Adrenal Washout Calculator

Differentiate lipid-poor adrenal adenoma from non-adenoma using contrast washout on multiphase CT

HU measurements (ROI on adrenal lesion)

Unenhanced (native) HU

Portal-venous / enhanced HU (~60–70 s)

Delayed HU (15 min after contrast)

Tip: native HU ≤ 10 strongly suggests lipid-rich adenoma without need for washout.

Absolute washout (APW)

—

Threshold: APW at least 60 percent suggests adenoma

Relative washout (RPW)

—

Threshold: RPW at least 40 percent suggests adenoma (used when unenhanced HU not available)

Absolute Percentage Washout (APW):

\( \text{APW} = \dfrac{HU_{enh} - HU_{delay}}{HU_{enh} - HU_{native}} \times 100\% \)

Relative Percentage Washout (RPW):

\( \text{RPW} = \dfrac{HU_{enh} - HU_{delay}}{HU_{enh}} \times 100\% \)

Korobkin M et al. Differentiation of adrenal adenomas from nonadenomas using CT attenuation values. AJR 1996;166:531–536. doi:10.2214/ajr.166.3.8623622
Caoili EM et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology 2002;222:629–633. doi:10.1148/radiol.2223010766
ACR Incidental Findings Committee — Adrenal mass white paper (Mayo-Smith 2017).

Washout fails for hypervascular metastases (renal cell, hepatocellular, pheochromocytoma) — interpret in clinical context.