Adrenal Washout Calculator for CT

Calculate the washout of an adrenal nodule based on CT attenuation.

Reference:

Nandra G, Duxbury O, Patel P, Patel JH, Patel N, Vlahos I. Technical and Interpretive Pitfalls in Adrenal Imaging. Radiographics. 2020;40(4):1041-1060. doi:10.1148/rg.2020190080

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More about this calculator:

The Adrenal CT Washout Calculator is a tool used in radiology to assess the likelihood of an adrenal mass being benign or malignant based on its washout characteristics on computed tomography (CT). This assessment helps in the non-invasive differentiation of adrenal adenomas (benign tumors) from malignant lesions such as adrenal carcinomas and metastases.

How It Works

The calculator uses CT imaging data to measure the attenuation (density) of the adrenal lesion at different time points:

Pre-contrast (unenhanced) CT attenuation
Enhanced (contrast) CT attenuation, typically taken 60-70 seconds after contrast administration
Delayed CT attenuation, usually taken 10-15 minutes after contrast administration

The percentage washout is calculated using the following formulas:

Absolute Washout Percentage (AWP):

AWP = ((Enhanced CT Attenuation - Delayed CT Attenuation) / (Enhanced CT Attenuation - Unenhanced CT Attenuation)) * 100
Relative Washout Percentage (RWP):

RWP = ((Enhanced CT Attenuation - Delayed CT Attenuation) / Enhanced CT Attenuation) * 100

Interpretation

Benign Adrenal Adenomas typically show a high washout percentage:
- AWP ≥ 60% or RWP ≥ 40% indicates a high likelihood of a benign adenoma.
Malignant Lesions usually exhibit lower washout percentages, suggesting the need for further investigation or intervention.

Clinical Significance

This method is crucial for avoiding unnecessary surgeries and biopsies by accurately identifying benign adenomas, which can often be managed conservatively. It also aids in the timely identification of potentially malignant lesions that require further diagnostic workup and treatment.

Technical and Interpretive Pitfalls

Variability in Imaging Protocols: Differences in CT scanner calibration, contrast media used, and timing of imaging can affect the accuracy of washout calculations.
Lesion Characteristics: Small lesions or those with necrotic or hemorrhagic components may show atypical washout patterns.
Patient Factors: Variations in patient body habitus and renal function can impact the distribution and clearance of contrast media, influencing washout results.

This tool is invaluable in the non-invasive differentiation of adrenal masses, helping guide clinical management and decision-making.