The big dark areas are just fluid. He had some kind of shunt to drain fluid from his brain as a child because of too much pressure. And sometime in the next 30 years there was a problem with the shunt failing, which caused fluid to back up. And the reservoirs of fliud known as ventricles basically grew extremely large from the increasing pressure and squashed his brain.

I don't have access to the article, is there any chance his brain might improve somewhat if the shunt was repaired?

They mention fixing things but the scores not improving. It is not clear to me if they theorise it will improve over time.