Adrenal Washout Calculator: Adenoma vs Non-Adenoma CT

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Unenhanced CT attenuation of the adrenal nodule in Hounsfield Units. Leave out if no pre-contrast phase was acquired (relative washout will still be calculated).
HU
60-75 second post-contrast attenuation of the nodule in Hounsfield Units.
HU
15-minute delayed post-contrast attenuation of the nodule in Hounsfield Units.
HU
Absolute Washout PercentageLikely Adenoma
64.3%

Requires pre-contrast, portal venous, and delayed phases

Relative Washout Percentage45%
Pre-contrast findingLipid-poor (10-43 HU): washout criteria apply for adenoma characterization.
AWP interpretationAWP >= 60%: strongly suggestive of adrenal adenoma (86% sensitivity, 92% specificity).
RWP interpretationRWP >= 40%: strongly suggestive of adrenal adenoma (82% sensitivity, 92% specificity).
64.3 %
Non-adenoma pattern<40Indeterminate40-60Adenoma pattern60+
45 %
Non-adenoma pattern<30Indeterminate30-40Adenoma pattern40+

Washout pattern is consistent with a benign adrenal adenoma.

  • Absolute washout of 64.3% meets the adenoma threshold (>= 60%). Sensitivity 86%, specificity 92% from the Caoili et al. validation study.
  • Relative washout of 45.0% meets the adenoma threshold (>= 40%). Useful when a pre-contrast phase was not acquired.
  • Washout criteria should not be applied to heterogeneous lesions with internal necrosis or hemorrhage, or to known hypervascular primary tumors (renal cell carcinoma, hepatocellular carcinoma).

Next stepThese results are educational. A radiologist should integrate washout values with nodule size, morphology, clinical history, and hormonal workup before any management decision.

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