Traumatic Microhemorrhages Are Not Synonymous With Axonal Injury

Diffuse axonal injury (DAI) is caused by acceleration-deceleration forces during trauma that shear white matter tracts. Susceptibility-weighted MRI (SWI) identifies microbleeds that are considered the radiologic hallmark of DAI and are used in clinical prognostication. However, this assumption is limited by a lack of systematic radiologic-pathologic correlation studies. Here, we performed ex vivo SWI on three brains from patients who died after severe TBI and assessed axonal injury around SWI microbleeds using immunohistochemistry to the amyloid-beta precursor protein. Axonal injury was present in 64% of microbleeds, indicating a heterogeneous injury response in the white matter.