There is no specific test for trigeminal neuralgia. A diagnosis may be obtained by conducting a thorough medical exam and history of symptoms. Tests that may be useful to identify the cause of trigeminal neuralgia include a CAT scan or MRI. In approximately 80 percent of cases, MRI can detect whether a blood vessel is pressing on the trigeminal nerve. Unfortunately, not even MRIs can clearly diagnosis all causes of trigeminal neuralgia.