The Guardian reports that officials fear that up to 20,000 UK soldiers have undiagnosed brain injuries. And the DoD says that up to 20 percent of American soldiers may suffer from "mild traumatic brain injuries." The reason this is such a problem is that soldiers are suffering injuries primarily from blasts, so even if they get checked over, minor bruising and blood clots in the brain may go undetected. This can cause symptoms long associated with post-traumatic stress disorder: anxiety, sleep loss, depression, and violence.
This is an interesting development. I've heard many experts say that often soldiers are unwilling to come forward to getting treated for PTSD because they view it as a weakness. There is still a lingering stigma about needing to visit a therapist, even if it's the result of a terrifying and extended situation such as stationed in a war zone. But now, with new developments in research, veterans may feel better about needing treatment for something that has a physical cause.