Prognostic Implications of the Periaortic Fat Attenuation Index in Uncomplicated Type B Aortic Dissection

Purpose To evaluate the prognostic value of the periaortic fat attenuation index (FAI), which noninvasively captures vascular inflammation on noncontrast CT images, in managing uncomplicated type B aortic dissection (TBAD). Materials and Methods In this retrospective multicenter study (January 2011-December 2022), an automated machine learning algorithm measured periaortic FAI of the descending thoracic aorta at noncontrast CT. Patients who underwent CT for chest or back pain were included to compare FAI between those with acute aortic dissection, including both type A and B, and those without. Further, prognostic evaluation of patients with uncomplicated TBAD was conducted using multivariable Cox proportional hazards regression. Results A total of 688 patients (median age, 69 years [IQR, 56-79]; 400 male patients), including 380 with acute aortic dissection and 308 without, were analyzed for the diagnostic characteristics of FAI, and 135 patients with uncomplicated TBAD (median age, 70 years [IQR, 59-79]; 90 male patients) were followed up for prognosis. FAI values at initial presentation were higher in patients with acute aortic dissection than in those without (median, -74.5 vs -78.7 HU; <i>P</i> < .001). In patients with uncomplicated TBAD, FAI values peaked on the 6th day after onset. These patients were divided into two groups according to the median peak FAI value of -64 HU. During a median follow up of 529 days, those with higher peak FAI values (≥-64 HU) had higher rates of all-cause death and aortic events (log-rank <i>P</i> < .001). High peak FAI independently predicted these events (adjusted hazard ratio, 4.54 [95% CI: 1.69, 12.21]; <i>P</i> = .003). Conclusion A higher peak FAI value was an independent risk factor for adverse events in patients with uncomplicated TBAD. <b>Keywords:</b> Acute Aortic Dissection, Fat Attenuation Index, Noncontrast CT, Perivascular Adipose Tissue, Prognosis UMIN Clinical Trials Registry (AIDFAI study no. UMIN000053435). <i>Supplemental material is available for this article.</i> © The Author(s) 2025. Published by the Radiological Society of North America under a CC BY 4.0 license.