Validation and evaluation of the volumetric measurement of cerebellopontine angle cistern as a prognostic factor of microvascular decompression for primary trigeminal neuralgia

The aim of this study was to analyze the prognostic factors of trigeminal neuralgia (TN) after microvascular decompression (MVD), and to evaluate the volumetric parameters of the cerebellopontine angle (CPA) cistern as a pathogenic factor and imaging predictor. This retrospective study included 70 patients with primary TN treated with pure MVD, followed up for at least 1 year and evaluated by high-resolution MR imaging. The volume of the CPA cistern was calculated bilaterally, and the "Cistern Deviation Index" was defined to represent degree of deviation of the CPA cistern. Clinical data and volumetric parameters were compared between patients with TN and age- and sex-matched controls without TN, and between the recurrent and non-recurrent patients. The transposition procedure had a better outcome than the interposition procedure (P < 0.001). There was a significant difference in the volume of CPA cistern between the affected and unaffected side (152.1 +/- 50.1 vs. 179.9 +/- 63.7 mm(3), P < 0.001) in patients with TN, while no significant difference between the right and left side (158.7 +/- 44.6 vs. 163.1 +/- 49.8 mm(3), P = 0.162) in controls. The Cistern Deviation Index was significantly larger in controls than in patients with TN (P = 0.048), and in the non-recurrent patients than in recurrent patients (P = 0.040). We demonstrated that the volumetric parameters of the CPA cistern are a marker for understanding the pathogenesis of TN and useful for predicting the recurrence after MVD. The Cistern Deviation Index might contribute to deciding the surgical approach.