Adrenal Washout Calculator

Determines absolute and relative washout based on pre and post contrast and 15 minutes delayed CT scans.

Refer to the text below the tool for more information about the formulas employed and their usage.


Both lipid-rich and lipid-poor adenomas rapidly wash out contrast, whereas non-adenomas (e.g. metastases) take longer to washout.

Absolute and relative adrenal washout may be determined via formulas based on three elements, all in Hounsfield units:

  • Pre-contrast CT;
  • A contrast-enhanced (post-contrast) CT with a delay of 60-75 seconds;
  • A 15 minutes delayed phase CT.

  • Absolute Washout = 100 x (Post contrast HU – Delayed phase HU) / (Post contrast HU – Pre contrast HU)
  • Relative Washout = 100 x (Post contrast HU – Delayed phase HU) / Post contrast HU

Interpretation

  • Absolute washout ≥ 60% is strongly suggestive of adrenal adenoma.
  • Relative washout ≥ 40% is strongly suggestive of adrenal adenoma.
  • Regardless of absolute or relative washout, if pre-contrast attenuation is low (<10 HU), then adenoma should be further investigated.

Pre-contrast HU
60-75 second post-contrast HU
15 minutes delayed phase HU
HU = Hounsfield Unit, which is defined as the relative quantitative measurement of radio density used by radiologists in the interpretation of computed tomography images.
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Adrenal Washout Explained

Adrenocortical adenoma is a benign tumor that is either functional (hormonally active) or non-functioning (hormonally inactive) and is usually asymptomatic, found via unrelated CT scan. Non-functioning adenomas have a good prognosis whilst functional adenomas may complicate to Cushing syndrome, virilization, or hyperaldosteronism.

Both lipid-rich and lipid-poor adenomas rapidly wash out contrast, whereas non-adenomas (e.g. metastases) take longer to washout. If during a CT, the unenhanced, pre-contrast CT of les than 10 HU is indicative of lipid-rich adenoma. For values >10HU, if absolute washout is more than 60%, then that is a lipid-poor adenoma.

Absolute and relative adrenal washout may be determined via formulas based on three elements, all in Hounsfield units:

  • Pre-contrast CT;
  • A contrast-enhanced (post-contrast) CT with a delay of 60-75 seconds;
  • A 15 minutes delayed phase CT.

Formulas

  • Absolute Washout = 100 x (Post contrast HU – Delayed phase HU) / (Post contrast HU – Pre contrast HU)
  • Relative Washout = 100 x (Post contrast HU – Delayed phase HU) / Post contrast HU

Interpretation

  • Absolute washout ≥ 60% is strongly suggestive of adrenal adenoma.
  • Relative washout ≥ 40% is strongly suggestive of adrenal adenoma.
  • Regardless of absolute or relative washout, if pre-contrast attenuation is low (<10 HU), then adenoma should be further investigated.

In a study by Caoili et al. of 61 adrenal masses of pre-contrast CT of at least 10 HU, sensitivity and specificity were 86% and 92% for absolute washout and 82% and 92% for relative washout.

Washout measurements may have significantly reduced specificity in the case of renal or hepatocellular carcinoma.

A substantial minority of pheochromocytomas (30-45%) have absolute or relative washout characteristics that overlap with those of lipid-poor adenomas.

Pre-contrast CT attenuation of more than 43 HU in a noncalcified, non-hemorrhagic lesion is suspicious for malignancy, regardless of absolute or relative washout.

Inhomogeneous lesions with large areas of necrosis or hemorrhage cannot be characterized via washout pattern.

 

References

Slattery JM, Blake MA, Kalra MK, et al. Adrenocortical carcinoma: contrast washout characteristics on CT. AJR Am J Roentgenol. 2006; 187(1):W21-W24.

Sahdev A, Willatt J, Francis IR, Reznek RH. The indeterminate adrenal lesion. Cancer Imaging. 2010; 10(1):102-13.

Boland GW, Lee MJ, Gazelle GS, et al. Characterization of adrenal masses using unenhanced CT: an analysis of the CT literature. American Journal of Roentgenology. 1998; 171(1):201–204.

Blake MA, Cronin CG, Boland GW. Adrenal imaging. AJR Am J Roentgenol. 2010; 194 (6): 1450-60.

Patel J, Davenport MS, Cohan RH et-al. Can established CT attenuation and washout criteria for adrenal adenoma accurately exclude pheochromocytoma?. AJR Am J Roentgenol. 2013; 201 (1): 122-7.

Blake MA, Kalra MK, Sweeney AT, et al. Distinguishing benign from malignant adrenal masses: multi-detector row CT protocol with 10-minute delay. Radiology 2005; 238:578-585.

Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology 2002; 222:629-633.


Specialty: Oncology

System: Endocrine

Objective: Diagnosis

Article By: Denise Nedea

Published On: July 13, 2020

Last Checked: July 13, 2020

Next Review: July 13, 2025