2017 Fleischner Society Guidelines — Reference Tables
Solid Nodules
| Size | Single — Low Risk | Single — High Risk | Multiple |
|---|---|---|---|
| <6 mm | No routine follow-up | Optional CT at 12 months | Low risk: No routine follow-up High risk: Optional CT at 12 months |
| 6–8 mm | CT at 6–12 months; consider CT at 18–24 months |
CT at 6–12 months; CT at 18–24 months |
CT at 3–6 months; consider CT at 18–24 months |
| >8 mm | CT at 3 months, PET/CT, or tissue sampling | CT at 3–6 months; CT at 18–24 months |
|
Subsolid Nodules — Pure Ground-Glass (GGO)
| Size | Single | Multiple |
|---|---|---|
| <6 mm | No routine follow-up | CT at 3–5 years |
| ≥6 mm | CT at 6–12 months to confirm persistence; if stable, CT every 2 years until 5 years | CT at 3–6 months; if stable, CT at 2 and 4 years |
Subsolid Nodules — Part-Solid
| Size | Single | Multiple |
|---|---|---|
| <6 mm | No routine follow-up | CT at 3–6 months; if stable, consider CT at 2 and 4 years |
| ≥6 mm | CT at 3–6 months to confirm persistence; if unchanged and solid component <6 mm, annual CT for 5 years | CT at 3–6 months; if stable, CT at 2 and 4 years |
How to Use This Calculator
This calculator applies the 2017 Fleischner Society guidelines to incidentally detected pulmonary nodules. Follow these steps to obtain a follow-up recommendation:
- Select nodule type — Choose solid, part-solid, or pure ground-glass (GGO) based on the CT appearance. If uncertain, see "Nodule Types Defined" below.
- Enter nodule size — Use the mean diameter (average of long-axis and short-axis measurements in the same plane). For multiple nodules, use the largest (dominant) nodule.
- Select nodule count — Choose single if there is one nodule, or multiple if two or more are present.
- Select patient risk (solid nodules only) — Indicate whether the patient has high-risk features such as smoking history, upper lobe location, family history of lung cancer, emphysema, or pulmonary fibrosis. Risk stratification does not alter management for subsolid nodules under the 2017 guidelines.
- Review the recommendation — The result panel shows the recommended follow-up interval with a color-coded urgency level and a follow-up timeline.
Important: Verify that the patient meets the Fleischner criteria applicability requirements before using this tool. The guidelines do not apply to patients under 35 years of age, immunocompromised patients, those with known primary malignancy, or lung cancer screening populations (use Lung-RADS instead).
About the Fleischner Society Guidelines
The 2017 Fleischner Society guidelines (MacMahon H et al., Radiology 2017;284:228–243) are the primary reference standard for managing incidental pulmonary nodules discovered on CT imaging. The Fleischner Society is an international thoracic radiology organization whose guidelines have been adopted by radiology, pulmonology, and thoracic surgery societies worldwide. The 2017 update replaced the 2005 guidelines, which were based on limited data and had a lower size threshold for recommending follow-up.
Pulmonary nodules are extremely common incidental findings on CT — studies suggest that up to 31% of individuals undergoing chest CT will have at least one nodule, with the vast majority being benign (infectious granulomas, intrapulmonary lymph nodes, or post-inflammatory scars). The central challenge is identifying the small subset of nodules that represent early-stage lung cancer, which is highly curable when detected incidentally and managed appropriately. The Fleischner guidelines provide an evidence-based framework that balances the harms of over-surveillance (radiation exposure, cost, patient anxiety) against the risk of missing a malignant nodule.
The 2017 revision incorporated several key advances: data showing that the malignancy risk for solid nodules under 6 mm is extremely low (under 1%), justifying the elimination of routine follow-up for this size category in low-risk patients; better characterization of subsolid nodule biology (GGO and part-solid lesions often represent indolent adenocarcinoma spectrum lesions requiring prolonged surveillance rather than urgent intervention); and the recognition that patient risk factors — particularly smoking history and upper lobe location — independently predict malignancy risk beyond nodule size alone.
- Raised the no-follow-up threshold for solid nodules from <4 mm to <6 mm in low-risk patients, reducing unnecessary follow-up CTs
- Incorporated subsolid nodule management (GGO and part-solid) as a separate track
- Stratified recommendations by patient risk factors, not just nodule size
- Addressed multiple nodules explicitly
- Recommended that the largest nodule guide management for multiple nodules
Interpretation Guide
Understanding the Color-Coded Urgency Levels
No Routine Follow-Up (green): The nodule has a very low malignancy risk based on current evidence. No CT surveillance is required. However, patients should be counseled about the incidental finding and advised to report new respiratory symptoms.
