Adrenal CT Washout Calculator

Disclaimer: The author makes no claims of the accuracy of the information contained herein; this information is for educational purposes only and is not a substitute for clinical judgment.

 
 
Absolute washout: 100 x Post HU - Delayed HU / Post HU - Pre HU

Relative washout: 100 x Post HU - Delayed HU / Post HU

Adrenal protocol CT has poor performance (57% sensitivity, 84% specificity) for distinguishing adenomas from nonadenomas in heterogeneous nodules (where mixed attenuation occupies >20% of the volume, or there is at least a 30 HU range within a region of interest of at least 0.5 cm2).

Corwin MT, Caoili EM, Elsayes KM, et al. Performance of CT With Adrenal-Washout Protocol in Heterogeneous Adrenal Nodules: A Multiinstitutional Study. AJR Am J Roentgenol 2024; 222(5):e2330769

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%. The non-adenomas included 34 metastases and 2 pheochromocytomas, and the primary malignancy in half of the patients with metastases was lung cancer.

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

A subsequent multicenter study of 336 adrenal nodules at least 1 cm in size in patients without known malignancy (true incidentalomas) showed very limited utility for absolute washout measurements, particularly among nodules <4 cm in diameter. The non-adenomas included 3 metastases, 2 adrenocortical carcinomas, and 9 pheochromocytomas.

Corwin MT, Badawy M, Caoili EM, et al. Incidental Adrenal Nodules in Patients Without Known Malignancy: Prevalence of Malignancy and Utility of Washout CT for Characterization -- A Multi-institutional Study. AJR 2022 Jun 22 [published online]. doi:10.2214/AJR.22.27901