Fleischner Society Guidelines for Incidentally Detected Pulmonary Nodules on CT
The Fleischner Society guidelines are consensus recommendations for how to follow up small pulmonary nodules discovered incidentally on a CT scan done for some other reason. Rather than assigning a category, they suggest a follow-up direction — for example, no routine imaging, an optional or definite repeat CT at a suggested interval, or further workup — based on the nodule's type and size, whether there are one or several, and the patient's cancer risk. They are deliberately not a screening tool and not a categorical lexicon; the aim is to avoid unnecessary repeat scans for trivial nodules while ensuring meaningful ones are tracked. They pair naturally with Lung-RADS as the 'incidental versus screening' counterpart.
Combined the previously separate solid-nodule and subsolid-nodule guidance into a single, simplified set of recommendations, raised the minimum nodule size that triggers routine follow-up, expressed follow-up timing as ranges rather than fixed dates, and added guidance for multiple nodules.
Provided dedicated guidance for ground-glass and part-solid nodules, which the 2017 guideline later absorbed.
The original Fleischner guidance, limited to small solid nodules; superseded by the unified 2017 document.
Fleischner is a recommendation framework, not a category lexicon: it does not output a number or grade. Instead, the radiologist locates a nodule along several axes — its type (solid versus subsolid, with subsolid split into pure ground-glass and part-solid), its size, whether it is single or multiple, and the patient's risk level (low versus high) — and arrives at a suggested follow-up action. The precise size thresholds and recommended intervals should be read directly from the official 2017 Radiology paper.
These are our plain-language summaries. For the exact criteria, thresholds, and management rules, see the official source.
In a retrospective study of 740 CT/PET-CTs, three commercial AI lung nodule tools detected similar actionable nodules (p=0.73). However, small measurement variations led to significantly more BTS 1-year follow-ups for one tool (p<0.001 vs. another). Fleischner guidelines were mo…
Fleischner and Lung-RADS are complementary, not competing: Fleischner handles nodules found by chance on a non-screening CT, while Lung-RADS handles nodules found during organized low-dose CT lung-cancer screening of high-risk people. Fleischner is consensus guidance expressed as follow-up directions, whereas Lung-RADS is a categorical reporting system tied to screening programs. They use different size thresholds and decision logic, so the same nodule can yield different recommendations under each — they should not be substituted for one another. Fleischner also differs from disease-specific or screening guidelines from other bodies (e.g. NCCN, ACCP, BTS).
The 2017 guideline is the most widely cited reference for incidental pulmonary nodules and is broadly endorsed, with an educational companion clarifying its application. Real-world adherence, however, is imperfect: surveys show high awareness but inconsistent conformance when radiologists are tested on actual cases, and more recent data suggest radiologists self-report high adherence yet tend to overestimate how strong the underlying evidence base is. A 2026 comparison with Lung-RADS v2022 reinforced that, for identical solid nodules, the two systems diverge in follow-up timing and biopsy thresholds and are not interchangeable. The principal critiques are interobserver variability in nodule measurement/classification and the risk of both under- and over-follow-up when the guideline is applied loosely.
RadPigeon is an independent radiology news digest and is not affiliated with or endorsed by The Fleischner Society (independent thoracic-imaging society — NOT the ACR; not a 'RADS'). “Fleischner guidelines” is a trademark of its owner and is named here only to refer to the system. Always consult the official source for the exact, current criteria.
