Note to first time users: this calculator can be used to check specific follow-up recommendations for incidentally detected, indeterminate pulmonary nodules. There is also an alternative volume-based formula if volumetric analysis can be performed. Please note that these recommendations do not apply to lung cancer screening, patients <35 years, or those with a prior history of primary cancer or immunosuppression.
Notes
This calculator is based on the 2017 updated version of the Fleischner Society guidelines for the management of incidental pulmonary nodules detected on CT but is neither official, nor endorsed by the aforementioned society.
Measuring nodules
- Nodules are typically measured in the axial plane, however since the 2017 version the sagittal/coronal plane can also be used if the greatest diameter can be measured in those planes.
- Always use the lung windows for measurements.
- Long and short axis diameters should be mesured on the same image.
- For 3-10 mm nodules the average of the short and long axis diameters should be used for assessment.
- <3 mm nodules should be uniformly termed micronodules.
- >10 mm nodules and masses should be described with both the short and long axis diameters in the report.
- For multiple nodules risk stratification/further diagnostic workup is defined by the largest or morphologically most suspicious one. It is an important disctinction, as the dominant nodule refers to the most suspicious one, which is not necessarily the largest.
- Part-solid nodules cannot be defined as such if at least 6 mm.
- Measurements should be rounded to the nearest whole millimeter.
- At least 2 mm nodule growth can be considered as significant.
- For larger nodules morphology becomes more easy to be appreciated, and should thus increasingly influence management rather than size alone.
- Volume doubling time (VDT) can be used as a further indicator of nodule behavior. This is best done using volumetric analysis. Radcalculators.org has VDT-calculators for volume-based (preferred method), or diameter-based VDT calculations.
- Special considerations apply to perifissural nodules. If the morphology (triangular or oval on axial images, and a flat or lentiform configuration in the sagittal or coronal plane) is characteristic for intrapulmonary lymph nodes no routine follow-up may be required even if they measure >6 mm.
Criteria for exclusion
- Patients ≦35 years – individualized management of incidentally encountered pulmonary nodules on a case-by-case basis is recommended instead.
- Cancer patients (including prior history of malignancy).
- Immunocompromised patients (increased risk of opportunistic lung infections).
- The setting of lung cancer screening – other systems designed specifically for this purpose, such as the Lung-RADS should be preferred.
Assessing risk category
- Risk assessment is partially depending on nodule features, but also on clinical information. Low risk is defined as <5% estimated cancer risk.
- Risk factors include:
- Older age
- History of smoking (however note the the recently increasing incidence of adenocarcinoma in nonsmokers)
- Family history of lung cancer
- Irregular or spiculated nodule margin
- Upper lobe location of the nodule
- Presence of emphysema or fibrosis
- Nodule multiplicity is less easily interepreted. In the NELSON trial increased lung cancer risk was found as nodule count increased from 1 to 4, but decreased in patients with >5 nodules.
Technical caveats
- The chest CT should be performed in full inspiration.
- Thin (<1.5 mm, ideally 1 mm) slice thickness is preferred, especially for measuring subcentimeter nodules.
- If a >8 mm nodule is identified incidentally on an incomplete scan (e.g. CT abdomen), instead of using the Fleischner recommendations, a complete chest CT should be performed as soon as possible.
- If volumetric analysis is performed, the follow-up imaging should be also assessed with the same software.
- The guidelines are not intended to preclude either shorter or longer term follow-up in individual subjects, when deemed clinically appropriate
For further informations it is recommended to read the Radiopaedia.org article and this excellent, illustrated summary by Radiology Assistant.
Last updated: 2021-09-05