In response to your question, "Can a migraine trigger a fever?", the answer is more than likely "No, it can't." Nothing about the (relatively poorly) understood physiological aspects of the HA would indicate a positive correlation with an increased body temperature.
However, if large amounts of caffeinated beverages or alcoholic beverages were ingested a few hours prior to the onset of the migraine, it's likely that the diuretic effects of caffeine and alcohol would result in dehydration, and being dehydrated will cause an increase in body temperature. Along the same lines, if nausea accompanied with severe vomiting had occurred a few hours prior to the onset of the migraine, again causing dehydration, a temperature spike may occur but not because of the migraine headache, itself. Ironically, the trigger for the migraine would also be the causal agent responsible for the 'fever'.
Anecdotally, I'm familiar with people "experiencing chills" as a symptom, but I've not heard about people feeling feverish. Do you feel the heat all over, or is it just around the head? Do you perspire; does it feel like a 'hot-flash' and ends quickly, or does the fever sensation last for the duration of the headache?
To GoneClimbing; very astute. It's a good move to document everything about your HAs. The more symptoms you can identify and are aware of, the better diagnosis your physician can provide, and the better treatment can be offered. I'm curious if you're male or female. What's the usual range for your temperature?
GizmoKat, I'm just willin' to bet that you're a female. Peri-menopause can hit anywhere between 35 - 55, and along with it comes a great fluctuation in body temperature throughout the 28 days of the menstrual cycle, as well as daytime versus nighttime. But if you could experiment and determine what your basal temperature variance is, and then compare that with your temperature at the onset of a migraine attack, that would be useful information for your physician. Will you see an actual increase in degrees, or will your results be similar to GoneClimbing's?
Lastly, I don't want to always be the voice of pessimism, but I wouldn't anticipate the MRI to yield much useful information. It’s just not a good diagnostic indicator of migraines. But an MRI can help eliminate other differential diagnosis your physician may be concerned about. Good luck, and please let me know what you learn about the temperature readings. I’m very interested in hearing back.