Is 90% of his brain actually missing or is the volume reduced by 90%? I.E. are the mass and connections still mostly there but just squished by extra fluid?
From what I can tell googling about this, it seems it is mostly just squished, so volume is down 90% but mass or neuron count is not missing 90%
I remember reading somewhere that they estimated he had 10-50 billion neurons, compared to the average of 86 billion, and they were squished into less than 15% of the normal volume.