Adrenal Washout Calculator — CT Adenoma vs Non-Adenoma
Enter CT Hounsfield Unit values from the enhanced and delayed phases (and optionally the unenhanced phase) to calculate adrenal washout percentages and determine whether an adrenal incidentaloma favours adenoma.
HU
HU
HU
≥ 40% — likely adrenal adenoma
- 1
Contrast drop (Enhanced − Delayed)
120 − 40 = 80 - 2
Relative washout (RPW)
(80 ÷ 120) × 100 = 66.7RPW ≥ 40% favours adrenal adenoma on CT (Boland et al. 2008).
How does this calculator work?
Adrenal CT washout characterises incidentalomas: APW = (Enhanced − Delayed) / (Enhanced − Unenhanced) × 100 (threshold ≥ 60% for adenoma); RPW = (Enhanced − Delayed) / Enhanced × 100 (threshold ≥ 40%). Use APW when unenhanced HU is available, RPW otherwise. Thresholds are from Boland et al. 2008 and reflect current clinical practice guidelines.
Formula
How this is calculated
Adrenal adenomas are the most common incidental adrenal finding on CT. They characteristically accumulate and then rapidly wash out contrast agent, whereas malignant lesions retain contrast longer. The washout protocol measures CT attenuation (Hounsfield Units, HU) at three time points: before contrast (unenhanced), at the portal venous phase (typically 60 seconds), and at a delayed phase (10–15 minutes).
Absolute percentage washout (APW) uses all three phases: APW = (Enhanced − Delayed) / (Enhanced − Unenhanced) × 100. An APW of 60% or more is highly specific for adenoma. When no unenhanced phase is available, relative percentage washout (RPW) is used instead: RPW = (Enhanced − Delayed) / Enhanced × 100, with a threshold of 40% for adenoma. Both thresholds are based on Boland et al. (2008) and remain widely used clinical criteria.
Thresholds are guidelines, not absolute diagnostic rules. Lipid-poor adenomas may wash out more slowly and fall below the threshold. Phaeochromocytomas can occasionally show high washout values. Any suspicious finding should be evaluated in the full clinical context, and management decisions should not rest on washout alone.
Frequently asked questions
An adrenal incidentaloma is an adrenal mass found unexpectedly on imaging performed for another reason. It is detected in about 4–5% of abdominal CT scans. Most are benign non-functioning adenomas, but the work-up aims to exclude functioning or malignant lesions.
Absolute washout (APW ≥ 60%) is more accurate when an unenhanced phase is available, as it corrects for the baseline attenuation of the mass. Relative washout (RPW ≥ 40%) is used when there is no unenhanced series and is slightly less specific, but still clinically useful.
No. While a high washout strongly favours adenoma, it cannot completely exclude malignancy. Adrenocortical carcinomas and metastases occasionally show higher washout values. Additional features — size, unenhanced attenuation, clinical history, and any growth on follow-up — must all be considered in the overall assessment.
Also known as
TG we-Calculate Editorial Team. (2026). Adrenal Washout Calculator — CT Adenoma vs Non-Adenoma [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/adrenal-washout-calculator
TG we-Calculate Editorial Team. "Adrenal Washout Calculator — CT Adenoma vs Non-Adenoma." TG we-Calculate. 2026. https://we-calculate.com/calculator/adrenal-washout-calculator.
TG we-Calculate Editorial Team, "Adrenal Washout Calculator — CT Adenoma vs Non-Adenoma," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/adrenal-washout-calculator
@misc{wecalculate_adrenal_washout_calculator, title = {Adrenal Washout Calculator — CT Adenoma vs Non-Adenoma}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/adrenal-washout-calculator}}, year = {2026}, note = {TG we-Calculate} }
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