​

Risk of malignancy is increased for lesions greater than 4 cm in diameter.

Blake MA, Cronin CG, Boland GW. Adrenal imaging. AJR Am J Roentgenol 2010; 194:1450-1460

 

A substantial minority of pheochromocytomas (30-45%) have absolute or relative washout characteristics that overlap with those of lipid-poor adenomas. However, presence of intracytoplasmic lipid in pheochromocytomas (< 10 HU on noncontrast CT) is extremely rare.

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

Schieda N, Siegelman E. Update on CT and MRI of adrenal nodules. AJR Am J Roentgenol 2017; 208:1-12

 

Washout measurements may have significantly reduced specificity in patients with renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or other tumors with hypervascular metastases.

Choi YA, Kim CK, Park BK, et al. Evaluation of adrenal metastases from renal cell carcinoma and hepatocellular carcinoma: use of delayed contrast-enhanced CT. Radiology 2013; 266:514-520

 

Precontrast attenuation of more than 43 HU in a noncalcified, nonhemorrhagic lesion is suspicious for malignancy, regardless of washout characteristics.

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

 

In a study of 61 adrenal masses with noncontrast attenuation at least 10 HU, sensitivity and specificity of absolute washout for adenomas was 86% and 92%, and sensitivity and specificity of relative washout was 82% and 92%.

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