Massive Ventricles

 From article in The Lancet 2007 titled 'Brain of a white-collar worker' 

A 44 year old man presented to the doctor with a weakness in his leg. 'His neurological development and medical history were otherwise normal. He was a married father of two children, and worked as a civil servant.' On CT scan they found an incredible brain that is mostly ventricles. 

Wild, how does that work? 

 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61127-1/fulltext