Diagnostic Agreement and Prognostic Value of Clinically Interpreted CT Vs MRI for Incidentally Discovered Covert Cerebrovascular Disease.

BACKGROUND AND OBJECTIVES:Studies of covert cerebrovascular disease (CCD) typically rely on MRI screening, whereas CT is the predominant imaging modality in routine care. We aimed to determine the diagnostic agreement of clinically interpreted CT and MRI for incidentally discovered CCD and to compare the modality-specific prognostic implications of these findings. METHODS:We conducted a retrospective cohort study within Kaiser Permanente Southern California. Adults aged ≥50 years without previous stroke or dementia who underwent both head CT and brain MRI within 30 days (2009-2022) were included. Natural language processing was used to identify covert brain infarction (CBI) and white matter disease (WMD) and to grade WMD severity from reports. The primary outcome was incident ischemic stroke or dementia. Associations between modality-specific CCD findings and outcomes were estimated using Cox proportional hazards models adjusted for age, sex, race/ethnicity, vascular risk factors, and dementia risk factors. RESULTS:Among 18,628 participants (mean age 64.9 years; 59.1% female), CBI prevalence was similar on CT (6.3%) and MRI (6.1%), with modest agreement (κ = 0.27). WMD was more frequently reported on MRI (60.5%) than CT (24.4%), with modest agreement (κ = 0.23). Nearly half of the patients with graded WMD showed discordant severity across modalities, most often (92%) with higher severity on MRI. Over a mean 4.4-year follow-up, incidence rates of stroke or dementia per 1,000 person-years were 12.7 (95% CI 11.5-14.0) for patients negative on both modalities, 22.6 (21.0-24.2) for WMD reported on MRI only, 37.0 (29.8-45.6) for WMD reported on CT only, and 52.2 (48.7-56.0) for WMD reported on both modalities. Compared with patients negative on both modalities, adjusted hazard ratios were 1.23 (95% CI 1.07-1.41) for MRI-only WMD and 1.82 (1.58-2.11) for WMD reported on both modalities. DISCUSSION:MRI detects WMD more frequently and assigns higher severity than CT; however, WMD detected on CT identifies a subgroup at substantially higher risk than those with MRI-only findings. These findings highlight the importance of modality-specific interpretation of CCD in clinical practice and research. Limitations include reliance on radiology reports rather than direct image review and the selected population undergoing both imaging modalities.