lung rads basics

A solid 4-mm nodule identified on the initial screening LDCT scan is a Lung-RADS category 2 finding. Lung nodules in the Lung CT Screening Reporting & Data System (Lung-RADS) category 2 are thought to have a very low risk of malignancy (<1%). The management recommendation is to return to annual screening (choice B is correct). Lung cancer screening with LDCT is standard of care for those at high risk based on age and smoking history criteria. Lung cancer screening is thought to have more benefit (lung cancer mortality reduction) than harms when conducted in a high-quality program. The most significant harms come from the management of screen-detected findings, particularly lung nodules. Lung nodules are frequently identified on LDCT scans. The frequency reported depends on the definition of a positive finding. Different lung nodule size thresholds and growth rates have been used in screening studies to define a positive finding. Unfiltered, lung nodules may be found in 50% to 90% of all screening LDCT scans. In the National Lung Screening Trial (NLST), a positive finding was defined as a lung nodule 4 mm or larger in diameter. This definition led to a positive result in 27% of baseline screens and 39% after two additional annual screening rounds. In the Dutch Belgian Lung Cancer Screening Trial (NELSON) study, where a positive finding was defined as a nodule volume of 500 mm3 or larger, or between 50 and 500 mm3 with a volume doubling time <400 days as determined with LDCT performed 3 months after the initial one, only 2.3% were positive on the baseline scan. Screening-detected lung nodules are managed much as incidentally detected lung nodules, with an assessment of the risk of malignancy on the basis of the clinical risk factors of the individual and the imaging features of the nodule. Differences of note are that all individuals screened are at high risk by definition of their eligibility and that screening occurs annually, providing an opportunity for built-in surveillance of very low-risk nodules.

To standardize management of screening-detected nodules, with the goal of mitigating the frequency with which additional imaging is performed for their evaluation, the American College of Radiology developed the Lung-RADS reporting and management system. The Lung-RADS system assigns a category to the exam on the basis of the risk of the most concerning lung nodule. Category 1 is assigned when there are no nodules identified on imaging. The next LDCT recommended is the annual scan. Category 2 is assigned when the largest nodule has a very low risk of malignancy (1% or less; solid nodules <6 mm in diameter on the initial scan). The next LDCT recommended is the annual scan. Category 3 is assigned when the largest nodule has a low risk of malignancy (1%-2%; solid nodules 6 to <8 mm in diameter on the initial scan). The next LDCT recommended is 6 months later. Category 4 is assigned when the largest nodule has at least a moderate risk of malignancy (≥8 mm; 5%-15% for category 4A and >15% for category 4B). The evaluation may include follow-up CT in 3 months, PET/CT scanning, or nonsurgical biopsy or surgical resection, on the basis of the probability of malignancy and the clinical characteristics of the individual. Use of the Lung-RADS system highlights trade-offs in nodule management and the importance of high-quality screening. By increasing the size threshold of a nodule that would require additional testing prior to the annual scan from that used in the NLST (ie, from 4 to 6 mm), far fewer nodules require additional testing (increased specificity), while the diagnosis of a portion of the smallest cancers may be delayed (decreased sensitivity). The effect of this delay is magnified by poor compliance with annual follow-up, which has been an issue for screening, particularly when abnormal findings are not identified on the prior scan. Even the smallest nodules, those <4 mm in diameter in the NLST, represented 1.2% of the lung cancers detected in the study. The patient in this question was compliant with her annual screening exam. The annual scan showed a substantial increase in the size of the previously identified nodule and the development of a large level 4R lymph node (Figure 2 and Figure 3). Bronchoscopic biopsy and additional staging identified a limited stage small cell lung cancer.