Characteristics of benign adrenocortical adenomas with 18F-FDG PET accumulation

Abstract

Introduction: Although 18F-FDG PET was originally developed to evaluate benign and malig nant tumors, the frequency of detection of benign adrenocortical adenomas showing FDG-PET accumulation has increased. However, the details of FDG-PET-accumulated benign adrenocortical adenomas have not been elucidated. Methods: To elucidate the pathophysiology of FDG-PET-positive cortisol- producing adrenal tumors, we performed clinicopathological and genetic analyses of adrenocortical adenomas examing FDG-PET in 30 operated patients with unilateral cortisol-producing adrenal tumors (26 adrenal adenomas and 4 adrenal cancers). Results: All adrenocortical carcinomas and 17/26 (65%) benign adrenocor tical adenomas showed high FDG accumulation (SUVmax ≥ 3). In adrenocortical adenomas with high FDG accumulation (SUV max ≥ 3), SUVmax showed a positive correlation with the CT Hounsfield units. A higher SU Vmax showed a clear black adenoma appearance with predominantly compact cells, which exhibited high T1 and T2 sig nals, a lack of signal drop on out-of-phase imaging on MRI, and less accumulation on 131-I adsterol scintigraphy. Furthermore, RNA-sequencing analysis revealed significant increases in the lysosomal and autophagy pathways and metabolic pathways, including glycolysis through glucose transporter (GLUT) 1 and 3, in black adenomas with high-level F DG accumulation. Discussion: A black adenoma is blackish due to lipofuscin, which accumulat es as a result of damaged mitochondria or proteins that escape lysosomal degradation or autophagy. Sin ce FDG in PET is taken up via GLUTs, alteration of the intracellular metabolic dynamics associated with mitochondrial damage in black adenomas may increase PET accumulation. Conclusion: Black adrenal adenomas should be considered with adrenal tumor s showing PET accumulation and low lipid contents.