Volumetric measurement of the posterior fossa and its components using magnetic resonance imaging in idiopathic trigeminal neuralgia

Background: The neurovascular conflict is now considered an unquestionable dogma in the pathophysiology of idiopathic trigeminal neuralgia (ITN). However, there are more and more papers that provide information about other factors that promote such conflict or neuralgia itself. AIMS. To measure the volume of the substructures of the posterior fossa in patients with ITN and controls and to investigate the association between a reduced volume of these structures and the incidence of ITN.

Methods: In 20 patients with unilateral ITN and 20 healthy participants, high resolution 1.5 T magnetic resonance imaging scans including axial and coronal sequences T2-weighted with a slice thickness of 1 mm were performed with the aim of a volumetric study of pontomesencephalic cistern, Meckel's cave and trigeminal nerve.

Results: Measuring the pontomesencephalic cistern on each side of the midline, the volume of the affected side cistern was significantly lower than the healthy side one in patients with ITN (p = 0.004) and also when compared with controls hemicisterns. No significant differences in the Meckel's cave nor the trigeminal nerve were found. The incidence of neurovascular conflict was also studied resulting in 10% of patients with ITN where the conflict was not identified.

Conclusions: Our data support the theory that a small volume of the posterior fossa cisterns containing the trigeminal nerve may increase the incidence of ITN.