Natural history of large adrenal tumors.

Objective: The aim of this study was to characterize large adrenal tumors (LATs), assess the diagnostic accuracy of imaging modalities in detecting malignant LATs, and determine whether further follow-up of seemingly benign LATs is necessary. Patients and methods: We retrospectively analyzed the clinical, biochemical, and imaging characteristics at presentation and during follow-up in a single-center cohort of patients with adrenal tumors ≥4 cm in diameter evaluated between June 2013 and June 2023. Results: Of 1,473 patients with adrenal tumors, 269 (18.3%) had lesions measuring ≥4 cm in diameter, of whom 220 were included in the study. Among LATs, 34.6% were adrenocortical adenomas, 27.3% other benign adrenal tumors, 17.3% adrenocortical carcinomas, 11.4% other malignant tumors, and 9.6% pheochromocytomas. Overall, 44.7% of tumors were non-functioning, while 37.8% secreted corticosteroids. Sensitivity of unenhanced computed tomography attenuation values in detecting malignancy was 100% using the threshold >10 Hounsfield units (HU) and 89.5% for >20 HU (with specificity 66.1% and 81.4%, respectively). Magnetic resonance with chemical shift analysis demonstrated high sensitivity (94.4%) but low specificity (56.8%). Conclusion: Although the risk of malignancy increases with tumor size, most LATs are benign. Imaging modalities demonstrate high sensitivity for detecting malignancy in LATs. No malignancies were identified in homogeneous lesions with attenuation <10 HU. LATs that do not meet these benign imaging criteria should undergo multidisciplinary evaluation and continued follow-up.