Clinical and Radiological Features of Atypical Adrenal Masses - A Multicenter Retrospective Study

Context: The natural history and malignant potential of cases classified as atypical adrenal masses (AAMs) are unknown. Objective: To describe the radiological characteristics and clinical outcomes of AAMs. Design and Participants: A multicenter retrospective study. Patients ≥18 years old with AAMs [diameter of 10-39 mm on first imaging study and pre-contrast attenuation of >10 Hounsfield units (HU) on computed tomography] were studied. We excluded adrenal metastasis, pheochromocytoma, sarcoma, lymphoma, infiltrative lesions, and adrenal hemorrhage, as well as patients with genetic predisposition to adrenal neoplasms. Data are presented as percentages and median values with interquartile ranges (IQRs). Results: We included 217 patients with 224 adrenal masses (61.3% women); the median age was 58 years (IQR 49-65 years). The median size was 20.5 mm (IQR 15-27 mm), with a median precontrast attenuation of 23.5 HU (IQR 17-30 HU). The median AAM growth rate was 0.3 mm/year (IQR 0-1.8 mm/year). Seventy-one masses (31.7%) underwent pathological evaluation. Adrenal adenoma (n = 38; 17%) and adrenocortical carcinoma (ACC) (n = 25; 11.2%) were the 2 most common diagnoses. For the adenomas, the growth rate was 0.3 mm/year (IQR 0-2.3 mm/year) and for ACCs, the growth rate was 12.9 mm/year (IQR 3.5-22 mm/year). The absolute contrast washout was >60% in 5 out of 7 (71.4%) ACC cases. The best growth rate cutoff for predicting malignancy was 2.68 mm/year (area under the curve 0.939; sensitivity 87.5%, specificity 88.8%). Conclusion: AAMs carry significant malignant potential, and long-term follow-up is warranted when surgery is not pursued. Contrast washout is not reliable in predicting malignant potential of AAMs.