Lung-RADS, or Lung CT Screening Reporting and Data System, is a standardized system developed by the American College of Radiology. Its primary purpose is to provide a clear and consistent way for radiologists to describe findings from low-dose computed tomography (CT) scans used for lung cancer screening. This system helps assess the likelihood of lung cancer based on imaging results.
The aim of Lung-RADS is to ensure medical professionals communicate effectively about screening outcomes, guiding appropriate follow-up actions for patients. By standardizing reports, it helps reduce confusion and ensures consistent care based on widely accepted guidelines.
Understanding the Lung-RADS Categories
The Lung-RADS system assigns a category from 0 to 4X to each low-dose CT lung screening exam, indicating the likelihood of lung cancer. These categories are based on the appearance, size, and growth of any nodules or other findings detected in the lungs.
Category 0: Incomplete
A Lung-RADS 0 designation means the CT scan is incomplete or additional information is needed to assign a definitive category. This can occur if a prior CT scan is unavailable, if parts of the lungs cannot be adequately evaluated, or if findings suggest an active infection or inflammation. In cases of suspected infection or inflammation, a follow-up low-dose CT scan is recommended within one to three months to re-evaluate findings once any acute process has resolved.
Categories 1 & 2: Negative Screen / Benign Appearance
A Lung-RADS 1 category indicates a negative screening result, meaning there are no nodules or only nodules with clearly benign features, such as specific calcification patterns or fat. The risk of lung cancer in this category is very low. A Lung-RADS 2 also indicates a benign appearance, where findings are present but highly unlikely to be cancerous. This might include solid nodules smaller than 6 millimeters that are stable, or non-solid (ground-glass) nodules under 30 millimeters. For both categories 1 and 2, continued annual low-dose CT screening is recommended.
Category 3: Probably Benign
A Lung-RADS 3 category suggests findings are probably benign, but with a low-to-moderate chance of malignancy. This category includes solid nodules at least 6 millimeters but smaller than 8 millimeters, or non-solid nodules 30 millimeters or larger. It can also include new or growing solid nodules smaller than 4 millimeters. A short-term follow-up low-dose CT scan, usually in six months, is recommended to monitor for changes.
Categories 4A, 4B, & 4X: Suspicious for Malignancy
Lung-RADS 4A indicates findings suspicious for malignancy, with a moderate probability of cancer. This category includes solid nodules 8 millimeters or larger, or part-solid nodules under 8 millimeters. A follow-up low-dose CT scan in three months or a positron emission tomography (PET/CT) scan might be considered to further assess findings.
Lung-RADS 4B signifies findings highly suspicious for malignancy, carrying a high probability of cancer. This includes larger solid nodules, part-solid nodules 8 millimeters or larger, or new or growing solid nodules 8 millimeters or larger. For this category, a PET/CT scan, biopsy, or surgical evaluation is often recommended to obtain a definitive diagnosis.
Lung-RADS 4X is a new addition for findings highly suspicious for malignancy, regardless of size, due to concerning features. This includes nodules with irregular shapes, spiculated margins, or those associated with atypical pulmonary cysts. The 4X designation prompts a biopsy or surgical assessment to further investigate the finding.
Key Updates in the 2022 Version
The 2022 version of Lung-RADS introduced several significant changes, refining classification and management recommendations. These updates incorporate new research and clinical experience to improve the accuracy and utility of the screening system.
One notable update is the introduction of the Lung-RADS 4X category, specifically for nodules exhibiting highly suspicious features, such as spiculated margins or irregular shapes, regardless of size. This new category ensures concerning findings trigger more immediate work-up, bypassing typical size-based thresholds for intervention.
The 2022 guidelines also adjusted criteria for a “positive” screening result, particularly impacting thresholds for certain nodule types. For instance, juxtapleural nodules, solid nodules located near the pleura, are now more broadly categorized as Lung-RADS 2 if smaller than 10 millimeters.
The updated guidelines offer new options for using previous non-screening CT scans for comparison. There are also new criteria for classifying and managing atypical pulmonary cysts. The system clarifies how cavitary nodules should be managed, generally treating them as solid nodules based on their total mean diameter.
Management and Follow-Up Recommendations
The Lung-RADS category assigned to a CT scan directly guides the recommended management and follow-up plan.
For a Lung-RADS 0 category, a follow-up low-dose CT scan is recommended within one to three months to resolve indeterminate findings, such as those related to infection or inflammation. Once clarified, a definitive Lung-RADS category can be assigned.
If a patient receives a Lung-RADS 1 or 2 category, indicating a negative or benign screen, the recommendation is to continue with annual low-dose CT lung cancer screening. These categories suggest a very low likelihood of cancer, and regular screening maintains surveillance for new developments.
For a Lung-RADS 3 category, which suggests probably benign findings, a short-term follow-up low-dose CT scan is advised in six months. This allows radiologists to monitor the nodule for growth or changes that might indicate a higher risk. If the nodule remains stable, the patient may return to annual screening.
When a Lung-RADS 4A is assigned, indicating suspicious findings with a moderate probability of cancer, further evaluation is warranted. This often involves a follow-up low-dose CT scan in three months, and a PET/CT scan may be considered to assess the nodule’s metabolic activity. For Lung-RADS 4B and 4X, which signify highly suspicious findings, more immediate diagnostic procedures are recommended. These include a PET/CT scan, a biopsy, or direct surgical assessment to definitively diagnose or rule out lung cancer.
Additional Modifiers and Considerations
Beyond the numerical categories, Lung-RADS reports can include additional modifiers to provide more comprehensive information about the CT scan findings.
The “S” modifier indicates other clinically significant findings on the CT scan not related to lung cancer. These might include abnormalities in other organs visible on the scan, such as significant coronary artery calcification, thyroid nodules, or issues with the aorta. While outside the scope of lung cancer screening, these findings can be important for a patient’s overall health and may require separate follow-up.
The “C” modifier is used when a patient has a documented history of lung cancer. A prior lung cancer diagnosis can change how new or existing lung nodules are interpreted and managed. Nodules in patients with a history of lung cancer may be treated differently, as they could represent a recurrence or a new primary lung cancer.