Adrenal Washout Under Scrutiny: Spectrum, Pitfalls, and Mimics

Background Adrenal incidentalomas are frequently encountered on cross-sectional imaging, necessitating accurate non-invasive characterization to guide management. Computed tomography (CT) washout analysis is widely used to distinguish adenomas from non-adenomatous lesions; however, overlap in enhancement characteristics may lead to diagnostic pitfalls, particularly in hypervascular metastases. Methodology This retrospective case series includes six patients with incidentally detected adrenal lesions evaluated using a dedicated adrenal protocol on contrast-enhanced CT. Imaging assessment included unenhanced, portal venous, and delayed phase acquisitions, with calculation of the absolute percentage washout (APW). Lesions were characterized based on attenuation, morphology, and enhancement patterns, with correlation with clinical history and histopathological findings where available. Results Three lesions demonstrated classic features of lipid-rich adrenal adenomas, including low unenhanced attenuation and rapid washout (APW >60%). Two lesions represented adrenal metastases from biopsy-proven clear cell renal cell carcinoma (RCC), showing avid enhancement and high washout values (APW ~70%), thereby mimicking adenomas. However, these lesions demonstrated enhancement patterns concordant with the primary tumor, with additional metastatic disease in one case. One lesion represented adrenocortical carcinoma, characterized by large size, heterogeneity, necrosis, and intermediate washout. Conclusion CT washout analysis, while valuable, should not be interpreted in isolation. Hypervascular metastases, particularly from RCC, may demonstrate adenoma-like washout kinetics, representing an important diagnostic pitfall. Integration of imaging findings with clinical context and enhancement pattern analysis is essential for accurate lesion characterization and appropriate management.