After a head injury, the brain does not sit still. It moves through phases, and each phase leaves a different signature.
In the first few days there is acute blood and swelling. By about thirty days that blood has converted to its chronic form. By ninety days the great majority of the volume change on the surface of the brain has already happened. Deeper structures keep changing for close to a year.
That timeline matters more than most people realize. A brain scanned in the swelling phase can look enlarged in the very region that was hurt. The same region scanned weeks later can look deceptively ordinary, because it has drifted back toward its old size before it begins to shrink.
So the question is never only what does the scan show. It is also when was it taken, and what should that phase look like.
Reading a brain injury well means reading the clock as carefully as the image.