Well I’ve read a few that talk about an association of low magnesium to hydrocephalus. This first one, in the British Medical Journal, talks about external hydrocephalus and hypomagnesaemia (and rapidly growing skulls in children):-
Others, such as the following one, talk about how treating hydrocephalus in rats using magnesium, offers mild benefit
A 1925 paper in The Journal of the American Medical Association, talks about how they successfully treated Intracranial Pressure with magnesium sulphate.
So, it’s not a new thing but it could be a promising thing.
There are however some reports that disagree with certain levels of magnesium being beneficial, so it needs looking at in depth.