You all mean hemiplegic migraine I assume?
I too suffer from severe Hemorrhagic migraines. I have had a CVA in 2009 and in 2010 in which my Neurologist was able to witness one of my attacks in person and at that time put me on Toparimate 150mg(once a day) and Max Alt 10mg (as needed) for the headaches. It was helping for a while until just this past month I was rush to the hospital once again. I had several CT SCAN's, MRA's, MRI's, & EEG's. They now have increased my Toparimate to the max to see if it will help with the headaches. What happens is the vessels in the brain constrict causing lack of blood flow and oxygen to the brain and body, then it releases causing the stroke like symptoms (this also depends how long it constricts). Mine constricts for a long time. Headaches are coming on more each week, about 5 a week. Now after the last event, I have constant throb or dull numbness upon my head. Ask your doctor for a EEG, MRA, CT SCAN. then ask about Toparimate (Topamax) start out in small dosage 50mg and work up as you need it. I hope this help you from one suffer to another.
I hope that someone else can provide you more info. I have spent time trying to research it on-line, but didn't find out much except that there appears to be different kinds and causes of it. BTW, it is spelled "hemorrhagic migraine". You might spend more time to find out more about it on-line, but the very best thing to do is to get more information about it from your doctor who will know about your particular case. Your doctor is probably waiting to see what the MRI shows before going into it further with you. Hope that you can get the MRI soon. Good luck.