EP33 - ECE_2563 - Revisiting the 10-HU threshold: unenhanced CT attenuation in functional adrenal adenomas

Abstract

Although adrenocortical adenomas typically show low unenhanced attenuation (≤10 HU) on CT, this benignity criterion has limited sensitivity, particularly in lipid-poor and hormonally active tumors. We aimed to evaluate unenhanced CT attenuation across different functional and non-functioning adrenal adenoma subtypes. In this retrospective study, 167 surgically proven patients with non-enhanced CT of the adrenals as well as complete clinical and biochemical records were included: unilateral primary aldosteronism (PA) defined by complete or partial biochemical success after adrenalectomy (n = 64), mild autonomous cortisol secretion (MACS) (n = 48), Cushing's syndrome (CS) (n = 31), and compared to non-functioning adrenal adenomas (NFA) (n = 24, no surgical proof). After testing for normality, attenuation values were compared using the Kruskal-Wallis test. Frequencies were compared using Fisher's exact test. Adrenal adenomas in CS showed higher attenuation (19.3 ± 14.0 HU) than PA (10.5 ± 12.7 HU), MACS (6.8 ± 16.0 HU), and NFA (5.4 ± 19.9 HU, P = .003). Notably, lesions with >10 HU were common not only in CS (67.7%) but also in PA (48.4%) and MACS (43.7%). Values >20 HU were significantly more common in CS than in the other groups (51.6%, P = .029). In CS, attenuation correlated positively with baseline cortisol (r = 0.508, P = .035), midnight salivary cortisol (r = 0.454, P = .013), and 1 mg DST (r = 0.611, P < .001). In multivariable analysis, cortisol (P = .014) and 1 mg DST (P = .015) independently predicted attenuation (R2 = 26.2%). Unenhanced CT attenuation >10 HU is common in cortisol-producing adenomas, observed in approximately two-thirds of patients, and is also frequently seen in PA and MACS. This finding should be carefully considered in routine clinical decision-making.