Traumatic axonal injury: practical issues for diagnosis in medicolegal cases

In the 25 years or so after the first clinicopathological descriptions of d iffuse axonal injury (DAI), the criterion for diagnosing recent traumatic w hite matter damage was the identification of swollen axons ('bulbs') on rou tine or silver stains, in the appropriate clinical setting. In the last dec ade, however, experimental work has given us greater understanding of the c ellular events initiated by trauma to axons, and this in turn has led to th e adoption of immunocytochemical methods to detect markers of axonal damage in both routine and experimental work. These methods have shown that traum atic axonal injury (TAI) is much more common than previously realized, and that what was originally described as DAI occupies only the most severe end of a spectrum of diffuse trauma-induced brain injury. They have also revea led a whole field of previously unrecognized white matter pathology, in whi ch axons are diffusely damaged by processes other than head injury; this in turn has led to some terminological confusion in the literature. Neuropath ologists are often asked to assess head injuries in a forensic setting: the diagnostic challenge is to sort out whether the axonal damage detected in a brain is indeed traumatic, and if so, to decide what - if anything - can be inferred from it. The lack of correlation between well-documented histor ies and neuropathological findings means that in the interpretation of assa ult cases at least, a diagnosis of 'TAI' or 'DAI' is likely to be of limite d use for medicolegal purposes.