Letter to the Editor Predicting Shape, Location, and Course of Facial Nerve in Relation to Large Vestibular Schwannoma on Diffusion Tensor Imaging with Intraoperative Correlation: Important Surgical Adjunct
LETTER: he article by Zhang et al.,1 entitled “Preoperative Prediction of Location and Shape of Facial Nerve in Patients with Large Vestibular Schwannomas Using Diffusion Tensor ImagingeBased Fiber Tracking,” published recently in WORLD NEUROSURGERY, was read with great interest. The facial and vestibulocochlear nerve complex occupies a different position and course in relation to the larger vestibular schwannoma and shows morphologic alteration by compression effects, displacement, and varied degrees of adherence to the capsule of schwannomas. Zhang et al. analyzed variations in the position and morphology of facial nerves on diffusion tensor imaging (DTI)ebased fiber tracking in the preoperative phase and correlated them with intraoperative microscopic findings as well as electrophysiologic monitoring and verification in 30 cases of large vestibular schwannomas. Preoperative DTI visualization of the facial nerve was successful in all cases and correlated well with the cisternal segment location of facial nerve during intraoperative observation in the 96.7% cases with good reproducibility and reliability; additionally, DTI showed moderate ability to distinguish morphologic changes between thin and compact varieties of facial nerves. Zhang et al. also determined the appropriate setting for facial nerve DTI fiber tracking.
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Apart from location, morphologic alteration of facial nerves plays an important role intraoperatively, and prior knowledge of such change is definitely likely to further increase the chance of anatomic as well as functional preservation of facial nerves. Zhang et al.1 attempted to correlate the morphology of facial nerves by categorically dividing facial nerves into compact and flat varieties. In 2015, Yoshino et al.2 advocated combined use of diffusion tensor tractography and multifused contrast-enhanced fast imaging employing steady-state acquisition for prediction of the positions of facial and cochlear nerves in relation to vestibular schwannoma. Gerganov et al.3 classified the morphologic changes of facial nerves caused by large vestibular schwannomas into 2 varieties: compact and flat like an umbrella or lying splayed on the
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surface of the schwannoma. These authors further noted that DTI study findings failed to predict morphologic changes of facial nerves as a result of pressure effects of large vestibular schwannomas.3 Song et al.4 categorized facial nerve morphologic changes into 3 different categories: 1) wrapped in the arachnoid membrane, 2) parallel, or 3) adherent. They found no association between shape of the reconstructed DTI fiber bundles and the intraoperatively observed actual shape of the facial nerve. The study by Zhang et al.1 has a few concerns. First is the limited potential of DTI fiber tracking to distinguish the facial nerve from the vestibulocochlear nerve complex. Second, Zhang et al. categorized morphologic alterations of facial nerve into simple compact and flat types, but in reality different variations are reported based on assessment of the intraoperative phase. Finally, manual tracking results are highly dependent on the user and can be a biased factor affecting accuracy and utility of these imaging findings. Despite these concerns, Zhang et al. provide an important observation that can be used in the future for navigation guidance of facial nerve during microsurgical excision of large vestibular schwannomas. This will definitely further improve the feasibility of anatomic and functional preservation of the facial nerve and likely improve the confidence of neurosurgical team. Guru Dutta Satyarthee Department of Neurosurgery, Neurosciences Center, AIIMS New Delhi, New Delhi, India To whom correspondence should be addressed: Guru Dutta Satyarthee, M.Ch. [E-mail: [email protected]] http://dx.doi.org/10.1016/j.wneu.2017.04.039.
REFERENCES 1. Zhang Y, Mao Z, Wei P, Jin Y, Ma L, Zhang J, et al. Preoperative prediction of location and shape of facial nerve in patients with large vestibular schwannomas using diffusion tensor imaging-based fiber tracking. World Neurosurg. 2017;99: 70-78. 2. Yoshino M, Kin T, Ito A, Saito T, Nakagawa D, Ino K, et al. Combined use of diffusion tensor tractography and multifused contrast-enhanced FIESTA for predicting facial and cochlear nerve positions in relation to vestibular schwannoma. J Neurosurg. 2015;123:1480-1488. 3. Gerganov VM, Giordano M, Samii M, Samii A. Diffusion tensor imaging-based fiber tracking for prediction of the position of the facial nerve in relation to large vestibular schwannomas. J Neurosurg. 2011;115:1087-1093. 4. Song F, Hou Y, Sun G, Chen X, Xu B, Huang JH, et al. In vivo visualization of the facial nerve in patients with acoustic neuroma using diffusion tensor imagingbased fiber tracking. J Neurosurg. 2011;115:1087-1093.
