Gosh this is tough, I will give my 2c worth, but I am by no means an expert!
Did they do an MRI of your c-spine/neck too? Did they use gladolinium as enhancement? Hyperintense seems as if the lesions are enhancing with contrast, but you don't mention it specifically. What about an LP?
So you have 3 lesions in various areas in your brain. Peri-ventricular is one typical area for an ms lesion, but in terms of diagnostic criteria, you need more lesions, or some enhancing ones on the c-spine too, and/or more relapses.
Apparently, there are lots of folks walking around with some small 'spots' in their brains, but with no symptoms of any disease - this has been found coincidentally at autopsy. ON can have other causes too.
So the ON, and 'suggestion' of de-mylenation could indicate that you might end up with ms, or this could be a clinically isolated incident and won't recurr....
Horrible to be in limbo-land. Maybe you can spend a little time eucating yourself on ms symptoms so that you are aware of them. That way, if you experience anyof them, you can go straight back to the neuro, and if these new symptoms can be established clinically or on repeat MRI, you will fulfil the 'dissemination in time' criteria for diagnosis...
Hopefully, you won't experience any further relapses or new symptoms, and this is just a worrying glitch and you will continue with good health.
There is some good info here on diagnostic criteria - just do a search in the Forums - hope it helps.
So right now, they can't diagnose ms, and you may never have another problem, or you may end up developing ms - frustrating!
I do know that the trend now is to start using the CRABS early to treat clinically isolated syndromes, but they are horrible drugs and I don't know if I would want to be on them if I didn't have a definite diagnosis...
What kind of venous anomally are they talking about - I know it is a non-symptomatic and coincidental finding - just interested.
All the best for the future - hope the ON has resolved.