On many TN (Trigeminal neuralgia) forums, I came across a number of people having 2nd or 3rd MRI’s in order to obtain proof of a trigeminal compression. I did the same, had a total of 4 MRI’s and even drove hours to get to the latest model (Tesla 3). They never showed the compression that was found at surgery…
That is why I’m sharing the article below for it resumes what you should know about the role of the MRI in TN.
Should trigeminal neuralgia patients get neuroimaging? A neurosurgeon’s perspective
Mark E. Linskey, M.D.
Department of Neurological Surgery
University of California, Irvine Medical Center
Should patients with trigeminal neuralgia get neuroimaging usually in the form of MRI? Well, my answer to that is always yes but not for the reasons that are often thought. Many patients are told that what you’re looking for on the MRI is whether or not you have a blood vessel compressing the nerve and then if you find that there isn’t one there you’re not a candidate for microvascular decompression. Well, nothing can be further from the truth.
The main reason for getting the MRI is to rule out those 2-3% of cases where vascular compression is not the cause where you might have a tumor of the nerve or the brainstem. You might have a cyst in the cerebella pontine angle. You might have an aneurysm or an AVM and those require different treatments than treatment for trigeminal neuralgia. The trigeminal neuralgia there is secondary. You’re also looking for conditions that are very important for counseling patients for complication risk after surgery. Examples are patients who have Chiari malformations who have crowded steep angles in their posterior fossa. They have a much higher risk for hearing loss if they undergo microvascular decompression. Another example is a large vessel compression something we call a dolichoectatic vertebrobasilar compression. If you can say that ten times fast. But while the results of decompression for that are just as good for other blood vessels, the complication risk can be higher. We’ve published that result and it’s important to know that ahead of time to counsel patients.
The truth is that if a MRI scan shows a blood vessel there, that is a very important factor for predicting a potentially good outcome. But not showing a blood vessel there doesn’t mean anything. If you have the classic syndrome you will have the blood vessel there. The chances of finding it there in my series are at 100%. In a larger series of Dr. Jannetta’s it’s at 97% and the other 3% if followed over time turned out to be patients in the very early course of their MS and when followed longer were found to have MS later on.
The truth is that 2/3’s of patients have more than one blood vessel compressing and you only see that at surgery. MRI rarely shows more than one. So when it doesn’t show any, that doesn’t mean there isn’t a blood vessel there.
In scientific terms, we say that it’s positive predictive value is good, it’s negative predictive value is terrible, and it’s sensitivity is poor. So, be careful of that.
The other point I’ll make is that one of the tragedies of that misperception that is out there is that often a MRI that shows vascular compression is interpreted by a radiologist not used to interpreting that and then it gets into a MR report as a normal MR of the brain. A neurologist who may not be comfortable or a family practitioner or an internist who may not be comfortable reading the image themselves may see that and either delay or negate referral for a procedure that could be very helpful. If you’re going to even interpret the MR, it’s not the radiologist; it’s the neurosurgeon who’s experienced in interpreting this disease who needs to do the interpreting. And the technique of MR has to be very specific high quality, volume acquisitions, with very fine cuts.
Other info regarding MRI & TN :