Analysis of the Sensitivity and Specificity of Magnetic Resonance Imaging for the Diagnosis of Trigeminal Neuralgia

Introduction: The most common cause of trigeminal neuralgia is the compression of the root of the trigeminal nerve by a blood vessel at the level of the pons. This can sometimes be demonstrated through MRI; nevertheless, the reliability of this study has been questioned by several studies.

The meta-analysis published by Antonini et al demonstrated that the sensibility of this test published along various studies is highly variable. According to this study, when the neurovascular contact is localized to the proximal root entry zone of the nerve and nerve atrophy is present the specificity of the test is elevated to 100%; however, the sensibility remains at around 52%. Similar studies have shown that up to 50% of healthy people can have unilateral or bilateral neurovascular compression of the nerve in an MRI without ever showing clinical signs of trigeminal neuralgia.

The treatment of choice in patients with classical trigeminal neuralgia with refractory pain is Microvascular Decompression. The newest classification published by the American Academy of Neurology in 2016 proposes that for a patient to be candidate for this surgical treatment one must demonstrate the presence of neurovascular contact through MRI. But since there appears to be a low capacity of the test to diagnose the presence of neurovascular compression, a proportion of the patients might be deprived of the possibility of receiving a life-changing treatment that can alleviate their pain and improve his quality of life. Based in the experience at our center, many patients with refractory pain that do not present alterations in the MRI and that undergo microvascular decompression surgery end up showing an underlying neurovascular contact during the operation.

Methods: All patients with diagnosis clinically established trigeminal neuralgia seen at our center that had an MRI because of their symptoms and underwent microvascular decompression surgery between 2014 and 2017 were included.

Two expert radiologist blinded at the final diagnosis analyzed the MRIs searching for the presence of neurovascular contact and trying to diagnose the side of the face affected in each patient. Cases of bilateral trigeminal neuralgia were excluded from the final analysis. The radiologists also detailed some characteristics of the neurovascular contact such as, location of the contact based on the REZ or non-REZ, location base on thirds, nerve thickness, nature of contact, presence of atrophy, intensity, displacing, unraveling or flattening of the nerve.

Results: Sensibility ranged from 54.8 to 57.1% and specificity of 76.7 to 76.9% in both observers. There was a statistically significant difference among the observations from both radiologists regarding the classification of the contact by REZ/non-REZ. Classifying the NVC by thirds appeared to have more congruence between them. The anatomical changes of the trigeminal nerve were observed in a minor proportion of patients.

Conclusion: The MRI demonstrated a sensibility of 54.8 to 57.1% for the diagnosis of trigeminal neuralgia in our study and a specificity of 76.7 to 76.9%. The MRI can aid in diagnosis and planning of the surgery; however, it should not be a guideline for determining the type of treatment that a patient is to receive.

No conflict of interest has been declared by the author(s).