The military medical system is failing to diagnose brain injuries in troops who served in Iraq and Afghanistan, many of whom receive little or no treatment for lingering health problems, an investigation by ProPublica and NPR has found.

So-called mild traumatic brain injury has been called one of the wars’ signature wounds. Shock waves from roadside bombs can ripple through soldiers’ brains, causing damage that sometimes leaves no visible scars but may cause lasting mental and physical harm.

Officially, military figures say about 115,000 troops have suffered mild traumatic brain injuries since the wars began. But top Army officials acknowledged in interviews that those statistics likely understate the true toll. Tens of thousands of troops with such wounds have gone uncounted, according to unpublished military research obtained by ProPublica and NPR.

ProPublica: Brain Injuries Remain Undiagnosed in Thousands of Soldiers

This is a long one. If you want to read a shorter version, here’s NPR’s coverage.