Adrenal CT Washout

Absolute (APW) and relative (RPW) percentage washout for an indeterminate adrenal nodule.

Attenuation values

Place an ROI over the same portion of the nodule on each phase. Delayed phase is typically at 15 min.

Unenhanced HU (optional — enables APW)

≤ 10 HU on unenhanced CT = lipid-rich adenoma (no washout needed).

Enhanced HU — portal venous (~60–70 s)

Delayed HU — 15 min

Result

Enter enhanced and delayed HU to begin. Add unenhanced HU for absolute washout.

Absolute washout (APW) —%

Relative washout (RPW) —%

Awaiting input…

Report line will appear here.

Interpretation thresholds. Unenhanced ≤ 10 HU → lipid-rich adenoma (benign; washout not required). APW ≥ 60% = adenoma (lipid-poor); APW < 60% = indeterminate. RPW ≥ 40% = adenoma (use when no unenhanced phase); RPW < 40% = indeterminate. APW = (Enhanced − Delayed) ÷ (Enhanced − Unenhanced) × 100. RPW = (Enhanced − Delayed) ÷ Enhanced × 100.
Caveats. Washout is validated for homogeneous nodules; it is unreliable for very large, heterogeneous, haemorrhagic, or necrotic masses, and pheochromocytoma / adrenal carcinoma / metastases can occasionally show adenoma-range washout. Correlate with size, growth, and clinical/biochemical context.
Reference only — not a substitute for clinical judgment. Based on Caoili et al. (Radiology 2002) and ACR adrenal incidentaloma guidance.