1. What is Adrenal Relative Washout?

Adrenal relative washout is a calculated percentage used in CT imaging to differentiate benign adrenal adenomas from malignant adrenal masses. It measures the rate of contrast material washout from adrenal lesions.

2. How Does the Calculator Work?

The calculator uses the relative washout formula:

Where:

• \( Pre \) — Hounsfield Units pre-contrast
• \( 15min \) — Hounsfield Units at 15 minutes post-contrast
• \( Baseline \) — Hounsfield Units at baseline (delayed phase)

Interpretation: A relative washout >40% is highly suggestive of benign adrenal adenoma, while ≤40% suggests possible malignancy.

3. Importance of Relative Washout Calculation

Details: This calculation is crucial for characterizing incidental adrenal masses found on CT scans, helping to avoid unnecessary biopsies or surgeries for benign lesions.

4. Using the Calculator

Tips: Enter Hounsfield Unit measurements from unenhanced, 15-minute post-contrast, and delayed phase CT scans. All values must be valid numerical measurements.

5. Frequently Asked Questions (FAQ)

Q1: What is the clinical significance of >40% washout?
A: A relative washout >40% has high specificity (approximately 98%) for diagnosing benign adrenal adenomas.

Q2: How does relative washout differ from absolute washout?
A: Relative washout uses pre-contrast values in the denominator, while absolute washout uses 15-minute post-contrast values. Relative washout is generally preferred.

Q3: What are typical HU values for adrenal masses?
A: Benign adenomas typically have pre-contrast HU <10, while malignant lesions often have higher attenuation values.

Q4: Are there limitations to this calculation?
A: The calculation may be less reliable for very small lesions, hemorrhagic masses, or in patients with adrenal cortical carcinoma.

Q5: When is adrenal biopsy indicated?
A: Biopsy is considered when washout calculations are indeterminate or when clinical suspicion for malignancy remains high despite imaging findings.