An MRI is a must to have because as previously mentioned it rules out other lager issues,, MS ,, tumors etc..
A Neuro should also do an MVA done at the same time as the MRI,,it's the contrasting part of the MRI. That shows the vascular system and can show a good Neuro a great deal. It can show if there is a clustering of blood vessels or a looping of vessels which can indicate a possible interaction of blood vessel and nerve.
However,, remember that it is not possible for any procedure to image a nerve. But with a good Neuro who has a lot of experience with TN,, they can infer from the MVA if there "might" be an interaction of blood vessel and nerve..
I went to an appointment a few years ago with a friend and the Neuro could clearly see a looping of vessels that should not have been there and said I think there is a good chance that here is where the problem is....he was correct and they did a very successful MVD...
So having an MRI is an essential first step in an accurate diagnosis of TN and in ruling out any other more serious problems...If you are afraid of having one (like me!!) make sure your MD is aware and they can medicate you so you will be more comfortable (or asleep) during the procedure.
Good Luck,, let us know what the results are.....Beth