Welcome to the board, Sue. It is a progressive condition and dogs need to be at least 2.5 to be given a grade on the grading programme. While an early scan gives a good indication for many dogs of where they might be heading, it won't guarantee an A dog, for example. Most neurologists familiar with scanning over time will be pretty good at estimating whether a scan shows reason to be concerned or not, on a dog under the grading age. Most in my experience will give some sort of general prognosis. AxA matings won;t guarantee clear dogs either, though the statistics are considerably higher. Non A dogs in matings have as far as I know yet to produce a single A offspring. But A to D produces very good results, too and for genetic diversity and to retain other good genes, breeders will need to use Ds too. Ideally more dogs will be scanned so more breeders will know of more A options.
The older the dog at the time of scan and breeding, the better with progressive conditions.
I recently had all four of my dogs scanned -- two are rescans of dogs first done at just over a year, which are now about to turn 5.
I haven't yet had time to post on my experience because I wanted to get pictures that I can post, so that people can see the scans and what they mean.
On his original scan in 2005, Leo, my dog with SM, was showing herniation, dilated ventricles, a kinked spinal cord and a small syrinx when totally asymptomatic at age 1 year 5 months. He was symptomatic, mildly, by age 2.5. Now he is moderately symptomatic, scratching and some tenderness on and off. His rescan showed his syrinx had not grown in length (it is quite short) but has widened quite a bit (width is the predictor of pain) and is now graded large. His ventricles remained the same. Jaspar, who was clear then for everything except perhaps some hind brain compression in 2005, remains without a syrinx and is confirmed as an A graded dog now that he is over 2.5. He has slightly enlarged ventricles now (the meaning of enlarged ventricles remains unknown -- some breeds naturally have very large ventricles -- but the size is recorded for scans).
Of my other two, Lily my rescue scanned with SM as I had expected -- the reason I never homed her (I run a rescue) was because she already had some suspicious scratching when she came in. If you have had a dog with SM and seen the difference in scratching you tend to know when it is a bit less likely to be 'normal scratching'. On the plus side, her scan was much better than I had guessed it would be (I stress again I was expecting this result; my concern was not that it would show SM but what the scan would show overall as to where she is now). Her syrinx is tiny and as she is three or four I wouldn't expect it to get a lot worse. :xfngr: It is important to stress that many of our dogs live with syrinxes all their lives and are easily managed; many will never require any treatment and we won't even know they have a problem because most of us do not scan our pet cavaliers. But breeding unscanned asymptomatic dogs is in my opinion another issue -- if my breeder had his original choice, Leo would have been bred at the time he was asymptomatic and if I hadn't scanned I'd never have known the difference. I also think his symptoms would not have been seen as a kennel dog in a breeding programme or even if he had been shown or lived indoors with a group of dogs by someone not looking for signs, probably til he was closer to 4-5).
Lucy, I am delighted to say, a 9 year old dog bred by Laura Lang of Roycroft Cavaliers in the US, had a superb scan -- clear of everything! Interestingly this result was predicted by some researchers, and I know confirms Laura's own theories about lines and selecting certain lines for health and she is a real tribute to her breeding programme in both health and personality. Lucy's scan was valuable for researchers who have few scans on older dogs. Lucy was totally clear for PSOM too.
I hope those details may give some insight.
When I get a chance I will do a detailed post on my trip and get up some images of the scans.