Calculators · Adrenal CT · ACR 2017
Adrenal washout calculator: absolute and relative
Absolute washout is 100 × (portal venous − delayed) ÷ (portal venous − unenhanced), and relative washout is 100 × (portal venous − delayed) ÷ portal venous. By ACR 2017, absolute ≥ 60% or relative ≥ 40% is consistent with adenoma, and unenhanced attenuation ≤ 10 HU indicates a lipid-rich adenoma, with no need for washout.
Example
- Absolute washout
- 67.7%
- Relative washout
- 52.5%
Absolute washout of 67.7% (≥ 60%): consistent with adenoma.
Report lineAdrenal nodule measuring 2.2 cm, with unenhanced attenuation of 18 HU, 80 HU in the portal venous phase, 38 HU in the delayed phase (15 min), absolute washout of 67.7% and relative washout of 52.5%.
Calculation support for physicians. The result does not replace the assessment of the exam or the decision of whoever signs the report. Page published on .
Formula
Absolute washout = 100 × (portal venous − delayed) ÷ (portal venous − unenhanced)
Relative washout = 100 × (portal venous − delayed) ÷ portal venous
Thresholds
| Measurement | Threshold | Reading |
|---|---|---|
| Unenhanced attenuation | ≤ 10 HU | Lipid-rich adenoma. Washout is not needed. |
| Absolute washout | ≥ 60% | Consistent with adenoma. |
| Relative washout | ≥ 40% | Consistent with adenoma, when there is no unenhanced phase. |
| Below the thresholds | < 60% and < 40% | Indeterminate on CT. |
What to look for
- Valid with a 15-minute delayed phase and an ROI covering about half to two-thirds of the lesion, without necrosis or hemorrhage.
- Hypervascular metastasis (such as renal cell or hepatocellular carcinoma) and pheochromocytoma can have high washout; interpret with the clinical picture.
- Indeterminate: follow the ACR flowchart according to size, oncologic history and prior exam. Chemical-shift MRI, comparison with prior imaging, PET/CT or biopsy can clarify.
- Lesion ≥ 4 cm: the ACR White Paper considers resection when it is not a lipid-rich adenoma or another characteristic benign lesion.
- A lesion stable for at least 1 year does not require further imaging. Hormonal evaluation should be considered in most incidentalomas.
Source
Mayo-Smith WW et al. Management of Incidental Adrenal Masses: A White Paper of the ACR Incidental Findings Committee. JACR 2017;14(8):1038-1044. DOI 10.1016/j.jacr.2017.05.001
The same logic runs in the public tool of RadCommons, the Laudos.AI classification corpus.
Questions and answers
How is absolute adrenal washout calculated?
Absolute washout = 100 × (portal venous phase attenuation − delayed phase attenuation) ÷ (portal venous phase attenuation − unenhanced attenuation), with the three attenuation values in HU and the delayed phase at 15 minutes.
What washout value is consistent with adenoma?
By the 2017 ACR White Paper, absolute washout of 60% or more, or relative washout of 40% or more. Unenhanced attenuation of up to 10 HU already indicates a lipid-rich adenoma, with no need for washout.
When should relative washout be used?
When the exam has no unenhanced phase. Relative washout uses only the portal venous and delayed phases: 100 × (portal venous − delayed) ÷ portal venous.
Does high washout guarantee that it is an adenoma?
No. Hypervascular metastasis (such as renal cell or hepatocellular carcinoma) and pheochromocytoma can have high washout. The result is interpreted with the clinical picture.
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