18F-Fluorodeoxyglucose Positron Emission Tomography for the Diagnosis of Adrenocortical Tumors: A Prospective Study in 77 Operated Patients

CONTEXT: Most adrenal incidentalomas are nonfunctioning adrenocortical adenomas (ACAs). Adrenocortical carcinomas (ACCs) are rare but should be recognized at an early stage. OBJECTIVE: The objective of the study was to evaluate the usefulness of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) to predict malignancy in patients without a previous history of cancer. DESIGN: This was a prospective, multicenter study from 2001 to 2006. SETTING: The study was conducted at a network of seven university hospitals in Paris. PATIENTS: Seventy-seven patients were included. All underwent surgery because of hypersecretory and/or growing benign lesions (n = 18), obvious ACCs (n = 21), or radiologically indeterminate lesions (n = 38). MAIN OUTCOME MEASURE: The degree of (18)F-FDG PET uptake maximum standardized uptake value (maxSUV) was related to the pathological findings serving as a reference, and its diagnostic value was compared with that of computerized tomography (CT) scan. RESULTS: Pathology eventually diagnosed 43 ACAs, 22 ACCs, and 12 nonadrenocortical lesions. Using a cutoff value above 1.45 for adrenal to liver maxSUV ratio, the sensitivity and specificity to distinguish ACAs from ACCs were, respectively, 1.00 (95% confidence interval 0.85-1.00) and 0.88 (95% confidence interval 0.75-0.96). Among the 38 indeterminate lesions at CT scan, we could analyze a subgroup of 16 adrenocortical tumors with high unenhanced density (>10 HU) and an inappropriate washout: (18)F-FDG PET correctly predicted the benignity in 13 of 15 ACAs. CONCLUSIONS: In a multidisciplinary team approach, (18)F-FDG PET helps to manage suspicious CT scan lesions. An adrenal to liver maxSUV ratio less than 1.45 is highly predictive of a benign lesion.