Structural Magnetic Resonance Imaging Can Identify Trigeminal System Abnormalities in Classical Trigeminal Neuralgia

Abstract

Classical trigeminal neuralgia (TN) is a chronic pain disorder that has been described as one of the most severe pains one can suffer. The most prevalent theory of TN etiology is that the trigeminal nerve is compressed at the root entry zone (REZ) by blood vessels. However, there is significant evidence showing a lack of neurovascular compression (NVC) for many cases of classical TN. Furthermore, a considerable number of patients who are asymptomatic have MR evidence of NVC. Since there is no validated animal model that reproduces the clinical features of TN, our understanding of TN pathology mainly comes from biopsy studies that have limitations. Sophisticated structural MRI techniques including diffusion tensor imaging provide new opportunities to assess the trigeminal nerves and CNS to provide insight into TN etiology and pathogenesis. Specifically, studies have used high-resolution structural MRI methods to visualize patterns of trigeminal nerve-vessel relationships and to detect subtle pathological features at the trigeminal REZ. Structural MRI has also identified CNS abnormalities in cortical and subcortical gray matter and white matter and demonstrated that effective neurosurgical treatment for TN is associated with a reversal of specific nerve and brain abnormalities. In conclusion, this review highlights the advanced structural neuroimaging methods that are valuable tools to assess the trigeminal system in TN and may inform our current understanding of TN pathology. These methods may in the future have clinical utility for the development of neuroimaging-based biomarkers of TN.

Altered structure and functional connection in patients with classical trigeminal neuralgia

“…Smaller GM volume in patients of TN, as shown in this study, may represent an impaired ability in procession and modulation (loss of inhibition or altered thalamic firing) of neuropathic pain signals[Alshelh et al, ; Henderson et al, ]. On the other hand, central sensitization or use‐dependent synaptic plasticity can occur when there is the sustained or repetitive activation of nociceptive afferent fibers [DeSouza et al, ; Woolf, ]. The GM or neurons change the gain of their response to sensory input such that they have amplified responses to noxious stimuli.…”

Trigeminal neuralgia: An overview from pathophysiology to pharmacological treatments

“…[45][46][47] Notwithstanding this evidence, NVC can also be observed in asymptomatic patients. 48,49 Several alterations have been described as a result of the vascular compression, including focal demyelination at the entry zone of the trigeminal nerve, atrophy or hypertrophy of peripheral axons, and damage to Schwann cells as well as to peripheral myelin. [50][51][52][53] The "ignition hypothesis," proposed by Devor et al, 54 aims to correlate the structural changes with paroxysmal pain attacks, which are characteristic of the condition.…”

Biomarkers in temporomandibular disorder and trigeminal neuralgia: A conceptual framework for understanding chronic pain

“…In TN research, highresolution anatomical imaging (e.g., variations of T1-and T2-weighted images) assesses anatomical characteristics and patterns of neurovascular contact, brain gray matter volume, and cortical thickness, and diffusion imaging (e.g., diffusion-weighted images, diffusion tensor images [DTI]) assesses brain white matter and trigeminal nerve microstructure. 106 These advances in neuroimaging have already had significant practical implications in TN. Until recently, a central debate in our understanding of TN pathophysiology has been the degree to which neurovascular contact explains TN symptoms.…”

“…Although contact of the trigeminal nerve by an overlying blood vessel is one of the most common explanations for pain in TN, it has also been observed that neurovascular contact is not always present in patients diagnosed with TN. 106 Furthermore, contact of vessels with the trigeminal nerve can often be seen on routine biopsy and conventional MRI of asymptomatic individuals. 106 However, advanced imaging techniques have provided better resolution of the trigeminal nerve, demonstrating that although neurovascular contact may occur in asymptomatic trigeminal nerves, symptomatic trigeminal nerves are frequently dislocated or distorted by compressive vascular structures; furthermore, those changes correlate with TN symptom severity.…”