Frequency of Diffuse Axonal Injury and Its Outcomes in Severe Traumatic Brain Injury (sTBI): A Systematic Review and Meta-Analysis

While it is established that diffuse axonal injury (DAI) is a leading cause of death or disability among patients with traumatic brain injury (TBI), less is known about the frequency of DAI in patients with severe TBI (sTBI). Additionally, little is known about the mortality rate and proportion of males/females among patients with both sTBI and DAI. We conducted a systematic literature search in the databases EMBASE Ovid, PubMed, Scopus, and Web of Science Advance from inception until April 22, 2024. No filters or language restrictions were applied. Two reviewers (A.S. and P.S.) independently screened the obtained abstracts and full texts. We included full-text studies that reported the frequency of DAI after TBI or any measure of association between DAI and clinical outcome (e.g., death, Glasgow Outcome Scale). Animal studies, reviews, and non-original research articles were excluded. We qualitatively described the results of the included studies. Thirty-seven studies met our inclusion criteria: 18 retrospective, 18 prospective, and 1 was both retrospective and prospective, representing studies from 14 countries. Thirty-three were single-center studies, and four were multicenter. Five studies were exclusively conducted among pediatric patients, while the remaining 32 included adults. The pooled proportion of DAI among sTBI patients was 0.60 (95% confidence interval [CI]: 0.39, 0.78]), I 2 = 98%. The pooled mortality among patients with both sTBI and DAI is 0.16 [95% CI: 0.07, 0.30], I 2 = 12%. The pooled proportion of males among individuals with both sTBI and DAI was 0.81 [95% CI: 0.76, 0.85], I 2 = 46%. DAI is common in patients with sTBI. The comorbid state of having both sTBI and DAI can be life-threatening and is more often seen in males than females, possibly due to the increased tendency of males to partake in risky behaviors that increase the likelihood of head trauma. There might be a difference in outcome after DAI between the pediatric and adult patient populations, possibly due to increased plasticity of brain tissue in younger patients.