Adrenal washout

Adrenal washout can be calculated using the density value of an adrenal mass on non-enhanced, portal venous phase and 15 minutes delayed CT scans (density measured in Hounsfield units (HU)). It is primarily used to diagnose adrenal adenoma.

• absolute washout

  • [(HU_{portal venous phase}) - (HU_delayed)] / [(HU_{portal venous phase}) - (HU_non-enhanced)] x 100

  • >60% washout is highly suggestive of adrenal adenoma

• relative washout

  • [(HU_{portal venous phase}) - (HU_delayed)] / (HU_{portal venous phase}) x 100

  • >40% washout is highly suggestive of adrenal adenoma

Practical points

• adrenal washout has limited use when assessing incidental adrenal nodules <4cm in size and <10 HU in patients without known malignancy ⁸

• lesions that are inhomogeneous with large areas of necrosis or hemorrhage cannot be characterized by their washout pattern

• pheochromocytomas and hypervascular metastases (e.g. renal cell carcinoma, hepatocellular carcinoma) may also washout but should have a different clinical presentation; they also may have a higher absolute attenuation on the contrast phase (arterial or portal venous)

• any adrenal lesion >120 HU with washout should not be diagnosed as an adenoma ⁷

See also

Various online calculators are available:

• https://radcalculators.org/adrenal-ct-washout-calculator/

• https://pcheng.org/calc/adrenal_ct.html

• https://www.easycalculation.com/medical/adrenal-washout-calculator.php

• https://radiogyan.com/adrenal-washout-calculator/