What is a traumatic brain injury?

The challenges that need to be overcome to improve outcomes for the many patients who suffer brain injuries were discussed at a recent meeting of the International NeuroTrauma Society here in Cambridge, which is looking to lead the global push for better TBI treatments. We’re going to hear now from Professor of Neurosurgery at the University of Cambridge Peter Hutchinson, who was there, and he gave me an overview of traumatic brain injuries…

Peter - These injuries can be divided into two parts. They can be what we call focal, so that's like a blood clot, which is either between the skull and the membranes or the membranes and the brain, and big blood clots need urgent neurosurgery and an operation to remove them. The second type is what we call diffuse injury, where the brain is swollen and bruised within the confines of the skull. Now if you bruise your knee or your elbow for example, that will swell. It will then go down. The problem when the brain swells is that it's swelling and it's confined by the tight skull. So the consequence of that is the pressure will go up inside the head, and if the pressure goes up, the amount of blood flowing into the brain will reduce delivery of really important nutrients for the brain, like glucose. And the gas, oxygen, that we need to survive on, delivery is reduced. So there is cell death and swelling, which compounds the problem. This vicious cycle of brain swelling in the tight skull, increased pressure, reduction in blood flow, reduction in oxygen, glucose, cell injury, further death and more swelling.

James - And it's a case of the bigger the impact to the head, the worse the injury?

Peter - Diffuse brain injury has a range of severity. The mildest is called mild traumatic brain injury, and the mildest variant of that is called concussion. So that is an injury that can occur with or without loss of consciousness. We don't fully understand what's happening to the brain, but this is usually a transient disturbance of brain function from a number of causes, to more severe diffuse injury through what we call mild/moderate, and the most severe is called diffuse axonal injury in pathological terms. And that's when there is quite severe injury to the structure of the brain, to the nerves and the supporting cells, that is associated with loss of consciousness, which can often be very prolonged and these can be very challenging to treat.

James - It's alarming what you said there about the concussions, on the more mild end of the spectrum, not necessarily having any symptoms, us not being able to detect when they've happened?

Peter - As you say, concussion may be so mild and transient that it may not even be picked up. You sometimes see that on the rugby field where somebody may or may not have a knock. They may be transiently dazed, but that can be quite a difficult diagnosis to make. Sometimes it is more obvious: there's a short period of loss of consciousness. Sometimes people have very few symptoms after a concussion. But classically, patients do have a number of symptoms. These can be what we call physical; so headaches, visual disturbance, dizziness, impairment, imbalance. They can be what we call psychological or cognitive; impairment of memory, impairment of concentration, thought processing and planning. And then quite challenging can be what we call the neuropsychiatric symptoms; changes in behaviour, the way we respond to others. And mood disturbance, particularly depression, can be quite a big problem for some of these patients.

James - What do we know about how neurodegenerative complications relate to traumatic brain injuries?

Peter - This is quite a difficult topic and something that we don't fully understand. There is a concern that particularly after multiple concussive injuries or even one severe traumatic brain injury, following the acute stage, that there is an impact on the brain in the longer term. So the risk of getting what we call neurodegenerative disease, probably the most cited is some form of dementia, but there are other complications such as seizures or even Parkinson's disease. And there's quite a lot of work going on now to try and relate that initial insult to these problems in life. The challenge is how do you do those studies? We can try and control people who've had brain injuries against the normal population and compare their brains, but in order to answer these questions accurately, we need to do what's called longitudinal studies where we need to follow patients who've had a brain injury for many, many decades, and those who haven't.

James - There are also genetic and lifestyle factors at play here. That's the difficulty with ensuring we're addressing the causation here rather than just a correlation?

Peter - Exactly. So just to break that down a little bit: the genetic makeup, our genes, do influence our outcome from brain injury. There is a sort of protein, lipoprotein E, and the type of this protein you have can influence how well you recover from injury. But in the longer term, I think some of the consequences, particularly professional people who play high level sport and then they suddenly stop playing it for whatever reason, maybe they've got another injury, has a profound effect on them because this is their wellbeing, this is their life. So whether that is a result of brain injuries or whether it's that dramatic change in lifestyle is something that we really need to try and get to the bottom of.

James - In that pursuit, do we have a good working hypothesis? People might be aware that dementia, Alzheimer's, it's because of this buildup of abnormal proteins in our brains. Do we have any guesses as to the mechanism through which traumatic brain injuries or even mild concussions lead to that?

Peter - So there's a number of studies trying to address the pathology and the pathophysiology of the link between the initial trauma and the dispositions in the brain later. But I don't think it's something that we do fully understand. And there probably is some population link between brain injury and these later problems. But of course, how do you relate that to each individual? And that's of course the challenge where you are trying to differentiate between population studies and what in effect is a case report for each individual patient.