Can an MRI scan diagnose trigeminal neuralgia?

The MRI scan is not necessarily and specifically intended to make the diagnosis of trigeminal neuralgia, because very often, the blood vessel causing the compression on the nerve is small enough that you can't see it clearly. Even patients with no facial pain often have blood vessels close to the trigeminal nerve, so it's difficult to make the diagnosis specifically by the MRI scan. It's not like a brain tumor, where the MRI scan makes the diagnosis.

The MRI scan is specifically intended to rule out other causes of facial pain, in some cases tumors. For example, a meningioma can cause facial pain. Blood vessel abnormalities like an arteriovenous malformation can also cause pain. Multiple sclerosis is one of the primary reasons that we do the MRI scan because multiple sclerosis will show up both in the cerebral hemispheres as well as the area of the brain stem and the trigeminal nerve. So if we see multiple sclerosis, then microvascular decompression is not the choice for the therapy. Specific therapy for the multiple sclerosis and symptomatic treatments are a better choice.