Just a correction here -- the surgery is not considered high risk, but it is brain/skull surgery done in a very sensitive area and can have problems such as scar tissue formation over time afterwards and is not a cure -- it just halts progression. In at least around half of dogs, some symptoms return. That said, they do not generally seem to return to as bad a state as before the surgery. The morbidity rate is very low. A tiny number of dogs have problems right after. Some statistics are noted in Clare Rusbridge's FAQ.
Anyone releasing dogs from this surgery in less than three days should be viewed with scepticism IMHO. Many neuros keep them in 1-2 weeks or longer. The average seems about 10 days-two weeks. Younger dogs probably do better for the reasons Shannon noted but many dogs will not develop symptomatic syrinxes til older so there'd not really be a reason to consider surgery until then, IMHo but also I do think most neurologists also feel this way.
I personally would never bother with the worry or expense of MRIing a dog with no symptoms no matter the age, except for research.
Don't know the semantics of the difference -- all I was saying is what I noted already: he has all the typical signs of damage in the areas that are affected by SM. These tend to be motor function and various pain responses (the twisting to one side, the leg thumping without scratching anything, the attempt to scratch). It is very hard for neurologists to pinpoint exactly what is going on even from an MRI with this condition. I don't know if 'sensory neurons' are affected by SM as I have never heard a discussion of that context at any of the international symposia (nor from Clare Rusbridge). Or what the difference would be...? Pain is the main issue for these dogs and the motor problems/scratching,leg chewing/face rubbing/scoliosis etc are caused by pain and discomfort.The scratching is a motor neuron response not a sensory neuron response.
Unfortunately, vary little is understood about this condition in either humans or dogs. One of the leading human experts internationally attended one of the SM dog symposia I was at, and noted he'd spent his entire career trying to understand it and it remained an enigma after 40 years. So I don't think anyone can give any definite answers about what is being affected and why, best course of treatment etc. For all of us, and the neurologists, a lot of guesswork and crossed fingers are involved.