There are three pathophysiological aspects to consider with mild traumatic brain injury. The first that occurs is marked accumulation of glutamate, which essentially destroys cells. It burns cells out. It kills cells. But it’s just part of a major metabolic cascade that is unhelpful to the patient after an injury. Secondly, you have diffuse axonal injury, sheer forces, particularly if a patient has a head that is rotated at the time of the injury. You have sort of a balance between the mid brain and the thalamus and all the rest of the brain is torqued around that. To diagnose this, most people look at CT scans, which won’t show it very well at all. The majority do not. MRI T2 weighted will do that. And then probably one of the neatest new tools is tensor diffusion imaging, which is just wonderful.
The third issue is that the blood-brain barrier, which is responsible for keeping things that shouldn’t be in the brain out of the brain, is impacted significantly. There’s two major points here. First you have neurotoxic chemicals coming into the brain because the blood-brain barrier is essentially not working. That state of inappropriate functioning can last for days to a month, so when patients come to see us, and say ‘I had this head injury last week, five days ago…’ even if the problem does not look severe, we can’t give them a final diagnosis. Why? Because if the blood-brain barrier is still dysfunctional, we don’t know. It might take up to a month to really determine what their final injury status would be. So that’s a major impact on dealing with patients.
There are laws in 41 states and the District of Columbia that a child with a sports injury is supposed to be taken out of the game for a minimum of 24 hours. The brain needs to rest. And they can have minor traumatic brain injury from hitting helmet-to-helmet, for instance, without losing consciousness. But really, it takes seven to ten days to fully recover from a significant blow to the head, and during that period of time, prior to recovery, the brain becomes much more vulnerable to a second blow. So, if you have a second blow to the head here because you’re still playing, you’re not resting, that can be turned into a fatal incident. It’s called second impact syndrome. In professional sports, we are more likely to encounter players with chronic traumatic encephalopathy. These are people that for years are hitting head-to-head and routinely will get multiple instances of traumatic brain injury, not just concussion. Over time, it creates significant pathophysiological changes in the brain and so when they retire at the age of 45 or so, there are significant problems with cognition, with memory, with mood, and so on. And this is why chronic traumatic encephalopathy is becoming much more of an issue that we’re trying to deal with.