Pathology of blast-related brain injury.

Blasts are responsible for about two-thirds of the combat injuries in Operation Iraqi Freedom and Operation Enduring Freedom, which include at least 1,200 traumatic brain injuries. Blasts inflict damage to the brain directly and by causing injuries to other organs, resulting in air emboli, hypoxia, and shock. Direct injuries to the brain result from rapid shifts in air pressure (primary blast injury), from impacts with munitions fragments and other objects propelled by the explosion (secondary blast injury), and from collisions with objects and rapid acceleration of individuals propelled by the explosion (tertiary blast injury). Tertiary injury can occur from a building or other structure collapsing and from an individual being thrown by the blast wind. The pathological consequences of secondary and tertiary blast injuries are very likely to be similar to those of other types of mechanical trauma seen in civilian life. The damage attributable to the specific effects of a blast, however, has received little study, although it has been assumed to include the focal and diffuse lesions characteristic of closed head injuries. Available clinical studies of blast injuries show focal damage similar to that found in other types of closed head injuries but have not determined whether diffuse axonal injury also occurs. In this article, we will try to reach a better understanding of the specific pathology of blast-related brain injury by reviewing the available experimental studies and the autopsy reports of victims of terrorist attacks and military casualties dating back to World War I.