Fleischner Criteria — What It Means on Your Imaging Report
Quick Answer
The Fleischner Criteria are guidelines that tell doctors how to follow up on small lung nodules found on CT scans — most small nodules need only monitoring.
What Are the Fleischner Criteria?
The Fleischner Criteria are a set of evidence-based guidelines published by the Fleischner Society, an international group of thoracic radiology experts. These guidelines help doctors decide what to do when a small lung nodule shows up on a CT scan. The most recent update was published in 2017.
Finding a lung nodule on a CT scan is extremely common. Many people learn about a nodule through a routine chest CT, a lung cancer screening, or imaging done for an unrelated reason. The natural reaction is worry, but the Fleischner Criteria exist precisely because most small lung nodules are not cancer. They are often caused by old infections, lymph nodes, or scar tissue.
The guidelines take into account two main factors: the size of the nodule and your risk level. Risk level is based on things like whether you smoke or have smoked, your family history of lung cancer, and exposure to certain substances like asbestos or radon. By combining these two factors, the Fleischner Criteria help your doctor choose the right follow-up plan — avoiding unnecessary procedures for low-risk nodules while ensuring timely evaluation of those that need closer attention.
Categories / Classification
The 2017 Fleischner Society guidelines provide recommendations for incidental solid pulmonary nodules in adults (aged 35 and older). The table below summarizes the follow-up recommendations based on nodule size and patient risk profile.
| Nodule Size | Low-Risk Patient | High-Risk Patient |
|---|---|---|
| < 6 mm | No routine follow-up needed | Optional CT at 12 months |
| 6–8 mm | CT at 6–12 months | CT at 6–12 months, then consider CT at 18–24 months |
| > 8 mm | CT at 3 months, PET/CT, or tissue sampling | CT at 3 months, PET/CT, or tissue sampling |
What counts as low risk? Minimal or no smoking history and no other significant risk factors for lung cancer.
What counts as high risk? Smoking history (current or past), family history of lung cancer, exposure to asbestos, radon, or uranium, or upper-lobe nodule location.
These guidelines apply to solid nodules found incidentally (not through lung cancer screening programs, which follow separate protocols). Subsolid nodules (ground-glass or part-solid) have their own set of Fleischner recommendations with generally longer follow-up intervals because they tend to grow more slowly.
When You Might See This on Your Report
You will see references to the Fleischner Criteria on chest CT scan reports. Common scenarios include:
- A lung nodule found during a CT scan done for another reason, such as chest pain, shortness of breath, or a pre-surgical evaluation.
- A follow-up CT after a previous scan showed a nodule.
- An emergency room CT scan of the chest that incidentally reveals a small nodule.
Your radiologist may write something like "follow-up recommended per Fleischner Society guidelines" or reference the criteria directly. This is standard practice and indicates that your doctor has a clear, evidence-based roadmap for managing the finding.
Should I Be Worried?
For most people, the answer is no. Here is what each size category generally means for you.
Nodules smaller than 6 mm — These are very common and carry an extremely low risk of being cancer. The Fleischner Society determined that for low-risk patients, no routine follow-up is even necessary. If you have risk factors, your doctor may suggest a single follow-up CT at 12 months just to confirm the nodule has not changed.
Nodules between 6 and 8 mm — These are still small and most are benign. A follow-up CT at 6 to 12 months is recommended to check for growth. If you are at higher risk, your doctor may suggest an additional scan at 18 to 24 months. Stability over time is a strong indicator that a nodule is not cancerous.
Nodules larger than 8 mm — These deserve closer evaluation, which might include a follow-up CT at 3 months, a PET/CT scan to check metabolic activity, or in some cases a biopsy. A larger nodule does not automatically mean cancer, but your doctor wants to gather more information to make a confident assessment.
The key reassurance: the Fleischner Criteria are designed around the fact that the overwhelming majority of incidentally found lung nodules are benign. The guidelines exist to protect you — both from unnecessary procedures and from missing something that needs attention.
What Should I Do Next?
- Check your report for nodule size and follow-up recommendations. The size measurement and any mention of Fleischner guidelines will tell you and your doctor the next step.
- Talk to your doctor about your risk factors. Be honest about smoking history, family history of lung cancer, and occupational exposures. This helps your doctor determine whether you fall into the low-risk or high-risk category.
- Schedule any recommended follow-up imaging on time. If your report says to repeat a CT in 6 or 12 months, mark it on your calendar. Timely follow-up is the most important thing you can do.
- Bring prior imaging to your appointments. Comparing a nodule across multiple scans is one of the best ways to assess whether it is stable or growing. Keep records of past CT scans.
- Ask your doctor to explain your specific situation. For guidance on having productive conversations about your imaging results, see our article on how to discuss imaging results with your doctor.