FDG-PET/CT characterization of adrenal nodules: Diagnostic accuracy and interreader agreement using quantitative and qualitative methods

Purpose: To determine interreader agreement and diagnostic accuracy across varying levels of reader experience using qualitative and quantitative methods of evaluating adrenal nodules using (¹⁸F)-fluorodeoxyglucose-positron emission tomography/computed tomography. Methods: 132 adrenal nodules (96 adenomas, 36 metastases) were retrospectively identified in 105 patients (49 men and 56 women, mean age 66 years, age range 45-85 years) with a history of lung cancer who underwent (¹⁸F)-fluorodeoxyglucose-positron emission tomography/computed tomography. For each nodule, three readers independently performed one qualitative and two quantitative measurements: visual assessment, standardized uptake value (SUV_max), and standard uptake ratio (SUV_ratio). Interreader agreement was calculated using percent agreement with κ statistic for qualitative analysis and intraclass correlation coefficient (ICC) for quantitative analysis. Accuracy, sensitivity, and specificity for distinguishing benign from malignant adrenal nodules were calculated for each method. Results: Percent agreement between readers for visual (qualitative) assessment was 92% to 96% and κ statistic was 0.79 to 0.90 (95%confidence limits 0.66-0.99). ICC for SUV_max was 92% to 99% (95% CL 0.8-1.0), and ICC for SUV_ratio was 89% to 99% (95% CL 0.74-0.99). For diagnosis of malignancy, mean sensitivity and specificity for visual assessment were 80% and 97%, respectively. Mean sensitivity and specificity for SUV_max were 91% and 81%, respectively; for SUV_ratio, 90% and 80%. Mean diagnostic accuracy was 93%, 83%, and 84% for visual assessment, SUV_max, and SUV_ratio, respectively. Conclusion: Excellent interreader agreement is seen for quantitative and qualitative methods of distinguishing benign from malignant adrenal nodules. Qualitative analysis demonstrated higher accuracy but lower sensitivity compared with quantitative analysis.