Silent Stroke in Adult Cardiac Surgery: Mechanisms, Clinical Impact, and Preventive Strategies

Background and Objectives: Overt perioperative stroke remains a feared complication of adult cardiac surgery. Diffusion-weighted magnetic resonance imaging (DWI-MRI) has revealed a more prevalent form of cerebral injury, termed silent stroke or silent brain injury (SBI). Covert ischemic lesions occur without focal neurological deficits but are increasingly associated with postoperative delirium, cognitive decline, and elevated long-term cerebrovascular risk. Despite growing recognition, the true burden, mechanisms, and clinical relevance of SBI remain incompletely integrated into perioperative practice. Materials and Methods: We performed a narrative review of the literature published between January 2000 and December 2025, identified through PubMed/MEDLINE and Scopus. Eligible studies included prospective and retrospective cohorts, randomized trials, systematic reviews, and meta-analyses involving adult patients undergoing coronary artery bypass grafting, valve surgery, or minimally invasive cardiac procedures, with or without cardiopulmonary bypass, and reporting MRI-detected ischemic lesions or validated surrogate markers of cerebral injury. Pediatric studies, transcatheter interventions, case reports, and non-English publications were excluded. Sixty studies met the inclusion criteria. Results: Silent stroke occurred more frequently than clinically apparent stroke, with new DWI-MRI lesions detected in approximately 20-60% of patients following cardiac surgery. Lesions were typically small, multifocal, and embolic in distribution, predominantly affecting cortical and watershed regions. Cardiopulmonary bypass-related factors, including aortic manipulation, cerebral microembolization, hemodilution, hypoperfusion, and impaired oxygen delivery, emerged as key contributors. Several studies demonstrated associations between SBI burden and postoperative delirium, early cognitive dysfunction, and functional decline. Perfusion-based neuroprotective strategies showed mechanistic benefit, although no single intervention conclusively prevented SBI. Conclusions: Silent stroke represents the most frequent form of neurological injury in adult cardiac surgery. Evidence suggests that these covert lesions reflect clinically meaningful cerebral injury, with potential short- and long-term consequences. Recognition of silent stroke as a relevant neurological endpoint supports a shift toward multimodal, perfusion-driven neuroprotective strategies and the routine incorporation of MRI-based outcomes in future cardiac surgical research.