My Brother Had Surgery On His Brain Due To An

My brother had surgery on his brain due to an accident about 5 yrs ago. They had to remove the skull bone flap and it was out and put in a refrigerator for 6 months for swelling to go down. They put it back in but now it is like it did not fuse back together. He recently had a CT scan and it is showing large parts of his brain that are exposed and I am wondering what the best thing to do would be to move forward so his brain is not exposed like it is. Can they use plates or fillers or what??