Subha M, Arvind M. Role of Magnetic Resonance Imaging in Evaluation of Trigeminal Neuralgia with its Anatomical Correlation. Biomed Pharmacol J 2019;12(1).

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Manuscript received on :17-Jul-2018
Manuscript accepted on :07-Jan-2019
Published online on: 28-02-2019

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Second Review by: Exbrayat Jean-Marie
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M. Subha and M. Arvind

Department of Oral Medicine and Radiology Saveetha Dental College and Hospital Saveetha Institute of Medical and Technical Sciences Saveetha University. Chennai-600089 Tamil Nadu, India.

Corresponding Author E-mail: doctorsubha@gmail.com

DOI : https://dx.doi.org/10.13005/bpj/1640

Abstract

Neuropathic Pain is caused by a primary lesion or dysfunction of the peripheral or central nervous system. Trigeminal neuralgia is one such disease which is characterized by episodes of unilateral, lancinating, shock- like pains and are also intermixed with pain free episodes. It has a primary or classic and secondary type. Primary TN is due to neurovascular compression whereas secondary TN is due to any tumor in the brain stem. Trigeminal nerve has a sensory and motor root arising from the pons and travels to the face where it ends as three branches namely ophthalmic, maxillary and mandibular. Magnetic resonance Imaging is a gold in identifying these lesions. However, it is not always prescribed due to lack of insight in using MRI as an evaluating tool. It results in over dosage of medication as the physician prescribes the drug without identifying whether the lesion is primary or secondary. This article give an insight on the various MRI sequences imaged various studies available and also throws light on other sequence which has to be explored in this disease.

Keywords

Carmazepine; Magenetic Resonance Imaging; Oraofacial Pain; Trigeminal Neuralgia

Introduction

The International Association for the study of pain (IASP) defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. IASP in November 2010 further extended to define neuropathic pain as “Pain initiated or caused by primary lesion or dysfunction of the peripheral or central nervous system.¹ This is a modification of the previous definition of neuropathic pain which was described as “pain initiated or caused by a primary lesion, dysfunction, or transitory perturbation of the peripheral or central nervous system”.² When compared to nociceptive pain, the persistence of neuropathic pain is longer, not quite responsive to pain medications, often debilitating and difficult to treat.³ Neuropathic pain is frequent with other predisposing conditions like diabetes, carpal tunnel syndrome, sciatica, Guillain-Barre syndrome, cancer, multiple sclerosis, kidney disorders, alcoholism, HIV etc. The prevalence and incidence of neuropathic pain is estimated between 1 and 10%, with few studies admitted that neuropathic component may be present in 35% of all painful syndromes.⁴ Smith BH and co-workers stated that the estimate of prevalence tends to be lower (1-2%) than those based on classic symptoms reports.⁵ Gustorff et al. from their prospective survey in 2008 showed that in Austria the occurrence of neuropathic pain was 3.3%, with an increase in prevalence (up to 26%) as the age increases.⁶ Van Hecke et al. believed that due to lack of universal evidences and protocols, a range of incidence and prevalence rates has been identified. They also suggested that future epidemiological studies should take note of mentioned factors.⁷

Trigeminal Neuralgia (TN)

Trigeminal neuralgia (Tic douloureax), is a chronic pain affecting the Trigeminal nerve.  Burchiel KJ defined trigeminal neuropathic pain as constant unilateral facial pain that varies in intensity, is triggerable, and not curable.⁸ This is characterized by episodes of unilateral, lancinating, shock- like pains and are also intermixed with pain free episodes.

Clinical Features for Trigeminal Neuralgia

International Headache Society had recently proposed strict clinical criteria for trigeminal neuralgia diagnosis and according to this, diagnosis only can be made when there are at least three attacks of unilateral facial pain occur fulfilling the following criteria such as (1) occurring in one or more divisions of the trigeminal nerve, with no radiation beyond the trigeminal distribution and (2) pain with at least, recurring in paroxysmal attacks lasting from a fraction of second to 2 minutes or severe intensity or electric shock-like, shooting, stabbing, or sharp in quality or precipitated by innocuous stimuli to the affected side of the face.⁹ Eller JL and co-workers, in their new classification differentiated TN into type 1 and type 2 which was earlier referred as classic or typical TN and secondary TN respectively. Type 1 is characterized by episodic pain whereas type expresses as pain which more than 50% of the time is constant in nature.¹⁰ It also has been theorized that in type 2, there is likelihood to detect a structural abnormality such as tumours or vascular malformations.

Imaging Modalities in Evaluation of Trigeminal Neuragia

A wide variety of imaging modalities were used in past for image evaluation of the cranial nerves. Pneumocephalography was the first cross- sectional imaging study used to demonstrate cranial nerves. This technique involves introduction of air into subarachnoid space around cranial nerves in order to allow clear visualization of nerves within the basal cisterns.¹¹ Later, with advent of CT, the detail in visualizing the regions of cranial nerves has improved and further with injection of intrathecal contrast shows linear filling defects within subarachnoid space. But the visualization is limited to the cisternal or subarachnoid course of cranial nerves. But with advent of MRI, an imaging modality without using ionizing radiation and acquisition of multiple plane images it became standard mode of imaging of cranial nerves.¹²

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