Cranial Nerve Tractography Contributes to Successful Skull Base Otoneurosurgeries

Background: Successful skull base otoneurosurgery also depends on the ability to preserve vasculonervous structures within the subarachnoid cisternae of the brainstem. At present, the anatomy of cranial nerves (CN) displaced by space occupying lesions in the cerebellopontine angle (CPA) is best delineated by dedicated tractography. We extend our previous reports on the clinical use of tractography. We compared the position of the CN by tractography and the interobserver variability with the in vivo location during otoneurosurgery. Methods: A clinical neurosurgery-ENT-neuroradiology team evaluated 24 patients aged 55 ± 14years (75% females) with mass lesions of the CPA (70% CNVIII-schwannomas). Standard MRI and tractography of the facial nerve (CNVII) was obtained in all the patients operated in Lisbon, Portugal. Results: With the exception of one patient, CN tractography was able to predict the course/displacement of the cisternal portion of CNVII, accordingly to the anatomic distortion found during surgeries. In a majority of cases (85%), CNVII was displaced either anteriorly, anteriorsuperior or anteriorinferior regarding the porus. Moreover, interobserver colocalization for each patient (PMGP vs. TT), showed a high level of agreement (R2=0.977; ICC = 0.98; p < 0.001). Conclusions: CN tractographies contribute to the successful skull base otoneurosurgeries, particularly by lowering the risk of CN injury during CPA surgeries and reducing the time spent to locate fiber bundles intraoperatively.