Response by the Authors of Original Article

In Response to “Facial Nerve Schwannomas Mimicking as Vestibular Schwannomas” by Beth N. McNulty et al

We would like to thank the authors of the letter to the editor regarding this study for calling attention to an additional imaging modality that may aid in distinguishing between tumors of facial nerve origin and vestibular schwannomas. The objective of our study was to identify both preoperative and intraoperative tools to better distinguish facial schwannomas from vestibular schwannomas. The authors suggested that diffusion tensor tractography may be used to establish a relationship between facial nerve fibers and tumor. It was asked that we clarify the imaging protocol for our institution. The patients, in this study, were evaluated using our institutional imaging protocol of preoperative magnetic resonance imaging with and without gadolinium contrast. We do not employ intraoperative neuronavigation in these cases. The authors quote two studies that have shown diffusion tensor tractography to be valuable in predicting the location of the facial nerve in relation to the tumor.[1] [2] While this imaging tool is gaining popularity among skull base surgeons, a recent systematic review found only 14 studies documenting its use in vestibular schwannoma resection. The review concluded that it is indeed a useful adjunct in large vestibular schwannomas, size > 2.5 cm, successfully identifying the facial nerve course in 96.6% of tumors with an accuracy of 90.6%[3]. We agree that this may be a useful tool in the future but recognize that ongoing research is needed to evaluate the cost-effectiveness and to further establish a direct benefit to facial nerve outcome with its use.

• References

• 1 Chen DQ, Quan J, Guha A, Tymianski M, Mikulis D, Hodaie M. Three-dimensional in vivo modeling of vestibular schwannomas and surrounding cranial nerves with diffusion imaging tractography. Neurosurgery 2011; 68 (04) 1077-1083
• 2 Yoshino M, Kin T, Ito A. , et al. Feasibility of diffusion tensor tractography for preoperative prediction of the location of the facial and vestibulocochlear nerves in relation to vestibular schwannoma. ActaNeurochir (Wien) 2015; 157 (06) 939-946 , discussion 946
• 3 Savardekar AR, Patra DP, Thakur JD. , et al. Preoperative diffusion tensor imaging-fiber tracking for facial nerve identification in vestibular schwannoma: a systematic review on its evolution and current status with a pooled data analysis of surgical concordance rates. Neurosurg Focus 2018; 44 (03) E5