I think they avoid doing contrast MRIs, if possible because a) they're more expensive and b) there is a potential for the patient to be allergic to the dye. Both my mother and mil have had reactions to the contrast dye, my Mum knew she was allergic to seafood, which is apparently a component but they forgot to inform her of that. Mil has never been allergic to anything, but still had a scary reaction to it.
I was pretty sure it wasn't MS in my case anyway, as the location of the lesions was too diffuse and although there were some close to the MS pattern, none of them seemed typical enough to me. I do think mine are down to either migraine or cerebral hypoxia:
"The brain requires approximately 3.3 ml of oxygenated blood per 100 g of brain tissue per minute. Initially the body responds to lowered blood oxygen by redirecting blood to the brain and increasing cerebral blood flow. Blood flow may increase up to twice the normal flow but no more. If the increased blood flow is sufficient to supply the brain’s oxygen needs then no symptoms will result.[6]
However, if blood flow cannot be increased or if doubled blood flow does not correct the problem, symptoms of cerebral hypoxia will begin to appear. Mild symptoms include difficulties with complex learning tasks and reductions in short-term memory. If oxygen deprivation continues, cognitive disturbances, and decreased motor control will result.[6] The skin may also appear bluish (cyanosis) and heart rate increases. Continued oxygen deprivation results in fainting, long-term loss of consciousness, coma, seizures, cessation of brain stem reflexes, and brain death.[7]"
Sounds suspiciously like POTs to me, although obviously with POTs, as soon as you collapse or lie down the hypoxic episode ends, so there's no danger of it progressing to coma or brain death etc.
My big blackouts in 2012 (two back to back) involved seizure-like jerking and were mistaken for seizures by the Acute Medical Unit at the hospital. I assume this was due to prolonged hypoxia. I don't know if any of my previous blackouts included the jerking, as typically, I was alone for quite a few of the worst ones and not near anything that would cause bruising. The 2012 ones were in a very fancy hotel bathroom, with antique furniture like chairs and wash-stands. I was black and blue after those ones. Fortunately I haven't blacked out since and we think we know what precipitated them, so I won't be repeating the experience.