Certain malignant tumors show low metabolic activity including carcinoid and adenocarcinoma regardless of size (those with predominant ground-glass component, small solid components, and mucinous type). PET/CT is not a reliable test to distinguish benign from malignant ground-glass nodules (or part-solid nodules with small solid components). Because of the indolent behavior of ground-glass nodules, PET/CT sensitivity is low and follow-up chest CT is preferred [9,26-28]. Defective technique can also result in false-negative studies [4,41,42]. False-positive results on PET/CT also exist, mostly infectious and inflammatory lesions and less frequently sarcoidosis and rheumatoid nodules. Decreased FDG-PET/CT specificity to differentiate benign from malignant nodules has been recognized in regions with high prevalence of lung infections and reported as low as 25% in areas of endemic tuberculosis [40,43]. A meta-analysis of 70 studies showed FDG-PET/CT specificity adjusted for endemic infectious lung disease was 61% (95% CI, 49%-72%) compared to nonendemic regions 77% (95% CI, 73%-80%) [40,44]. Reyes et al [45] conducted a retrospective study comparing 351 biopsy-proven granulomatous and malignant nodules in a coccidioidal endemic region. Authors found that an elevated maximum standardized uptake value (SUVmax) was the only distinguishing feature between benign and malignant nodules. All nodules with SUVmax >5.9 were malignant, but there was overlap in nodules with SUVmax <5.9. Using an SUVmax <5.9, the sensitivity and specificity were 69% and 100%, respectively. This limitation should be recognized in endemic areas because it could alter the choice of next steps to more conservative options such as short-term follow-up CT. FDG-PET/MRI Whole Body There is no relevant literature to support the use of PET/MRI in the initial evaluation of incidentally detected pulmonary nodules. The use of FDG-PET/MRI in humans was first described in the early 2000s.
Incidentally Detected Indeterminate Pulmonary Nodule PCAs. Certain malignant tumors show low metabolic activity including carcinoid and adenocarcinoma regardless of size (those with predominant ground-glass component, small solid components, and mucinous type). PET/CT is not a reliable test to distinguish benign from malignant ground-glass nodules (or part-solid nodules with small solid components). Because of the indolent behavior of ground-glass nodules, PET/CT sensitivity is low and follow-up chest CT is preferred [9,26-28]. Defective technique can also result in false-negative studies [4,41,42]. False-positive results on PET/CT also exist, mostly infectious and inflammatory lesions and less frequently sarcoidosis and rheumatoid nodules. Decreased FDG-PET/CT specificity to differentiate benign from malignant nodules has been recognized in regions with high prevalence of lung infections and reported as low as 25% in areas of endemic tuberculosis [40,43]. A meta-analysis of 70 studies showed FDG-PET/CT specificity adjusted for endemic infectious lung disease was 61% (95% CI, 49%-72%) compared to nonendemic regions 77% (95% CI, 73%-80%) [40,44]. Reyes et al [45] conducted a retrospective study comparing 351 biopsy-proven granulomatous and malignant nodules in a coccidioidal endemic region. Authors found that an elevated maximum standardized uptake value (SUVmax) was the only distinguishing feature between benign and malignant nodules. All nodules with SUVmax >5.9 were malignant, but there was overlap in nodules with SUVmax <5.9. Using an SUVmax <5.9, the sensitivity and specificity were 69% and 100%, respectively. This limitation should be recognized in endemic areas because it could alter the choice of next steps to more conservative options such as short-term follow-up CT. FDG-PET/MRI Whole Body There is no relevant literature to support the use of PET/MRI in the initial evaluation of incidentally detected pulmonary nodules. The use of FDG-PET/MRI in humans was first described in the early 2000s.