105: 1002, SEPTEMBER 2017 WORLD NEUROSURGERY
LETTER: he article by Zhang et al.,1 entitled “Preoperative Prediction of Location and Shape of Facial Nerve in Patients with Large Vestibular Schwannomas Using Diffusion Tensor ImagingeBased Fiber Tracking,” published recently in WORLD NEUROSURGERY, was read with great interest. The facial and vestibulocochlear nerve complex occupies a different position and course in relation to the larger vestibular schwannoma and shows morphologic alteration by compression effects, displacement, and varied degrees of adherence to the capsule of schwannomas. Zhang et al. analyzed variations in the position and morphology of facial nerves on diffusion tensor imaging (DTI)ebased fiber tracking in the preoperative phase and correlated them with intraoperative microscopic findings as well as electrophysiologic monitoring and verification in 30 cases of large vestibular schwannomas. Preoperative DTI visualization of the facial nerve was successful in all cases and correlated well with the cisternal segment location of facial nerve during intraoperative observation in the 96.7% cases with good reproducibility and reliability; additionally, DTI showed moderate ability to distinguish morphologic changes between thin and compact varieties of facial nerves. Zhang et al. also determined the appropriate setting for facial nerve DTI fiber tracking.
T
Apart from location, morphologic alteration of facial nerves plays an important role intraoperatively, and prior knowledge of such change is definitely likely to further increase the chance of anatomic as well as functional preservation of facial nerves. Zhang et al.1 attempted to correlate the morphology of facial nerves by categorically dividing facial nerves into compact and flat varieties. In 2015, Yoshino et al.2 advocated combined use of diffusion tensor tractography and multifused contrast-enhanced fast imaging employing steady-state acquisition for prediction of the positions of facial and cochlear nerves in relation to vestibular schwannoma. Gerganov et al.3 classified the morphologic changes of facial nerves caused by large vestibular schwannomas into 2 varieties: compact and flat like an umbrella or lying splayed on the
1002
www.SCIENCEDIRECT.com
surface of the schwannoma. These authors further noted that DTI study findings failed to predict morphologic changes of facial nerves as a result of pressure effects of large vestibular schwannomas.3 Song et al.4 categorized facial nerve morphologic changes into 3 different categories: 1) wrapped in the arachnoid membrane, 2) parallel, or 3) adherent. They found no association between shape of the reconstructed DTI fiber bundles and the intraoperatively observed actual shape of the facial nerve. The study by Zhang et al.1 has a few concerns. First is the limited potential of DTI fiber tracking to distinguish the facial nerve from the vestibulocochlear nerve complex. Second, Zhang et al. categorized morphologic alterations of facial nerve into simple compact and flat types, but in reality different variations are reported based on assessment of the intraoperative phase. Finally, manual tracking results are highly dependent on the user and can be a biased factor affecting accuracy and utility of these imaging findings. Despite these concerns, Zhang et al. provide an important observation that can be used in the future for navigation guidance of facial nerve during microsurgical excision of large vestibular schwannomas. This will definitely further improve the feasibility of anatomic and functional preservation of the facial nerve and likely improve the confidence of neurosurgical team. Guru Dutta Satyarthee Department of Neurosurgery, Neurosciences Center, AIIMS New Delhi, New Delhi, India To whom correspondence should be addressed: Guru Dutta Satyarthee, M.Ch. [E-mail: [email protected]] http://dx.doi.org/10.1016/j.wneu.2017.04.039.
REFERENCES 1. Zhang Y, Mao Z, Wei P, Jin Y, Ma L, Zhang J, et al. Preoperative prediction of location and shape of facial nerve in patients with large vestibular schwannomas using diffusion tensor imaging-based fiber tracking. World Neurosurg. 2017;99: 70-78. 2. Yoshino M, Kin T, Ito A, Saito T, Nakagawa D, Ino K, et al. Combined use of diffusion tensor tractography and multifused contrast-enhanced FIESTA for predicting facial and cochlear nerve positions in relation to vestibular schwannoma. J Neurosurg. 2015;123:1480-1488. 3. Gerganov VM, Giordano M, Samii M, Samii A. Diffusion tensor imaging-based fiber tracking for prediction of the position of the facial nerve in relation to large vestibular schwannomas. J Neurosurg. 2011;115:1087-1093. 4. Song F, Hou Y, Sun G, Chen X, Xu B, Huang JH, et al. In vivo visualization of the facial nerve in patients with acoustic neuroma using diffusion tensor imagingbased fiber tracking. J Neurosurg. 2011;115:1087-1093.
105: 1002, SEPTEMBER 2017 WORLD NEUROSURGERY
