Diagnostic importance of 18 F-FDG PET/CT parameters and total lesion glycolysis in differentiating between benign and malignant adrenal lesions Esra Ciftci, Bulent Turgut, Ali Cakmakcilar and Seyit A. Erturk Purpose Benign adrenal lesions are prevalent in oncologic imaging and make metastatic disease diagnoses difficult. This study evaluates the diagnostic importance of metabolic, volumetric, and metabolovolumetric parameters measured by fluorine-18-fluorodeoxyglucose ( 18 F-FDG) PET/CT in differentiating between benign and malignant adrenal lesions in cancer patients. Patients and methods In this retrospective study, we evaluated 18 F-FDG PET/CT parameters of adrenal lesions of follow-up cancer patients referred to our clinic between January 2012 and November 2016. The diagnosis of adrenal malignant lesions was made on the basis of interval growth or reduction after chemotherapy. Patient demographics, analysis of metabolic parameters such as maximum standard uptake value (SUV max ), tumor SUV max /liver SUV mean ratio (T/LR), morphologic parameters such as size, Hounsfield Units, and computed tomography (CT) volume, and metabolovolumetric parameters such as metabolic tumor volume and total lesion glycolysis (TLG) of adrenal lesions were calculated. PET/CT parameters were assessed using the Mann–Whitney U-test and receiving operating characteristic analysis. Results In total, 186 adrenal lesions in 163 cancer patients (108 men/54 women; mean ± SD age: 64 ± 10.9 years) were subjected to 18 F-FDG PET/CT for tumor evaluation. SUV max values (mean ± SD) were 2.8 ± 0.8 and 10.6 ± 6; TLG were 10.8 ± 9.2 and 124.4 ± 347.9; and T/LR were 1 ± 0.3 and 4.1 ± 2.6 in benign and malignant adrenal lesions, respectively. On the basis of the area under the curve, adrenal lesion SUV max and T/LR had similar highest diagnostic performance for predicting malignant lesions (area under the curve: 0.993 and 0.991, respectively, P < 0.001). Multivariate logistic regression analysis showed that T/LR, adrenal lesion SUV max , and Hounsfield Units were independent predictive factors for malignancy rather than TLG. Conclusion Irrespective of whether TLG was statistically highly significant for differentiating benign from malignant adrenal lesions, it did not reach the expected performance with a low negative predictive value. This may be because of the malignant but small and benign but large lesions on metabolovolumetric calculation. Nucl Med Commun 00:000–000 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. Nuclear Medicine Communications 2017, 00:000–000 Keywords: adrenal lesion, positron emission tomography/computed tomography, total lesion glycolysis Department of Nuclear Medicine, School of Medicine, Cumhuriyet University, Sivas, Turkey Correspondence to Esra Ciftci, MD, Department of Nuclear Medicine, School of Medicine, Cumhuriyet University, Sivas 58060, Turkey Tel: +90 506 382 6465; e-mail: esalkan@yahoo.com Received 8 March 2017 Revised 24 May 2017 Accepted 12 June 2017 Introduction Adrenal masses detected as incidentaloma in patients with no known malignancy are mostly benign [1]. In contrast, up to 50% of adrenal masses in patients with known extra- adrenal cancer are malignant [2]. Evaluation of cancer patients for staging or treatment response assessment with fluorine-18-fluorodeoxyglucose ( 18 F-FDG) PET/CT increases the frequency of adrenal mass detection. However, the accurate diagnosis of the lesion, whether benign or malignant, is challenging and PET/CT helps to avoid additional diagnostic procedures and aggressive treatment modalities. As biopsy is the gold standard for diagnosis, it is not always possible to apply this invasive procedure to oncologic patients in whom the prognosis will be altered by the biopsy [3]. The conventional criterion for the computed tomography (CT) diagnosis of adrenal adenoma is based on the CT attenuation value [Hounsfield Units (HU)]. A CT num- ber up to 10 HU from an unenhanced CT is diagnosed as lipid-rich adenomas [4]. However, hyperattenuating masses of more than 10 HU can be problematic in the differential diagnosis of lipid-poor adenoma and metas- tasis in cancer patients [5]. The accuracy of the adrenal protocol CT is almost 90–100% [5], but indeed this protocol consists of one unenhanced study and two-phase contrast-enhanced studies; also, there are disadvantages as patients are exposed to both an intravascular contrast injection as well as increased CT doses and radiation doses from con- ducting multiple CT-imaging diagnostics [4,6]. 18 F-FDG PET/CT is also valuable to differentiate benign adrenal from malignant lesions with a high sen- sitivity of 94–100% shown by visual assessment and/or Original article 0143-3636 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/MNM.0000000000000712 Copyright r 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.