Abstract
Two different clinical entities, essential or secondary neuralgia, are associated with different pathologies. The pathways of CN V comprise the cervical spine, the brainstem, the root of the nerve and the three peripheral branches: V1, V2, and V3. The lesions responsible for neuralgia are neoplastic, vascular, inflammatory, malformative or post-traumatic. The examination protocol should explore the set of CN V pathways. Neurovascular compression is the main cause of essential neuralgia. It is investigated by T2-weighted inframillimeteric volume. Two conditions are necessary to diagnose a neurovascular compression: localized on the root entry zone [(REZ), 2-6mm from the emergence of the pons] and perpendicularly. In the absence of neurovascular compression, thin slices and a gadolinium injection are necessary.

TAKE-HOME MESSAGES
• The range of pathologies responsible for trigeminal neuralgia is vast: neoplastic, vascular, inflammatory, malformative or post-traumatic.
• Two different clinical entities: essential or secondary neuralgia are associated with different pathologies.
• The possible topographical area affected is extensive from the cervical spine to the facial region.
• MRI investigation is based on an initial imaging protocol that can be completed by examination if lesions are detected.
• In this context, clinical understanding of the patient prior to the MRI scan is often a precious aid in directing the examination (essential or secondary neuralgia, affected dermatomes).
• In the case of essential neuralgia, the most commonly observed lesion is neurovascular compression. Diagnosis is based on T2  inframillimetric acquisition by visualising a vessel perpendicular to the REZ (at 2—6 mm from the emergence of the brainstem). 3D TOF then makes it possible to determine the arterial or venous origin of the compression.
• In the case of secondary neuralgia, good understanding of the anatomy of the CN V pathways is necessary.

Figure 11. Left neurovascular compression (arrow). Perpendicular vessel leading to pressure on the nerve on the zone corresponding to REZ (2 mm from the emergence of the brainstem).

Free Full Text https://linkinghub.elsevier.com/retrieve/pii/S2211-5684(13)00245-3