EAT Thickness and BAT-Related Thermogenesis: Dual Imaging Phenotypes Associated with Hepatic Steatosis Severity in MASLD.

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) is associated with ectopic fat accumulation and alterations in adipose tissue function. However, the relationships of structural and thermogenic adipose imaging markers with hepatic steatosis remain incompletely understood. This study aimed to jointly evaluate the cross-sectional associations of epicardial adipose tissue (EAT) thickness and infrared thermography (IRT)-derived brown adipose tissue (BAT)-related thermogenic activity with controlled attenuation parameter (CAP)-defined hepatic steatosis severity in adults with suspected MASLD. Methods: In this cross-sectional study, 207 adults undergoing clinical evaluation for suspected MASLD underwent transient elastography to obtain the controlled attenuation parameter (CAP) for hepatic steatosis assessment. EAT thickness was measured by transthoracic echocardiography, and BAT-related thermogenic activity was assessed by infrared thermography using the supraclavicular-to-chest temperature difference (ΔTemp). Associations of these adipose imaging phenotypes with CAP were evaluated using correlation analyses, sequential multivariable linear regression models, and BAT-stratified analyses. Results: EAT thickness increased progressively across CAP-defined steatosis grades (p < 0.001) and was positively correlated with CAP (r = 0.637, p < 0.001), whereas ΔTemp decreased with increasing steatosis severity and was inversely correlated with CAP (ρ = -0.277, p < 0.001). In sequential multivariable regression models, EAT thickness remained independently associated with CAP across adjustments for age, sex, body mass index, metabolic variables, and ΔTemp (standardized β = 0.559-0.623; all p < 0.001). Both EAT thickness and ΔTemp were independently associated with CAP in the fully adjusted model, with a stronger association for EAT thickness (standardized β = 0.559 vs. -0.167; p < 0.001 and p = 0.004, respectively). Stratified analyses demonstrated consistent associations between EAT thickness and CAP across both BAT-low and BAT-high activity groups. Conclusions: Greater EAT thickness and lower IRT-derived ΔTemp were independently associated with greater CAP-defined hepatic steatosis severity, with EAT thickness showing the stronger standardized association. These complementary structural and thermogenic imaging correlates warrant prospective evaluation to clarify their directionality and clinical relevance.