Mild Autonomous Cortisol Secretion Is Associated with Computed Tomography-Derived Hepatic Steatosis in Patients with Adrenal Incidentaloma

Background and Objectives: Mild autonomous cortisol secretion (MACS) has been associated with adverse metabolic outcomes, but its relationship with hepatic steatosis remains incompletely understood. This study aimed to compare computed tomography (CT)-derived hepatic steatosis parameters between patients with MACS and non-functioning adrenal incidentaloma (NFAI) and to evaluate the associations between biochemical markers of cortisol secretion and hepatic attenuation measures. Materials and Methods: This retrospective study comprised 123 patients with adrenal incidentaloma (39 MACS and 84 NFAI) who underwent unenhanced abdominal CT between January 2020 and November 2024. Hepatic steatosis was assessed using mean liver attenuation, liver–spleen attenuation difference, liver-to-spleen attenuation ratio, and conventional CT-defined steatosis thresholds. Non-invasive metabolic indices were also computed. Associations between cortisol secretion parameters and CT-derived hepatic attenuation measures were examined using correlation analysis and multivariable regression. Results: The liver-to-spleen attenuation ratio was lower in the MACS group, although this difference did not reach statistical significance (p = 0.050), and a significantly lower liver–spleen attenuation difference (p = 0.048) was observed compared with the NFAI group, whereas mean liver attenuation (p = 0.167), conventional CT-defined hepatic steatosis, and non-invasive metabolic indices did not differ significantly between groups. Among biochemical markers of cortisol secretion, only 24-h urinary free cortisol showed significant correlations with all CT-derived hepatic attenuation parameters. After adjustment for age, sex, and BMI, urinary free cortisol remained significantly associated with liver–spleen attenuation difference (p = 0.047), whereas its associations with liver attenuation (p = 0.056) and liver-to-spleen attenuation ratio (p = 0.051) did not reach statistical significance. Conclusions: Patients with MACS exhibit subtle CT-derived hepatic fat accumulation despite similar conventional CT-defined steatosis and non-invasive metabolic indices compared with patients with NFAI. Continuous CT-derived attenuation parameters may be more sensitive than conventional CT-defined steatosis thresholds for detecting subtle hepatic fat accumulation associated with mild cortisol excess. The consistent associations observed between 24-h urinary free cortisol and CT-derived hepatic attenuation parameters, including the significant association with liver–spleen attenuation difference after adjustment for age, sex, and BMI, warrant confirmation in larger prospective studies.