I can't find the link that i read earlier on the hydrocephalus question. Merc knows which one it is...... But i do know that hydrocephalus has been completely ruled out of this particular equation. Something to do with the internal structure of the cranium having the wrong surface. I think it was smooth whereas sufferers from hydrocephalus have a rough finish. Or something. I'll post the link when i find it again..
In the meantime have a look at this one