas. For these, the guidelines recommend follow-up at 6–12 months and then periodic surveillance for up to 5 years. This extended timeframe reflects the slow progression of many subsolid lesions and helps avoid premature invasive testing.

The 2017 update also moved away from rigid follow-up timelines, introducing time ranges that give clinicians the flexibility to personalize surveillance based on the patient’s overall risk profile, nodule morphology, and comorbidities. For accurate characterization, the guidelines emphasize the use of thin-section CT imaging (≤ 1.5 mm slice thickness) with coronal and sagittal reconstructions.

When multiple nodules are present, management is based on the most suspicious nodule rather than applying recommendations to each lesion individually. This prevents over-surveillance while ensuring that the highest-risk findings receive appropriate attention.

Overall, the 2017 Fleischner Society Guidelines mark a shift toward risk-stratified, evidence-based management of incidental pulmonary nodules, minimizing unnecessary follow-up for small, low-risk lesions while ensuring timely investigation of those more likely to represent lung cancer.

Click to read the study in Radiology

MacMahon H, Naidich DP, Goo JM, Lee KS, Leung AN, Mayo JR, Mehta AC, Ohno Y, Powell CA, Prokop M, Rubin GD. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology. 2017 Feb 23:161659.

 Additional Review:

Pinsky PF, Gierada DS, Black W, Munden R, Nath H, Aberle D, et al. Performance of Lung-RADS in the National Lung Screening Trial A Retrospective Assessment Performance of Lung-RADS in the NLST. Ann Intern Med. 2015 Apr 7;162(7):485–91.

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