Input Parameters
Optional. Without it, only relative washout can be calculated.
Portal venous phase, about 60–75 s after injection
15 minutes after injection
Calculated Washout
Absolute washout (APW)
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Relative washout (RPW)
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Result
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APW = (Enhanced − Delayed) / (Enhanced − Unenhanced) × 100
RPW = (Enhanced − Delayed) / Enhanced × 100
Interpretation
Enter the enhanced and delayed attenuation, and the unenhanced attenuation if available.
Thresholds and pitfalls
- Unenhanced 10 HU or less: lipid-rich adenoma; no washout needed.
- Absolute washout 60% or more (when unenhanced attenuation is available): consistent with adenoma.
- Relative washout 40% or more (when only enhanced and delayed phases are available): consistent with adenoma.
- Heterogeneous masses: washout cannot characterize masses with large areas of necrosis or hemorrhage. Size and growth on prior imaging still matter.
- Mimics: pheochromocytoma and hypervascular metastases (for example renal cell or hepatocellular carcinoma) can wash out in the adenoma range. Use clinical and biochemical context.
References
- Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology. 2002;222(3):629-633. doi:10.1148/radiol.2223010766
- Mayo-Smith WW, Song JH, Boland GL, et al. Management of incidental adrenal masses: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2017;14(8):1038-1044. doi:10.1016/j.jacr.2017.05.001
For education and as a reading aid; interpret with the full imaging and clinical picture.