We all have ventricles, sort of cavenous like spaces filled with spinal fluid in the middle of the brain. They enlarge as brain tissue is lost or if there is a blockage and they fill up,,hydrocephalus. You have seen babies with big heads, or used to, now they shunt the fluid off and the babies heads don't get huge. Big ventricles occur as we age. Other conditions cause them. I can't tell much about the cortex but it looks small to me but not gone. Just smaller. If you have a stroke, one part will get small. This looks just generally smaller but there is a cortex. It isn't all gone.
I went to school with a hydrocephalic boy who was also a dwarf.
His head was -huge- and he graduated at the top of his class and was always on the honor roll.
Apparently the brain can always find another way....:)