Number of nodules
Caveats for using the Fleishner guidelines calculator for incidental pulmonary nodules:
- Applicable for patients ≥35 years old with incidental pulmonary nodules on CT imaging.
- Not to be used for
- Lung cancer screening
- For patients with known primary cancer
- Immunocompromised patients.
- Management depends on the most suspicious lung nodule.
- All CT scans of the thorax in adults should be reconstructed and archived with contiguous thin sections (≤1.5 mm, typically 1.0 mm) to accurately characterize and measure small pulmonary nodules. Multiplanar reformats in the sagittal and coronal planes are also recommended.
- Follow-up CT studies should be performed with a low dose protocol.
- For smaller nodules, dimensions are average of long and short axes, rounded to the nearest millimeter. Thus the size threshold (<6 mm) corresponds to a rounded measurement of 5 mm or less as per these guidelines.
- For nodules more than 10mm both long and short axes dimensions are documented.
- Volume thresholds of 100 and 250 mm3 are used for volumetry instead of the 6- and 8-mm thresholds used for linear measurements.
- Prior imaging studies should always be viewed to assess stability. Comparison from the earliest available study and most recent study should be performed.
- All attenuation measurements for nodules should be made on the thinnest available soft-tissue window images.
- Risk Factors for Malignancy
- Nodule Size and Morphology: Larger nodules and spiculated margins are worrisome.
- Nodule Location:
- Lung cancer – Upper lobes.
- Adenocarcinoma and Mets- Peripheral portions
- Squamous cancers – Near hila
- Perifissural solid nodules are usually benign intrapulmonary lymph nodes.
- Nodule Multiplicity: Multiplicity is associated with a lower risk of malignancy especially > 5.
- Nodule Growth Rate: Volume doubling time for cancers are in the range of 100–400-day range and correspond to an increase in diameter by 26%.
- Emphysema and Fibrosis: Increased risk.
- Age, Sex, Race, and Family History
- Tobacco and Other Inhaled Carcinogens
- Follow-up CT is NOT recommended when small nodules have a perifissural or other juxtapleural location and a morphology consistent with an intrapulmonary lymph node, even if the average dimension exceeds 6 mm.
- Recommendations for nodules detected on incomplete CT chest studies, for eg. Nodules at lung bases covered on CT abdomen:
- Most small nodules (<6 mm) – No further investigation
- Intermediate-size nodules (6–8-mm) nodules- Follow-up CT of the complete chest after an appropriate interval (3–12 months depending on clinical risk) to confirm stability and to evaluate additional findings.
- Large or very suspicious nodule – Complete dedicated CT thorax examination for further evaluation.
Fleischner Society 2017 Guidelines for Management of Incidentally Detected Pulmonary Nodules in Adults
Reference: Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017 Heber MacMahon et.al. Radiology 2017 284:1, 228-243. Read the complete article here: https://pubs.rsna.org/doi/10.1148/radiol.2017161659