Replacing brain volume

In this column Cecil discusses what happens when surgeons remove part of the brain. In essence he is correct, the brain’s “natural juices” fill up the dead space. However, this rarely happens within the time frame of an operation. Instead, the space is irrigated with a saline solution approximating physiological parameters until the dura is closed, superiormost suture last, to minimise any retained air.

I understand the word “irrigated” to mean “washed” or “rinsed”. Are you saying the the empty space is filled with saline to occupy the empty space? That would make sense, but I want to make sure of what you mean.

Yes, you’re right. Sorry for the imprecision. During the surgery the brain is periodically washed or rinsed with saline to keep the tissues moist. This is called irrigation. It was the first term that came to mind. At the end of surgery the dead space is filled with saline, as you said.

Wait, wait - are you saying that neurosurgeons routinely engage in brainwashing?

/ducks and runs



Thanks for the clarification. So, the brain cavity is filled with saline and closed, then over time the saline is absorbed by the body as new “brain fluid” is made?

What is “brain fluid”? I realize there is liquid in the spinal column - that is what a spinal tap is getting. How much is there nominally?

The brain and spinal cord are bathed in cerebrospinal fluid (CSF) which basically acts as a cushion. It is produced within the ventricles of the brain continuously and is as continuously absorbed by the dura mater (the fibrous covering of the brain and spinal cord). In a normal state it is visually as clear as water. Total volume in an adult (with an intact brain) is about 150 ml. Daily production is around 500ml.

Excess production of CSF, or blockage of the outflow, is what leads to “water on the brain”, or hydrocephalus.

I understand that sometimes a whole cerebral hemisphere is removed (hemispherectomy). Apparently it is possible to get by with just one, and the results can be better in some circumstances than you get with leaving in a badly damaged hemisphere, which somehow"competes" with the good one.

In such a case, is it still sufficient to have the empty space filled with just liquid? I should have thought, when that much is taken out, the good hemisphere could flop about and get damaged further without something a bit more solid there to hold it in place.

Hemispherectomies were performed earlier in patients with intractable seizures who had in essence lost the use of one side of the body. Thus removing one half of the brain caused no further deficit and, as you say, protected the intact half from developing abnormal seizure activity. If done at a young enough age sometimes the non-functional half would regain some function.

The intact half of the brain is kept in position by a fibrous sickle-shaped structure running longitudinally between the hemispheres known as the Falx cerebri, as well as by the blood vessels running to it from the dura.

However, hemispherectomies did have the complication of blood vessels tearing possibly owing to excessive range of movement of the remaining brain, leading to collections of blood in the unoccupied cavity. The more modern procedure is a “functional hemispherectomy” or a hemispherotomy where certain important fibre bundles between the hemisphers are divided, leaving the bulk of the brain intact but with both sides unable to communicate (and thereby spread seizures).

By the way, your link didn’t work for me, so I hope we’re talking about the same thing.Added

Thanks, that is interesting. I have read quite a bit about neuroscience and neurology but I never heard of the Falx cerebri before.

Somehow an extra character crept in at the end of that link - this version should work - but it was not really intended for your benefit anyway, Damfino. Obviously you know a lot more about this than Wiki does. I just put it there for the benefit of other dopers who might be skeptical as to whether hemispherectomy was for real.

Damfino said:

So there is 300x turnover rate vs volume? That seems odd. That means over 3 times a day you get a full fluid change.

Thanks, njtt; that article was pretty accurate.

Irishman, yes, there is a 300% turnover rate within 24 hours. This is probably owing to the fact that the CSF also has waste disposal and metabolic functions in addition to its cushioning role.

Does that mean it’s part of how the blood/brain barrier works?

Yes, in a way. The CSF is created by filtration of blood through the choroid plexus of the ventricles. The same tight junctions of the endothelial cells of the blood vessels of the brain ensure that no large molecules enter the CSF, which is therefore typically described as “crystal clear” in a normal state. Certain waste products of brain metabolism pass through the BBB into the CSF and are later absorbed into the blood stream.