Steve, yes, really... a brain scan is the only definitive way in which PTSD can be 100% conclusively diagnosed. Sure, most psychiatrists, psycologists, therapists, etc can spot it a mile away if in full flight, being bad. The brain scan though is the only conclusive evidence that could ever be used in order to actually 100% say yes.

I think most has already been covered from others... and I think the neurologists needs to have a few more looks around, because whilst what you describe with the symptoms is PTSD, the other aspects as outlined already stands out that something is wrong within the brain still, or the knock has had more permanent effects than what they are telling / finding! Sure, time might be the only thing that can help you wife in regard to the other non-PTSD aspects, but atleast having a neurologist tell you that would be nice.