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Adrenal CT Washout Calculator

Calculate Absolute and Relative Washout to characterize adrenal masses.

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Inputs

HU
HU
HU

Your values stay on this device.

Results

Absolute Washout
Relative Washout62.50%
InterpretationLikely Adenoma (Absolute > 60%)

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Assumptions

  • The formula assumes attenuation values come from a comparable ROI placement across phases.
  • The output is a characterization aid and does not replace the full imaging appearance, growth history, or endocrine workup.
  • Thresholds vary by protocol timing and institutional practice, so this tool should not be treated as a stand-alone diagnosis.

Sensitivity preview

Pre-Contrast (Unenhanced) -10%: Absolute Washout 76.90%

Pre-Contrast (Unenhanced) Current: Absolute Washout 78.90%

Pre-Contrast (Unenhanced) +10%: Absolute Washout 81.10%

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About this Adrenal Washout

Adrenal incidentalomas are common findings on CT scans. Washout calculations help radiologists differentiate lipid-poor adenomas (benign) from malignant lesions (metastases) based on how quickly the contrast medium washes out of the tissue.

Who this calculator is for

  • Radiologists, trainees, and imaging staff reviewing adrenal protocol CT measurements.
  • Clinicians who already have attenuation values from unenhanced, enhanced, and delayed phases.
  • Learners studying how absolute and relative washout are used in adrenal lesion workups.

When to use it

  • Use this calculator after ROI measurements have already been collected from the adrenal lesion on the relevant phases.
  • Use it to compare absolute and relative washout when a complete adrenal protocol CT is available.
  • Use it as an educational check when documenting why a lesion remains indeterminate versus adenoma-favoring.

How to use this calculator

  1. Enter Pre-Contrast HU (Unenhanced). Leave blank or 0 if unavailable.
  2. Enter Portal Venous HU (Enhanced, typically 60-70 sec delay).
  3. Enter Delayed HU (Typically 15-minute delay).
  4. Check the Diagnosis below.

Key assumptions

  • The formula assumes attenuation values come from a comparable ROI placement across phases.
  • The output is a characterization aid and does not replace the full imaging appearance, growth history, or endocrine workup.
  • Thresholds vary by protocol timing and institutional practice, so this tool should not be treated as a stand-alone diagnosis.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

* Relative Washout: (Enhanced - Delayed) / Enhanced * Absolute Washout: (Enhanced - Delayed) / (Enhanced - Pre-Contrast) Adenomas wash out contrast faster than metastases or pheochromocytomas.

Inputs explained

Pre-Contrast

Density of the lesion before contrast injection. If < 10 HU, it is likely a lipid-rich adenoma.

Enhanced (Venous)

Density during the portal venous phase.

Delayed

Density after a 15-minute delay.

Understanding your results

Absolute Washout ≥ 60% or Relative Washout ≥ 40% strongly suggests a benign Adenoma. Values below these thresholds are indeterminate/suspicious.

Key Features

  • Calculates Absolute & Relative Washout
  • Automatic Diagnostic Interpretation
  • Handles missing pre-contrast values

Frequently Asked Questions

What indicates an Adenoma?
An Absolute Washout > 60% or a Relative Washout > 40% is highly specific for a benign adrenal adenoma.
When can I use Relative Washout?
Relative washout is used when a pre-contrast scan was not performed. It compares the venous phase directly to the delayed phase. It is slightly less specific than absolute washout.
What if the Pre-contrast HU is < 10?
If the unenhanced density is < 10 HU, the lesion is likely a lipid-rich adenoma, and washout calculations are generally unnecessary.