Human beings have large heads compared to other animals. This is one of the reasons human babies need to be born well before reaching brain maturity or otherwise they will get stuck and never come out!
In anthropology, when you get a skull of a human and you need to know how much this person’s brain reached, scientists simply fill the cavity of the skull with a certain fluid substance and then get the volume of the fluid. The volume inside the skull is a fingerprint of the brain’s largest size during a lifetime.
High field MRI scanners (ideally 1.5 or 3 Tesla) together with mathematical computer algorithms can do the job of a hard-working anthropologist but in an oviously safer in-vivo way than to fill a person’s skull with fluid.
Brain Tissue Reserve (MLBG)
Using a high resolution T1 MRI sequence, you can simply measure the volume of the entire intra-cranial (Skull) cavity as well as the brain size.
The full-sized brain will occupy the whole intracranial cavity, which is termed “Maximal lifetime brain growth” (MLBG). If the brain loses some of its cells and fibres then its volume will shrink from the full-sized MLBG. After reaching our full-sized brain, we normally lose some volume (~0.4%) annually. This rate accelerates in many neurological conditions and MS is a classical example for that.
MLBG is very informative measure and may well guide individualized MS care. Sumowski et. al, showed that patients with MS (PWMS) who had larger MLBG can withstand cognitive decline compared to lower values. Larger MLBG indicates more brain tissue that can compensate for damage before burn out eventually.
This concept is termed “Brain Tissue Reserve” in analogy to the term “cognitive reserve” which is the rich intellectual attainment for every one of us. Both reserves help us withstand any degenerative or a destructive process that may take place in our brains.
Intellectual enrichment in PWMS showed a moderating effect similar to larger MLBG on cognition in the same study.
In clinical practice, if we can get an estimate of MLBG early after diagnosis, we may be able to direct specialized care to those who are at increased risk of cognitive affection.
Brain Volume at MS onset may tell the story before it starts
But one other point that impresses me even more about MLBG. Using MLBG, I can compare my today’s brain to my largest brain volume that used to occupy the whole skull cavity.
We now know that MS damage starts well before onset of first symptom, and at the moment we confirms MS diagnosis the brain suffers years of volume change.
Comparing MS brain volume on diagnosis to its MLBG may give an idea about how fast/severe is MS damage over the period preceeding diagnosis.
In fact other factors might be affecting the degree of this atrophy such as environmental toxins or smoking (among many others), but it remains that if brain atrophy is significant, then there is a loss of tissue reserve and probably ability to compensate for further MS damage. This should alerts using an effective therapy for this patient population.
Brain atrophy on first presentation of MS has been always associated with wors long-term outcome.
PWMS who had higher rate of brain volume loss at their first year of diagnosis have worse outcome compared to others.
We can simply have a look into the future by looking back into the past.
Why brain volume is not widely available?
There are plenty of technical and resource kind of problems that make it not widely available, but one major conceptual difficulty still outstanding.
We have no universal reference values for what is normal and what it abnormal in brain volumes. In other words, it is difficult to compare one brain to another.
Brain volume is quite variable between individuals, geographical regions, ethnicities, and even within the same person (your brain volume is different before and after drinking a lot of water for example).
If your brain should be compared to another brain, then it is the best to be your very same brain at a different time point.
Most neuroimaging research has been focusing on comparing your today’s brain to your future brain on follow up. Two brain scans, one year apart, and then calculate the rate of change between the two scans. This is termed the percentage brain volume change (PBVC), and by far this is the most reliable way to measure brain volume change.
If we compare the today’s brain size to its MLBG (the past brain), we may be getting an idea on aggressivenss of MS damage on an individual level, and be able to direct better theraputic options earlier.