Persistent trigeminal artery: a rare cause of trigeminal neuralgia - MR imaging.

MR imaging (MRI) and MR Angiography (MRA) are useful in demonstrating vascular contact with trigeminal nerve at root entry zone (REZ) in-patients with trigeminal neuralgia. Often a tortuous, ectatic superior cerebellar artery, vertebro-basilar or elongated antero-inferior cerebellar artery causes compression at the REZ. Persistent trigeminal artery PTA (Primitive trigeminal artery) is a carotid basilar anastomotic vessel and documents itself in 0.02 to 0.6% of all cerebral angiograms. A 48 yrs old male, presented with persistent pain on right side of face, of 2 years duration. The pain had increased along the distribution of V-1 and V-2 division of trigeminal nerve for the last 6 months. On examination no neurological deficit could be elicited. MRI (Sagittal T1, Axial T1 and T2 wt. Fast spin echo and high-resolution 3D T1 weighted gradient echo sequences) and MRA (using 3D TOF technique) were performed on a 0.5 Tesla MR unit. Maximum intensity projection (MIP) in three standard planes axial, coronal and sagittal was generated. Thin slice reconstructed images were used to assess the fine anatomical relationship of the nerve and the vessels. MRI showed the origin of PTA to be arising from the postero­ lateral aspect of the posterior bend of cavernous segment (C4) of right internal carotid artery (ICA), coursed postero-laterally and inferiorly around the dorsum sella and communicated with basilar artery in the prepontine cistern [Figure 1]. In its lateral course, it compressed and distorted the REZ of right trigeminal nerve. As the patient was unwilling for micro-vascular decompression, he was treated conservatively with anti epileptic drugs.