Ischemia can be caused by local infection, blood clot, athrosclerosis,or genetic abnormality in blood vessels. (or reaction to vaccine, usually live vaccine)
A severe herpatic infection can cause this too as well as meningitis.
Early, early m.s. can present this way, but generally MRI's are more specific to a certain region of spinal cord. It there is ischemia in white matter and not near scwann cells, this would indicate that it is not m.s. although M.S. has been seen in white matter before. Generally speaking with M.S. the ischemic regions are associated with swann cell nerves.
Since your venous studies came out normal it would appear you can rule out abnormalities in blood vessels and athrosclerosis.
If you throw tiny clots it is rare that they cause Ischemia in thoracic or cervical spinal cord. They usually end up somewhere else. So, it doesn't sound consistent with what usual findings are to have ischemia in white matter near a ventrical.
If you are concerned with clotting. Take baby aspirin daily. 81 mg only.
But it doesn't look like clots.
Generally, severe C.N.S. involvement can happen in herpatic diseases. Once fought off they stay pretty dormant in nervous system. But remaining scar tissue can be a pain. So, if you did have an extensive herpatic outbreak, this could account for what you are seeing today.
Other viruses that can cause what you are seeing are the meningitis viruses.
Guilliam Barre virus.
But for these virus to leave ischemia near ventricals is rare as meningitis virus targets a lining in the brain, guilliam barre target swann cells just like M.S.
There is some new argument that mycobacterium can cause this too and even fungus, but fungal infections are rare in nervous system, although by Grandfather had fungal tumor near his pituitary. He had brain surgery at 82 years old.
A second opinion is never a bad idea. The problem with second opinions is that if you ask your insurance company or doctor for one,....they will refer you to a doctor who will not contradict existing doctors.
Second opinions are better if you seek out another neurologist yourself. Make sure they are not on same HMO. Pay for it yourself but get prior authorization through your insurance so that you can bill them for it and seek reimbursement.
Things that may help these head aches are:
1) increased oxygen
2) low dose anti-inflamatories taken with food and buffers on regular schedule.
3)Ginko biloba in timed release capsules.
If your headaches start in back of neck, try very hot showers followed by cold to neck. May alternative like this for as long as you need.
If you feel your symptoms are progressing, see anti viral protocols and consider some of them.
Good Luck
Bret