# Adrenal washout calculator: absolute and relative

> Calculate the absolute and relative washout of an adrenal nodule on CT and see the interpretation by the ACR 2017 thresholds, with the line ready…

_Category: · Adrenal CT · ACR 2017 · publicado em 2026-11-10_

Canonical URL: https://www.laudos.ai/en/calculadoras/washout-adrenal

## Page summary

- **What this page explains:** Calculate the absolute and relative washout of an adrenal nodule on CT and see the interpretation by the ACR 2017 thresholds, with the line ready…
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## 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](https://doi.org/10.1016/j.jacr.2017.05.001 "Scientific article (DOI)")

The same logic runs in the public tool of [RadCommons](https://radcommons.laudos.ai/systems/acr-incidental-adrenal-2017 "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.

## Continue here

-   [Ellipsoid volume](https://www.laudos.ai/en/calculadoras/volume-elipsoide "Ellipsoid volume")
-   [PSA density](https://www.laudos.ai/en/calculadoras/densidade-de-psa "PSA density")
-   [Volume doubling time](https://www.laudos.ai/en/calculadoras/tempo-de-duplicacao-de-volume "Volume doubling time")
-   [Post-contrast enhancement](https://www.laudos.ai/glossario/realce-pos-contraste "Post-contrast enhancement")
-   [Incidental finding](https://www.laudos.ai/glossario/achado-incidental "Incidental finding")
-   [CT report templates](https://www.laudos.ai/en/templates/tomografia "CT report templates")

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