From the Guidelines
For follow-up CT imaging of pulmonary nodules, a non-contrast CT scan is generally recommended. This approach is supported by the most recent and highest quality study, 1, which emphasizes that IV contrast is not required to identify, characterize, or determine stability of pulmonary nodules in clinical practice. The follow-up interval depends on the nodule characteristics and risk factors, typically ranging from 3-6 months for higher-risk nodules to 6-12 months for lower-risk nodules.
Key Considerations
- Non-contrast CT is the preferred method for pulmonary nodule surveillance as it provides adequate visualization of the nodules while minimizing radiation exposure and avoiding potential risks associated with contrast agents.
- The Fleischner Society guidelines recommend a follow-up CT at different time intervals, PET/CT, tissue sampling, or a combination depending on nodule size and attenuation, morphology, comorbidities, and other factors, as stated in 1.
- Certain nodule characteristics suggestive of benign etiology are better appreciated by CT and can avoid additional workup, such as diffuse, central, laminated, or popcorn calcifications patterns, as mentioned in 1.
Nodule Size and Follow-up
- For incidental indeterminate pulmonary nodules measuring <6 mm on chest CT, no follow-up is recommended given the low likelihood of malignancy, as stated in 1.
- For nodules >6 mm, a follow-up CT at different time intervals, PET/CT, tissue sampling, or a combination is recommended, depending on nodule size, attenuation, morphology, comorbidities, and other factors, as mentioned in 1.
Contrast-Enhanced CT
- Contrast-enhanced CT would only be indicated if there are specific concerns about vascularity, invasion of surrounding structures, or if the initial nodule appears suspicious for malignancy requiring better characterization, as stated in 1.
- The use of dynamic contrast-enhanced CT to quantify nodule enhancement and reflect vascularity is highly sensitive in detecting malignant nodules but is nonspecific, mainly due to active inflammatory and infectious nodules also showing high vascularity, as mentioned in 1.
From the Research
Follow-up Protocol for Pulmonary Nodules
The follow-up protocol for pulmonary nodules using computed tomography (CT) scan with or without contrast is as follows:
- For nodules < 4mm, a follow-up CT at 12 months is recommended in high-risk persons, whilst for low-risk persons no follow-up is needed 2.
- For solid, smooth or attached indeterminate nodules between 5 and 10mm, an annual repeat scan is recommended, whilst for purely intra-parenchymal nodules a 3-month repeat scan should be made to assess growth 2.
- The Lung-RADS guidelines recommend 3-month follow-up for category 4A nodules and downgrading to category 2 of all category 3 or 4 nodules that are unchanged for 3 months or longer, indicating benign behavior 3.
- However, studies have shown that malignant nodules can manifest growth slowly on follow-up CT, and 3-month follow-up CT has very low yield, suggesting that stability at 3-month follow-up should not instill high confidence in benignancy 3.
CT Scan Protocols
- The use of contrast-enhanced CT scans can help in the characterization of pulmonary nodules, but the timing of the scan delay can affect the volumetric measurements of the nodule 4.
- Studies have shown that contrast-enhanced volumes are significantly larger than unenhanced volumes, but the difference is not significant among volumes measured with different contrast-enhanced delays 4.
- The choice of CT scan protocol, with or without contrast, should be based on individual patient factors and the characteristics of the nodule 5, 6.
Nodule Size and Growth
- Nodule size and growth are important factors in determining the likelihood of malignancy 2, 3.
- Studies have shown that nodules with a volume doubling time of 400 days or less are more likely to be malignant 2.
- The measurement of nodule growth can be done using linear or volumetric measurements, and the definition of growth can vary depending on the type of nodule (solid, part-solid, or ground-glass) 3.