What keeps the brain in place after a hemispherectomy?

03 October 2010

Question

Hello, Chris and company, love the show. I've read that the human brain has a very gelatin-like consistency. I also heard you talking last week about people who have had a hemisphere of their brain removed. This makes me wonder how they keep the rest of their brain from oozing all around the inside of their skull. It seems like if they were in a car that stopped short or just shook their head too quickly, things would fall apart, no? Do the doctors fill the empty part of the skull with something? The medical equivalent of foam packing peanuts? Actual packing peanuts?

Answer

If you look at what brain tissue is like, it is very soft and floppy. It's almost like blancmange, the consistency of fresh brain tissue. You're right that when someone actually has to have a portion of their brain removed, it would leave a very big space because the volume of an adult human brain is about 1.5 to 1.3 litres, 1300 centimetres cubed. So it's quite big and if you removed half of that from your head, then you'd obviously have a space which is about 700 ml of empty space. Now people did originally worry that there might be a problem with what to do with this empty space inside the head of someone who's had half of the brain removed. Let's just revise why people might have that done. If you have got some kind of problem for instance intractable epilepsy of which this was performed quite often in the past, relatively speaking especially in young children for which their recovery actually is really good. They get back pretty normal life actually, after having this done. It sounds pretty draconian, but it works very well. What you then end up with is a space in the head and you've got to fill it with something. Well, people did worry that this would be a problem but what they discovered in the long term is that in fact, it fills up with cerebrospinal fluid, the same stuff that bathes the brain and spinal cord anyway and there doesn't seem to be a major problem. The brain is quite well supported inside the head and although it is floating in this bath of CSF (Cerebrospinal Fluid), actually, there are various supporting structures which help to hold the brain in one position. And going from front to back, so if you imagine if you had your fingers in the middle of your forehead and you ran your fingers backwards vertically over the top of your head towards the middle of the back of your head, there is a piece of tissue called the falx cerebri which inside your skull follows a sort of similar course to that, and that holds your brain in and stops it going from side to side.

At the back of the head there is also a structure called the tentorium cerebelli which is a horizontal piece of tissue which holds the brain vertically and there's also the main meninges which go around the brain and they provide a degree of support as well. So it turns out that there's not a major problem because the kind of movements you would have to make to make your brain go from side to side would be so severe that you'd probably be damaging yourself quite seriously anyway. So actually, as it turns out, it hasn't really become a major problem for people who have had this hemispherectomies.

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