MRI in Trigeminal Neuralgia

Trigeminal neuralgia is one of the most severe chronic pains in human .The dominant theory of in trigeminal neuralgia etiology is compression of cisternal segment of trigeminal nerve by neighbor blood vessels .In addition there are other lesions along nerve from nerve nucleus to distal branches that can cause pain such as demyelinating plaques , tumors and etc .High resolution MRI ( CISS and T2 space sequences ) is considered the optimal method for evaluation of suspicious patients to trigeminal neuralgia .-Exact etiology of TN remains unknown but the most common theory is compression of the root entry zone of nerve by blood vessels.-Several studies demonstrate pathologic changes specially demyelinating of the nerve at the contact point and sensory impulse from demyelinating region or spontaneous activation of injured neurons . .- Vascular compression may be seen anywhere along the cisternal segment of nerve but dorsal root entry zone which is covered by central myelin is thought to be the most sensitive portion due to thinner central myelin sheet in compare to peripheral myelin.-Length of REZ varies between patients and can extend to pours trigeminus.-We divided relation of vessels and nerve into 3 categories:1. Contact of nerve and artery with obliteration of intervening CSF.2. Compression of nerve without displacement.3. Displacement of nerve.Protocol and interpretation :- At our department , patient suspicious to trigeminal neuralgia undergo MRI study with thin slice multiplanar heavily T2 sequences , CISS ( constructive interference steady state ) and T2 space sequence , so multiplanar reformats in any planes is possible .- In addition, routine whole brain study with FLAIR sequences to identify probable plaques and tumors is done.Interpretation should be adopted to neurosurgeon needs, identifying compressive artery or vein, place of compression , degree of contact. Conclusion : - Imaging has become very important in selecting surgery candidates in trigeminal neuralgia. If no contact is detected, surgery for decompression is questionable. - Adequate imaging protocols and familiarly of radiologists with the appearance of vascular compression can reduce the number of unnecessary operations .