Role of the petrous ridge and angulation of the trigeminal nerve in the pathogenesis of trigeminal neuralgia, with implications for microvascular decompression.

INTRODUCTION

Vascular compression is the main pathogenetic factor in apparently primary trigeminal neuralgia; however some patients may present with clinically classical neuralgia but no vascular conflict on MRI or even at surgery. Several factors have been cited as alternative or supplementary factors that may cause neuralgia. This work focuses on the shape of the petrous ridge at the point of exit from the cavum trigeminus as well as the angulation of the nerve at this point.

METHODS

Patients with trigeminal neuralgia that had performed a complete imagery workup according to our protocol and had microvascular decompression were included as well as ten controls. In all subjects, the angle of the petrous ridge as well as the angle of the nerve on passing over the ridge were measured. These were compared from between the neuralgic and the non-neuralgic side and with the measures performed in controls.

RESULTS

In 42 patients, the bony angle of the petrous ridge was measured to be 86° on the neuralgic side, significantly more acute than that of controls (98°, p = 0.004) and with a trend to be more acute than the non-neuralgic side (90°, p = 0.06). The angle of the nerve on the side of the neuralgia was measured to be on average 141°, not significantly different either from the other side (144°, p = 0.2) or from controls (142°, p = 0.4). However, when taking into account the grade of the conflict, the angle was significantly more acute in patients with grade II/III conflict than on the contralateral side, especially when the superior cerebellar artery was the conflicting vessel.

CONCLUSION

This pilot study analyzes factors other than NVC that may contribute to the pathogenesis of the neuralgia. It appears that aggressive bony edges may contribute-at least indirectly-to the neuralgia. This should be considered for surgical indication and conduct of surgery when patients undergo MVD.