Adrenal Washout Under Scrutiny: Spectrum, Pitfalls, and Mimics

Area of Science:

• Radiology
• Oncology
• Endocrinology

Background:

• Adrenal incidentalomas are common findings on cross-sectional imaging.
• Accurate non-invasive characterization is crucial for patient management.
• Computed tomography (CT) washout analysis is a key tool, but diagnostic pitfalls exist, particularly with hypervascular metastases.

Purpose of the Study:

• To evaluate the utility and limitations of CT washout analysis in characterizing incidentally detected adrenal lesions.
• To identify potential diagnostic pitfalls, specifically differentiating adrenal adenomas from hypervascular metastases.

Main Methods:

• Retrospective case series of six patients with incidentally detected adrenal lesions.
• Dedicated adrenal protocol on contrast-enhanced CT, including unenhanced, portal venous, and delayed phases.
• Calculation of absolute percentage washout (APW) and characterization based on attenuation, morphology, enhancement patterns, and clinical correlation.

Main Results:

• Three lesions were lipid-rich adrenal adenomas with low unenhanced attenuation and rapid washout (APW >60%).
• Two lesions were adrenal metastases from clear cell renal cell carcinoma (RCC), showing avid enhancement and high washout (APW ~70%), mimicking adenomas.
• One lesion was an adrenocortical carcinoma with intermediate washout, large size, heterogeneity, and necrosis.

Conclusions:

• CT washout analysis is valuable but should not be used in isolation.
• Hypervascular metastases, particularly from RCC, can exhibit adenoma-like washout kinetics, posing a diagnostic challenge.
• Integrating imaging findings with clinical context and enhancement pattern analysis is essential for accurate adrenal lesion characterization.