Risk Stratification of Adrenal Masses by [18F]FDG PET/CT

Changing Tactics

Betty Salgues; Carole Guerin; Vincent Amodru; François Pattou; Laurent Brunaud; Jean-Christophe Lifante; Eric Mirallié; Nicolas Sahakian; Frédéric Castinetti; Anderson Loundou; Karine Baumstarck; Fréderic Sebag; David Taïeb


Clin Endocrinol. 2021;94(2):133-140. 

In This Article

Abstract and Introduction


Context: [18F]FDG PET/CT improves adrenal tumour characterization. However, there is still no consensus regarding the optimal imaging biomarkers of malignancy.

Objectives: To assess the performance of Tumour standardized uptake value (SUV)max:Liver SUVmax for malignancy-risk and to build and evaluate a prediction model.

Design/Methods: The cohort consisted of consecutive patients with adrenal masses evaluated by [18F]FDG PET/CT. The gold standard for malignancy was based on histology or a multidisciplinary consensus in nonoperated cases. The performance of the previously reported cut-off for Tumour SUVmax:Liver SUVmax (>1.5) was evaluated in this independent cohort. Additionally, a predictive model of malignancy was built from the training cohort (previous study) and evaluated in the validation cohort (current study).

Results: Sixty-four patients were evaluated; 28% of them had a Cushing's syndrome. Fifty-four adrenal masses were classified as benign and 10 as malignant (including 7 adrenocortical carcinomas). Compared to benign masses, malignant lesions were larger in size, had higher unenhanced densities and higher [18F]FDG uptake. CT-derived anthropometric parameters did not differ between benign and malignant masses. A tumour SUVmax:Liver SUVmax > 1.5 showed a good diagnostic performance: Se = 90.0%/Sp = 92.6%/PPV = 69.2%/NPV = 98.0% and accuracy = 92.2%. A predictive model based on tumour size and tumour-to-liver uptake SUVmax ratio for malignancy-risk was validated and provides a complementary approach to the ratio.

Conclusions: Tumour SUVmax:Liver SUVmax uptake ratio is a useful biomarker for diagnosis of adrenal masses. Another tactic would be to calculate with the model an individual risk of malignancy and integrate this information into a shared decision-making process.


The adrenal glands can be affected by a variety of pathologic conditions, including hyperplasia, haemorrhage, malignant (primary or secondary) and benign tumours from cortical or medullary origin. Tumours can be hyperfunctioning, when producing an increased amount of hormones, or nonhyperfunctioning, which are characterized by normal blood hormone levels. Therefore, in some cases, these lesions can be clinically suspected of malignancy, but in most cases, adrenal masses are discovered incidentally. Incidentalomas are typically found in approximately 5% of abdominal computed tomographies (CT) and are mainly benign in nature. Regardless of the mode of discovery, clinical history and physical examination, the first step relies on appropriate biochemical evaluation. Characterization of an adrenal mass by appropriate imaging investigations follows. In this setting, adrenal CT represents the first-level imaging modality for the evaluation of adrenal lesions. Several criteria have been defined on both imaging studies. High specificity for adrenocortical adenomas diagnosis was achieved using an unenhanced CT density cut-off of equal to or less than 10 Housfield units (HU).[1] Moreover, adrenocortical adenomas often exhibit a typical washout pattern, with an absolute enhancement washout of ≥60% and/or relative enhancement washout of ≥40% on contrast-enhanced CT[2,3] or demonstrate signal loss in opposed-phased magnetic resonance imaging (MRI).[4] MRI is not superior to CT, and among adrenal mass with unenhanced attenuation CT density > 30 HU, 66.6% remain indeterminate after chemical shift MRI.[5] Beyond these parameters, clinicians should be aware that tumour size is the best predictor of malignancy.[6,7] In frequent situations, the masses remain indeterminate on radiologic imaging or are too large for accurately ruling out malignancy risk, except for typical myelolipoma, cyst or haematoma.

Several studies have shown that the assessment of metabolic activity by 18F-fluorodeoxyglucose positron emission tomography-computed tomography ([18F]FDG-PET/CT) can help to characterize large and/or indeterminate masses. The use of tumour-to-liver uptake maximum standardized uptake values (SUVmax) ratio was found to more accurate than visual analysis in the distinction between benign and malignant tumours, with an optimal threshold varying across studies.[8,9] In a prospective study, we have previously shown that a ratio > 1.5 (from a receiver operating characteristic (ROC) curve) was associated with malignancy with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of 86.7%, 86.1%, 56.5%, 96.9% and 86.2%, respectively.[10] Although this cut-off value is useful, it is well known that some adrenocortical cancer and even large retroperitoneal sarcomas that may mimic adrenal tumours can exhibit lower uptake values.

Considering that tumour size and tumour-to-liver uptake SUVmax ratio represent predictors of malignancy, the primary goal of the study was to evaluate the performance of the previously reported tumour-to-liver uptake SUVmax ratio in a new independent cohort of 64 patients. The secondary goals were to built a probability model for predicting malignancy based on a previously reported cohort (87 patients) and validate the model in this new cohort that served as validation cohort. Finally, we also evaluated whether additional parameters such as CT-derived anthropometric parameters or contralateral adrenal gland morphology could add information.