How can the diagnosis of adrenal adenoma be confirmed on enhanced CT?

If a lesion is found on contrast-enhanced CT scan, a 15 minute delayed scan can confirm that it is a benign lesion if it measures less than 30 HU on delayed CT after contrast. Washout calculations:
E Enhanced
D 15 minute delayed
U Unenhanced
Percentage of enhancement washout = [(E - D) / (E - U)] x 100. Using threshold of 60%, 88% sensitive, 96% specific.
Percentage of relative enhancement washout = [(E - D) / E x 100. Using threshold of 40%, 96% sensitive, 100% specific.