This study summary is an excerpt from 2 Minute Medicine’s book The Classics in Medicine: Summaries of the Landmark Trials
1. The mean percent computed tomography (CT) contrast washout was significantly greater for adenomas compared to non-adenomas in all delayed scans.
2. Delayed enhanced CT scans distinguished adenomas from non-adenomas with high sensitivity and specificity at different time points, as early as 5 to 15 minutes after improvement.
Original Publication Date: March 1998
Study overview: Adrenal mass lesions are incidentally detected in up to 5% of patients undergoing CT for indications unrelated to adrenal disease. In patients with no known cancer history, most of these lesions are benign. In patients with a diagnosed extraadrenal malignancy, the chance that an incidentally discovered adrenal lesion is malignant increases significantly. On unenhanced CT scans, benign adrenal adenomas are characterized by low attenuation. However, on contrast-enhanced CT, attenuation values cannot distinguish between benign and malignant lesions. As such, other imaging modalities or repeated imaging have been used in the past to distinguish between benign and malignant adrenal masses. This was until several studies noted that intravenous (IV) contrast agent tended to “wash” out of adenomatous lesions more quickly than non-adenomatous lesions, and therefore CT attenuation measurements could be used after a variable lag period to characterize adrenal lesions. However, since delayed CT attenuation measurements depend on the type, total dose, and injection rate of IV contrast material, measurements of absolute attenuation on delayed scans have not been shown to be useful. In response, the use of washout curves has been proposed to distinguish adrenal adenomas from non-adenomas. In this study, conducted by Korobkin and colleagues, contrast enhancement washout curves were generated after delayed contrast-enhanced CT scans of adrenal adenomas and non-adenomas. The results of this study showed that the mean rate of improvement washout for adrenal adenomas was much higher than that observed in non-adenomas. The authors also showed that delayed enhanced CT scans could distinguish adenomas from non-adenomas with high sensitivity and specificity at different time points, as early as 5 to 15 minutes after improvement. Pena and colleagues later confirmed in their study that the relative percentage washout on dynamic and delayed-enhanced CT scans could be used to characterize adrenal masses.
Click to read the study in ARRS
in-depth [prospective cohort]: Patients with adrenal masses identified by abdominal or chest CT were sequentially included in this study. Diagnosis of adrenal adenoma was confirmed by several means, including percutaneous biopsy, stable appearance on follow-up CT examinations, and an attenuation value of <10 Hounsfield Units (HU) on unenhanced CT. The diagnosis of nonadenoma was confirmed by surgery, percutaneous biopsy, substantial growth or shrinkage at short follow-up and stable CT for 1 case of myelolipoma. Unenhanced and standard enhanced scans were obtained for all adrenal masses and delayed enhanced CT values were studied in 2 groups of patients. In the first group, delayed scans were obtained 15, 30 and 45 minutes after the initial enhanced CT. In the second group, delayed scans were obtained at 5, 10 and 15 minutes after the initial enhanced CT. From these scans, percentages of initial improvement at these time points were calculated and used to generate washout curves for adrenal adenomas and non-adenomas. Calculations of sensitivity and specificity for the diagnosis of adenoma using delayed enhanced CT were made after selecting an optimal threshold value. A total of 66 patients with 76 adrenal masses were evaluated. The masses consisted of 52 adenomas (n=45; mean age 64 years, range 43-80 years; 53% males) and 24 non-adenomas (n=21; mean age 60 years, range 31-76 years; 71% males ). Consistent with previous studies, there was no significant difference in mean CT attenuation at initial gain for adenomatous versus non-adenomatous masses. However, a statistically significant difference in mean CT attenuation between adenomas and non-adenomas was observed for unenhanced (p < 0.001) and all delayed enhanced (p < 0.001) scans. For unenhanced scans, an optimal threshold of 10 HU corresponded to a sensitivity of 87% and a specificity of 100%. For the 15 min delayed enhanced scan, the sensitivity and specificity were both 96% at a threshold of 37 HU. Differences in mean percentages of initial improvement were also found to be statistically significant between the adenoma and non-adenoma groups at all delayed time points (p < 0.001). The mean percent improvement washout for adrenal adenomas was 51% at 5 minutes and 70% at 15 minutes, compared to 8% and 20% for non-adenomas, respectively. On the 15 minute delayed enhanced scans, an optimal threshold for adenoma diagnosis was established at 60% contrast enhancement washout, associated with a sensitivity of 88% and specificity of 96%.
Korobkin M, Brodeur FJ, Francis IR, Quint LE, Dunnick NR, Londy F. CT time-attenuation washout curves of adrenal adenomas and nonadenomas. American Journal of X-rays. 1998 Mar;170(3):747-52.
Additional review:
Blake MA, Cronin CG, Boland GW. Adrenal imaging. American Journal of X-rays. 2010;194(6):1450.
Boland GWL, Blake MA, Hahn PF, Mayo-Smith WW. Occasional Adrenal Lesions: Imaging Principles, Techniques and Algorithms. Radiology. 2008 Dec;249(3):756-75.
Peña CS, Boland GWL, Hahn PF, Lee MJ, Mueller PR. Characterization of indeterminate (lipid-poor) adrenal masses: using washout features in contrast-enhanced CT. Radiology. 2000 Dec;217(3):798-802.
©2022 2 Minute Medicine, Inc. All rights reserved. No work may be reproduced without the express written permission of 2 Minute Medicine, Inc. Ask about licenses here. No article should be construed as medical advice and is not intended as such by the authors or by 2 Minute Medicine, Inc.
.