Adrenal nodule PET/CT: Qualitative + quantitative eval—either/or or both?

Evaluation of adrenal nodules with F-18 FDG PET/CT was given a mean score of 93 percent diagnostic accuracy with an almost equally high percentage of interreader agreement, suggesting subjective visual interpretation is an effective method of evaluation, according to a review published July 4 in Academic Radiology.

Paul D. Evans, MD, from the department of radiology at Duke University Medical Center in Durham, N.C., evaluated studies involving F-18 FDG/PET imaging of adrenal nodules, either adenomas or metastases, and used both quantitative and qualitative methods to analyze the data.

“Excellent interreader agreement is seen for quantitative and qualitative methods of distinguishing benign from malignant adrenal nodules,” wrote Evans et al. “Qualitative analysis demonstrated higher accuracy but lower sensitivity compared with quantitative analysis.”

Researchers retrospectively reviewed 132 adrenal nodules in 105 patients who had undergone FDG PET/CT and were a mean age of 66 years with a history of lung cancer. Three readers evaluated each nodule independently and conducted two quantitative measurements using maximum standardized uptake value and standard uptake ratio with visual assessment as the qualitative measure. 

“Interreader agreement was calculated using percent agreement with k statistic for qualitative analysis and intraclass correlation coefficient (ICC) for quantitative analysis,” wrote the authors. “Accuracy, sensitivity, and specificity for distinguishing benign from malignant adrenal nodules were calculated for each method.”

Results showed interreader agreement for the visual and qualitative measure ranged from 92 to 96 percent with a k statistic of 0.79 to 0.90. For the quantitative measurements, ICC for maximum standardized uptake value was logged at 92 to 99 percent and ICC for standardized uptake ratio was determined to be 89 to 99 percent.

Mean sensitivity for diagnosing malignance using visual assessment was 80 percent and specificity 97 percent, whereas quantitative measurements were highly sensitive at 91 percent mean sensitivity for maximum standardized uptake value and 90 percent sensitivity for standardized uptake ratio. They were found to be less specific at 81 and 80 percent specificity, respectively, for maximum standardized uptake value and standardized uptake ratio.

“Our findings suggest that the qualitative method can be used as the primary method of adrenal nodule evaluation without compromising diagnostic accuracy, while quantitative methods of evaluation may provide confirmation and improved sensitivity in problematic cases,” the researchers wrote.

“Thus, qualitative assessment of adrenal nodules is in general acceptable (if not preferable), but since its sensitivity is slightly lower than quantitative methods, quantitative methods may be useful in problematic cases,” added Evans in an interview with Molecular Imaging Insight.