Optional Follow-Up (yellow): The recommendation is based on shared decision-making. An optional CT at 12 months is reasonable but not mandated. The clinician and patient should weigh the benefits of surveillance against radiation exposure and patient anxiety.
CT Follow-Up Required (amber): Scheduled CT surveillance is recommended to assess for interval growth. Growth of a nodule on follow-up CT — defined as an increase in mean diameter of 1.5 mm or more, or an increase in total nodule volume — is a key indicator of potential malignancy. Growth rate (volume doubling time) is an important secondary parameter.
Urgent Evaluation (red): The nodule size and/or morphology places it in a category where a definitive diagnostic strategy is needed promptly. Options include CT at 3 months (to assess growth), PET/CT (metabolic activity can distinguish benign from malignant), or tissue sampling (bronchoscopy or CT-guided biopsy). The appropriate choice depends on nodule morphology, patient surgical risk, and institutional expertise.
Part-Solid Nodule Special Considerations
Part-solid nodules deserve particular attention because the solid component — not the overall nodule size — drives clinical management. The solid component represents the invasive portion of adenocarcinoma spectrum lesions. A part-solid nodule that is stable in total size but shows growth of the solid component from 0 mm to 4 mm has undergone a clinically significant change and warrants escalation. The 2017 guidelines recommend that part-solid nodules with a solid component reaching or exceeding 6 mm be considered for resection, as this threshold correlates with invasive adenocarcinoma.
When Fleischner Criteria Do NOT Apply
The guidelines explicitly exclude the following populations — these patients require different management frameworks:
- Lung cancer screening programs — use Lung-RADS (ACR) instead
- Known malignancy — prior or active cancer changes management entirely
- Immunocompromised patients — higher infection risk changes differential
- Fever or infection — short-term follow-up to exclude infectious etiology first
- Patients <35 years — nodule prevalence and malignancy risk are different
Limitations & Considerations
The Fleischner 2017 guidelines are population-based recommendations derived from epidemiological studies and expert consensus. They carry inherent limitations that clinicians must factor into individualized patient management. Nodule size measurement variability between readers can be 1–2 mm, which is clinically significant near the 6 mm and 8 mm thresholds — if a nodule measures 6.0 mm on one read and 5.5 mm on another, the recommendation may change category. For borderline-sized nodules, the higher-risk management pathway is generally preferred.
The guidelines do not account for all morphological features that independently predict malignancy: nodule shape (spiculated margins carry a higher malignancy risk than smooth margins), density (calcified or fat-containing nodules are typically benign), and location (upper lobe nodules have higher malignancy rates than lower lobe). The calculator presented here uses the core size/type/risk framework; the radiologist's qualitative assessment of nodule morphology should supplement the size-based algorithm. Spiculated margins, upper lobe location, and new or growing nodules may warrant more aggressive management regardless of size.
PET/CT has limited sensitivity for nodules under 8 mm and for ground-glass nodules (which often have low metabolic activity even when malignant). Tissue sampling carries procedure-specific risks (pneumothorax for CT-guided biopsy, bleeding). These tradeoffs must be weighed against the benefit of definitive diagnosis. Multidisciplinary tumor board discussion is appropriate for any nodule where the management pathway is uncertain.
Nodule Types Defined
Solid nodule: Completely opaque on CT; does not allow visualization of underlying lung parenchyma. Most common type. Risk stratified by size and patient factors.
Pure ground-glass nodule (GGO): Hazy, increased attenuation but underlying lung structure still visible. No solid component. Often represents adenocarcinoma in situ (AIS) or minimally invasive adenocarcinoma (MIA). Typically very slow-growing.
Part-solid nodule: Mixed GGO with a solid component. The solid component is the most clinically concerning element — growth of the solid component (especially ≥6 mm) may warrant resection consideration.
High-Risk Factors
The 2017 guidelines define high-risk patients as those with any of the following:
- Current or former cigarette smoker (especially heavy smokers)
- Upper lobe nodule location
- Family history of lung cancer
- History of emphysema or pulmonary fibrosis on CT
- Occupational exposures (asbestos, silica, uranium, radon)
Low-risk patients are those with minimal or no smoking history and none of the above risk factors.
References
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. doi: 10.1148/radiol.2017161659
Callister ME, Baldwin DR, Akram AR, et al. British Thoracic Society guidelines for the investigation and management of pulmonary nodules. Thorax. 2015;70(Suppl 2):ii1–ii54.
Gould MK, Donington J, Lynch WR, et al. Evaluation of individuals with pulmonary nodules: when is it lung cancer? Diagnosis and management of lung cancer, 3rd ed. Chest. 2013;143(5 Suppl):e93S–e120S.