CT Adrenal Washout
Enter Hounsfield unit measurements from unenhanced, portal venous (60–90 seconds), and delayed (10–15 minutes) phases to differentiate benign adenomas from suspicious lesions.
Pre-contrast attenuation value
60–90 seconds post contrast
10–15 minutes post contrast
Absolute washout
67.1%
Relative washout
61.1%
Interpretation
Consistent with lipid-poor adenoma
How to Use This Calculator
Measure attenuation values
Use consistent region-of-interest placement across phases and avoid necrotic or calcified areas to reduce measurement error.
Enter HU values
Ensure the portal venous phase represents peak enhancement, typically 60–90 seconds after contrast administration.
Combine with clinical context
Review lesion size, growth, hormonal findings, MRI chemical shift imaging, and patient history to finalise management.
Formula
Absolute washout (%) = ((Portal − Delayed) ÷ (Portal − Unenhanced)) × 100
Relative washout (%) = ((Portal − Delayed) ÷ Portal) × 100
Absolute washout ≥60% or relative washout ≥40% indicates benign adenoma.
Full Description
Adrenal washout analysis leverages the rapid contrast clearance of adenomas compared with metastases or pheochromocytomas. Values are most reliable when delayed imaging occurs 10–15 minutes after contrast and the lesion is homogeneous. Always integrate imaging findings with endocrine evaluation and patient history (malignancy, growth trends) to guide management.
Frequently Asked Questions
Do I need washout if unenhanced HU is below 10?
Lesions with HU <10 are typically lipid-rich adenomas. Washout calculations can confirm benignity but are often unnecessary.
What if phase timing is incorrect?
Repeat CT with standard timing or obtain MRI chemical shift imaging. Accurate timing is crucial for washout accuracy.
How do haemorrhagic lesions affect washout?
Heterogeneous lesions may yield unreliable washout metrics. Consider alternative imaging (MRI, PET) if haemorrhage or necrosis is present.
When should biopsy or surgery be considered?
Suspicious washout patterns, increasing size, or hormonal hypersecretion warrant multidisciplinary evaluation, including possible biopsy or adrenalectomy.