Xray is not the current diagnostic tool for looking at your brain, more so your skull. And not every person with TN has it show up on an MRI, even though it may be there, although some do.
Here is a link for good visuals of brains and explanations of the different diagnostic scans like MRI's, PET, and CTs.
Yes, your brain anatomy can be visualized on an MRI scan. A CAT scan can visualize skull fractures, tumors, etc., but an MRI shows your underlying vascular structures of the brain.
I, too, have suffered with trigeminal neuralgia, which has been controlled with Neurontin and also steroid injection blocks in head and neck.
I hope this has been of some help to you.....Take care.....