A 55-year-old woman with history of hypertension, melanoma, and urolithiasis is found to have a left adrenal mass on a non-contrast computed tomography (CT) scan evaluation obtained to assess renal colic.
The mass measures 2.5 cm in diameter and demonstrates an attenuation of 30 Hounsfield units (HU). A metabolic work-up rules out hypercortisolemia and hyperaldosteronemia. Plasma free metanephrines are within normal limits, excluding the possibility of pheochromocytoma.
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C: The goal of adrenal imaging is to differentiate benign adrenal adenomas from other adrenal lesions. Some 70% of adenomas are lipid-rich and exhibit low-density attenuation on non-contrast CT. In fact, an adrenal lesion that is less than 10 HU in density on non-contrast CT can be deemed an adenoma with an extremely high degree of certainty.1 Approximately 30% of adenomas, as in the above example, are lipid-poor and exhibit an attenuation of greater than 10 HU on non-contrast CT.2-4 For these lipid-poor adrenal lesions, there is a temptation to obtain an MR study for better characterization; however, adrenal protocol MR—which harnesses opposed phase chemical-shift strategies to quantify intracellular lipid within adrenal lesions—is only marginally superior to non-contrast CT in identifying adenomas.5, 6 As such, the go-to study for a lipid-poor adrenal lesion is a 15-minute CT washout study. Adrenal masses that “washout,” or lose more than 40%-60% of contrast enhancement 15 minutes after the contrast bolus, are managed as adenomas, since the specificity of an adrenal washout study is extremely high.2-4, 7 An adrenal washout calculator can be found at www.cancernomograms.com. Gadolinium contrast agents do not exhibit the same washout properties as does iodinated contrast. Thus, CT washout is a far superior study for characterizing adrenal lesions than MR imaging.8 Regardless of radiographic characteristics, every adrenal lesion requires an appropriate metablic work-up.9
1. Grumbach, MM, Biller BMK, Braunstein GD, et al. Management of the clinically inapparent adrenal mass (“Incidentaloma”). Ann Intern Med. 2003;138:424-429.
2. Szolar, DH, Korobkin M, Reittner P, et al. Adrenocortical carcinomas and adrenal pheochromocytomas: Mass and enhancement loss evaluation at delayed contrast-enhanced CT. Radiology. 2005;234:479-485.
3. Korobkin M, Brodeur FJ, Francis IR, et al. CT time-attenuation washout curves of adrenal adenomas and nonadenomas. Am J Roentgenol. 1998;170:747-752.
4. Pena CS, Boland GWL, Hahn PF, et al. Characterization of indeterminate (lipid-poor) adrenal masses: Use of washout characteristics at contrast-enhanced CT. Radiology. 2000;217:798-802.
5. Israel GM, Korobkin M, Wang C, et al. Comparison of unenhanced CT and chemical shift MRI in evaluating lipid-rich adrenal adenomas. Am J Roentgenol. 2004;183:215-219.
6. Haider MA, Ghai S, Jhaveri K, et al. Chemical shift MR imaging of hyperattenuating (>10 HU) adrenal masses: Does it still have a role? Radiology. 2004;231:711-716.
7. Boland GW, Blake MA, Hahn PF, et al. Incidental adrenal lesions: principles, techniques, and algorithms for imaging characterization. Radiology. 2008;249:756-775.
8. Hussain HK, Korobkin M. MR imaging of the adrenal glands. Magn Reson Imaging Clin N Am. 2004;12:515-544.
9. Kutikov A, Crispen PL, Uzzo RG. Pathophysiology, evaluation, and medical management of adrenal disorders. In: Campbell-Walsh Urology, 10th ed. Edited by A. J. Wein, L. R. Kavoussi, A. W. Partin et al. Philadelphia: Elsevier, p. in press, 2011