Adrenal washout

Dr Henry Knipe ◉ ◈ and Dr Maxime St-Amant ◉ et al.

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

Pheochromocytomas may also wash out, 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.

Lesions that are inhomogeneous or with large areas of necrosis or hemorrhage cannot be characterized by their washout pattern ⁶.