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

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.To estimate morphological change in the trigeminal nerve after microvascular decompression (MVD).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.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).Morphological changes in the trigeminal nerve due to NVC could be recovered by MVD, and increases in the trigeminal nerve CSA predicted favorable outcomes.