Increase in Trigeminal Nerve Cross-Sectional Area on Immediate Postoperative MRI Predicts Favorable Outcome After Microvascular Decompression for Classical Trigeminal Neuralgia

BACKGROUND: Although distortion or indentation of a trigeminal nerve due to neurovascular compression (NVC) is associated with classical trigeminal neuralgia, whether morphological change in the trigeminal nerve is relieved by eliminating NVC has not been studied.OBJECTIVE: To estimate morphological change in the trigeminal nerve after microvascular decompression (MVD).METHODS: Fifty patients with classical trigeminal neuralgia who underwent MVD were included. Using coronal images in both preoperative and postoperative MRI, the trigeminal nerve cross-sectional area (CSA) was measured at 4 mm anterior to the nerve entry into the pons. Clinical outcomes were assessed using the Barrow Neurological Institute Pain Intensity Scale (BNI-PS) at the patient's latest follow-up.RESULTS: Forty-one patients achieved favorable outcomes without medication (BNI-PS I or II), and 9 patients had residual pain (BNI-PS >= 3A). The mean symptomatic trigeminal nerve CSA was increased by 51.47% after MVD in the favorable outcome group (preoperative: 4.37 +/- 1.64 mm(2) vs postoperative: 6.26 +/- 1.76 mm(2), P < .01), whereas it was not significantly changed in the unfavorable outcome group (preoperative: 4.20 +/- 1.19 mm(2) vs postoperative: 4.43 +/- 1.24 mm(2), P = .69). Kaplan-Meier survival analysis showed that the 3-year probability of maintaining a favorable outcome was 92.3 +/- 7.4% and 56.1 +/- 11.9%, for those whose symptomatic trigeminal nerve CSA was increased by over 20% and less than 20%, respectively (P < .01).CONCLUSION: Morphological changes in the trigeminal nerve due to NVC could be recovered by MVD, and increases in the trigeminal nerve CSA predicted favorable outcomes.