This disease occurs because of the improper CSF volume, we can describe it as a big sized head for new born babies. Excess accumulation of CSF (increased volume) , brain volume increased and then head volume increase. You should ask how head volume will increase and the brain is surrounded by a bony structure? The answer is in new born babies the junctions between bones are not tightly closed so it is still flexible , according to that skull bones will depart from each other.