From the Guidelines
For incidental indeterminate pulmonary nodules measuring less than 6 mm on chest CT, the Fleischner Society guidelines do not recommend routine follow-up given the likelihood of malignancy is less than 1%. According to the guidelines, exceptions are made for nodules with suspicious imaging features that increase the malignancy risk to the 1% to 5% range, in which case a follow-up chest CT may be appropriate at different time intervals, based on nodule attenuation, after considering a patient’s preferences and comorbidities 1.
Key Considerations
- The guidelines emphasize the importance of image quality in evaluating pulmonary nodules, with factors such as thinner CT sections, nodule location and size, and nodule attenuation affecting detection sensitivity 1.
- For follow-up CTs, the use of contiguous thin sections (1.5 mm) and reconstructed multiplanar images is recommended to ensure adequate characterization, particularly for nodules with a ground-glass attenuation component 1.
- Low-dose technique is recommended for CTs performed to follow lung nodules, and standardization of acquisition and reconstruction CT protocols can help reduce errors in measuring nodule size, attenuation, and volume 1.
- IV contrast is not required to identify, characterize, or determine stability of pulmonary nodules in clinical practice, which is also supported in lung cancer screening 1.
Imaging Recommendations
- For incidental indeterminate pulmonary nodules less than 6 mm on chest CT, a next imaging study of CT Chest Without IV Contrast is recommended 1.
- The mean attenuation value of indeterminate benign and malignant nodules on unenhanced CT is not significantly different, and therefore not useful in their differentiation, but multiple imaging features can increase the risk of malignancy, including nodule size, morphology, location, multiplicity, or the presence of emphysema or fibrosis 1.
From the Research
Fleischer Society Guidelines
The Fleischer Society guidelines for the management of small pulmonary nodules detected on CT scans were published in 2005 2. The guidelines propose the following management strategies:
- Small solid nodules (<8 mm) can be followed with a repeat chest CT in 6 to 12 months, depending on the presence of patient risk factors and imaging characteristics associated with lung malignancy.
- Larger solid nodules (≥8 mm) require further evaluation, including surveillance imaging, positron emission tomography-CT imaging, nonsurgical biopsy, or surgical resection.
- Subsolid nodules, including ground-glass nodules and part-solid nodules, are managed based on their size and the size of the solid component.
Key Recommendations
The guidelines emphasize the importance of considering the probability of malignancy, patient comorbidities, and patient preferences when managing pulmonary nodules. The following key points are highlighted:
- The probability of malignancy is less than 1% for nodules smaller than 6 mm and 1% to 2% for nodules 6 mm to 8 mm.
- Nodules that are 6 mm to 8 mm can be followed with a repeat chest CT in 6 to 12 months.
- Part-solid pulmonary nodules are managed according to the size of the solid component, with larger solid components associated with a higher risk of malignancy.
- Ground-glass pulmonary nodules have a probability of malignancy of 10% to 50% when they persist beyond 3 months and are larger than 10 mm in diameter.
Rationale and Evidence
The guidelines are based on the analysis of various studies, including the NELSON trial 3, which used distinctions based on nodule volumetric assessment and growth rate to manage lung nodules detected on low-dose CT screening. Other studies, such as the National Lung Screening Trial (NLST) 4, have also provided evidence on the long-term cancer risk associated with lung nodules observed on low-dose screening CT scans. The guidelines aim to optimize lung nodule management in screening programs and provide a comprehensive overview of outcomes specific to lung cancer screening 3, 5.