Adrenal Lesion SUV on PET-CT

The SUV_max for each adrenal nodule was recorded by drawing a rectangular three-dimensional region of interest around the nodule. Verification that the location of the demarcated SUV_max pixel resided within the adrenal nodule was performed by viewing the fused images. The rectangular region of interest was adjusted to exclude adjacent FDG-avid structures.

The average liver SUV (SUV average) for each patient was recorded by drawing a 90-cm³ rectangular three-dimensional region of interest centered within the right hepatic lobe. Care was taken to exclude any abnormalities, portions of the gallbladder, and the fissure of the ligamentum teres. The liver SUV average could not be measured in one patient because of extensive intrahepatic metastases. The adrenal SUV_max was divided by the liver SUV average to calculate a ratio (SUV ratio) for each nodule.

Conclusion: Definitive identification of many metastases can be accomplished by applying an SUV ratio cutoff of greater than 2.5, allowing pragmatic management of adrenal nodules that initially test positive with the combined PET/CT criteria SUV_max > 3.1 and mean attenuation > 10 HU.

• We found that recent proposed thresholds of nodule maximum standardized uptake value (SUV_max) greater than 3.1 and nodule SUV ratio (ratio of nodule SUV_max to liver SUV average) greater than 1.0 had the same sensitivity; however, the SUV_max threshold was more specific and yielded fewer false-positive results.
  
• Combined PET/CT has improved accuracy compared with PET alone when using a mean attenuation threshold of greater than 10 HU; however, lipid-poor fluorine 18 fluorodeoxyglucose (FDG)-avid adrenal adenomas lead to a high number of false-positive findings.
  
• Further application of a high SUV ratio threshold of greater than 2.5 separated many true-positive metastases from false-positive FDG-avid adrenal adenomas.

• The proposed algorithm refines the evaluation of adrenal nodules with PET/CT when staging disease in patients known to have or suspected of having lung cancer.
  
• The proposed algorithm allowed definitive characterization of 72 (76%) of 95 adrenal nodules found at PET/CT and can therefore spare some patients from undergoing further imaging or interventions.

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Adrenal Nodules at FDG PET/CT in Patients Known to Have or Suspected of Having Lung Cancer: A Proposal for an Efficient Diagnostic Algorithm¹

Matthew J. Brady, MD, John Thomas, MBBS, Terence Z. Wong, MD, Kendra M. Franklin, MD, Lisa M. Ho, MD, and Erik K. Paulson, MD

¹ From the Department of Radiology, Duke University Medical Center, Erwin Rd, Durham, NC 27710. From the 2007 RSNA Annual Meeting. Received February 1, 2008; revision requested April 2; revision received June 17; accepted July 1; final version accepted August 29. Address correspondence to M.J.B., Roper Radiologists, PA, 316 Calhoun St, Charleston, SC 29401.