CT rapid contrast bleaching distinguishes adrenal adenomas from non-adenomas [Classics Series]

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of Historical Trials

1. The average percentage of contrast bleaching on computed tomography (CT) was significantly greater for adenomas than for non-adenomas in all late scans.

2. Delayed computed tomography distinguished adenomas from non-adenomas with high sensitivity and specificity at different time points, as early as 5 to 15 min after improvement.

Originally Posted: March 1998

Study rundown: Adrenal mass lesions were detected incidentally in up to 5% of patients exposed to CT for indications unrelated to adrenal disease. In patients with no known history of cancer, most of these lesions are benign. For patients diagnosed with a malignant tumor outside the adrenal gland, the probability that an incidentally discovered adrenal lesion is malignant is greatly increased. On unenhanced CT, benign adrenal adenomas are characterized by low attenuation. However, on contrast-enhanced tomography, attenuation values ​​cannot differentiate between benign and malignant lesions. As such, other imaging modalities or frequent imaging have historically been used to distinguish between benign and malignant adrenal masses. This was until several studies noted that intravenous (IV) contrast medium tends to “wash out” faster from glandular lesions than from non-neoplastic lesions, and thus, CT attenuation measurements after a variable delay can be used to characterize adrenal lesions. Given that measurements of late CT attenuation are dependent on type, total dose, and rate of intravenous contrast injection, however, measures of absolute attenuation in late scans were found to be unhelpful. In response, the use of enhanced bleaching curves has been proposed to distinguish adrenal adenomas from non-adenomas. In this study by Korobkin and colleagues, contrast-enhanced bleaching curves were generated after delayed computed tomography for adrenal adenomas and non-adenomas. The results of this study showed that the average percentage of enhancement exacerbations for adrenal adenomas far exceeded that observed in non-adenomas. The authors also showed that delayed CT scans can distinguish adenomas from non-adenomas with high sensitivity and specificity at different time points, as early as 5–15 min after improvement. Pina and colleagues later confirmed in their study that the relative percentage of deviation in dynamic and delayed CT scans can be used to characterize adrenal masses.

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in depth [prospective cohort]: Patients with adrenal masses identified by computed tomography of the abdomen or chest respectively were enrolled in this study. The diagnosis of adrenal adenoma was confirmed by various means, including percutaneous biopsy, stable appearance on follow-up CT scans and an attenuation value <10 Hounsfield units (HU) on unenhanced CT. The diagnosis of non-adenoma was confirmed by surgery, percutaneous biopsy, significant growth or contraction at short-term follow-up, and computed tomography of one case of medullary lipoma. Enhanced and non-enhanced scans were obtained for all adrenal masses, and delayed CT values ​​were studied in two groups of patients. In the first group, delayed scans were acquired at 15, 30 and 45 min after the initial enhanced CT scan. In the placebo group, delayed scans were acquired at 5, 10, and 15 min after the initial enhanced CT scan. From these scans, the percentages of primary enhancement at these time points were calculated and used to generate bleaching curves for adrenal adenomas and non-adrenal adenomas. Sensitivity and specificity calculations for diagnosing adenoma were performed using delayed CT scans after selecting the optimal threshold value. A total of 66 patients with 76 adrenal masses were evaluated. The masses consisted of 52 adenomas (n = 45; median age 64 years, range 43-80 years; 53% men) and 24 non-adenomas (n = 21; median age 60 years, range 31-76 years). ; 71% men). Consistent with previous studies, there was no significant difference in mean CT attenuation at initial enhancement of glandular versus non-adipose masses. However, a statistically significant difference in mean CT attenuation was observed between adenomas and unenhanced non-adenomas (P < 0.001) and all late enhanced scans (P < 0.001). For unboosted scans, an optimal threshold of 10 HU corresponds to a sensitivity of 87% and a specificity of 100%. For the 15-min delayed enhanced scan, both sensitivity and specificity were 96% at a threshold of 37 HU. Differences in the mean percentages of initial enhancement were also found to be statistically significant between the adenoma and non-adenoma groups at all late times (p < 0.001). The mean percentage of bleach-enhancing adrenal gland tumors was 51% at 5 minutes and 70% at 15 minutes, compared to 8% and 20% for non-adrenal adenomas, respectively. In the 15-min delayed enhanced scans, the optimal threshold for diagnosing adenoma was set at 60% of the enhanced variance, associated with a sensitivity of 88% and a specificity of 96%.

Kurupkin M, Broodor FG, Francis IR, Quint Lee, Denek NR, Lundy FCT Temporal attenuation attenuation curves for adrenal adenomas and non-adenomatous tumors. American Journal of Oncology. 1998 Mar; 170 (3): 747-52.

Additional review:

Blake MA, Cronin CG, Poland GW. Adrenal gland imaging. American Journal of Oncology. 2010; 194 (6): 1450.

Poland JWL, Blake MA, Han BF, May Smith WW. Symptomatic adrenal lesions: principles, techniques, and algorithms for imaging characterization. X-rays. 2008 Dec; 249 (3): 756–75.

Peña CS, Boland JWL, Hahn BF, LiMG, Muller BR. Characterization of indeterminate (lipid-poor) adrenal masses: use of bleaching properties when contrast-CT . enhancement. X-rays. 2000 Dec; 217 (3): 798–802.

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