Identification of the Facial Nerve in Relation to Vestibular Schwannoma Using Preoperative Diffusion Tensor Tractography and Intraoperative Tractography-Integrated Neuronavigation System

doi:10.1016/j.wneu.2017.08.048

World Neurosurgery

Volume 107, November 2017, Pages 669-677

https://doi.org/10.1016/j.wneu.2017.08.048 Get rights and content

Background

Preoperative visualization of the facial nerve could help neurosurgeons to prevent facial nerve injury during vestibular schwannoma surgery. Some studies have addressed diffusion tensor tractography (DTT) for preoperative identification of the facial nerve. However, few studies have focused on tractography-integrated neuronavigation for DTT verification. This study aimed to explore the appropriate DTT tracing parameters and evaluate the effect of intraoperative facial nerve tractography-integrated neuronavigation for verifying the DTT accuracy.

Methods

Patients who underwent vestibular schwannoma surgery between September 2013 and August 2015 were included. Clinical features were recorded. All patients underwent preoperative DTT with 2 seed regions of interest and a variable fractional anisotropy threshold. Intraoperatively, the facial fiber tract guided by the neuronavigation was compared with the real location of facial nerve so that the accuracy of DTT was verified. Postoperative facial nerve function of each patients was followed up.

Results

Nineteen patients were enrolled in this study. Successful facial fiber tracts was obtained in 18 patients. In 17 of the 18 patients, intraoperative navigation confirmed DTT accuracy. The facial nerves were located on the anterior middle third of the tumor in 9 patients. Twelve months after surgery, facial nerve function was classified as grade I in 10 patients and grade II in 8 patients.

Conclusions

We consider preoperative DTT with intraoperative tractography-integrated neuronavigation to be a useful method for identifying the location of the facial nerve. This method might improve facial nerve preservation.

Introduction

The focus of vestibular schwannoma (VS) surgery is maximum resection of the tumor and maximum preservation of cranial nerve function.1, 2, 3 With the development of microsurgery, postoperative normal or near-normal facial nerve function has been reported to be up to 90%.3, 4, 5, 6 However, the preservation of the facial nerve when removing large or tough VS remains a challenge, even in experienced hands. The difficulty lies in the great variation in the location and the morphologic changes of the facial nerve.⁷ Facial nerve paresis can be a devastating complication, leading to a lower quality of life. Preoperative visualization of the facial nerve location is a long-desired wish of neurosurgeons. The application of diffusion tensor tractography (DTT) in VS surgery has turned it into reality. In recent years, many investigators have reported their experience with preoperative identification of the facial nerve in VS surgery using DTT. However, their methods and results have varied.8, 9, 10, 11, 12, 13, 14 In addition, no uniform standard of verifying the accuracy of DTT has been achieved. Few investigators have mentioned the application of a tractography-integrated neuronavigation system for real-time verification of tractography accuracy. The aim of this study was to determine the appropriate region of interest (ROI) and fractional anisotropy (FA) threshold that influence the successful rates of facial nerve tracing and to evaluate the effect of intraoperative tractography-integrated neuronavigation for verifying DTT accuracy in VS surgery.

Section snippets

Patient Population and Neuroradiologic Evaluation

Patients admitted to the Department of Neurosurgery at Beijing Tiantan Hospital between September 2013 and August 2015 who were diagnosed with VS and agreed to undergo DTT procedure and tumor resection were included in this clinical study. Patients who had previously received stereotactic radiotherapy or VS surgery were excluded from this study. Those who could not cooperate or made obvious head movements in the procedure of diffusion tensor imaging (DTI) scanning were also excluded. All

Clinical Features

A total of 23 consecutive patients were included in this study. Among them, 3 had a previous history of stereotactic radiotherapy or VS surgery and 1 patient failed to receive the DTI scanning. They were excluded from the study. Therefore, 19 patients were enrolled in this study and the clinical records were analyzed. The mean age of the patients was 31.4 years (range, 19–62 years). The male/female ratio was 8:11. The mean diameter of the VSs was 41.3 mm (range, 25.0–53.4 mm). The Hannover

Discussion

The main goal of VS surgery is to totally remove the tumor with maximum preservation of facial nerve function.1, 2, 3, 5, 6 However, it is difficult to achieve the functional preservation of the facial nerve when a large tumor is encountered. The facial nerve is always displaced and morphologically changed in an unpredictable manner,⁷ making the intraoperative identification of the facial nerve difficult, even by a skilled neurosurgeon.3, 19 Facial nerve injury leads to a decreased quality of

Conclusions

DTT provides a new method to preoperatively visualize the facial nerve for VS surgery. Adopting a 2-ROI strategy and variable FA threshold specific to the patient might increase the success rate of the tractography. The tractography-integrated neuronavigation system provides a live verification of DTT accuracy. However, navigation drift might influence the accuracy and lead to an incorrect identification. Therefore, the neurosurgeon should make a comprehensive judgment based on their own visual

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We aim to evaluate the usefulness of preoperative facial nerve tractography in determining the facial nerve position in cerebellopontine angle tumor resection and its value in helping to preserve facial nerve function during surgery.
A prospective study was designed to include patients presenting with cerebellopontine angle tumors. Three-dimensional reconstruction of facial nerve tractography was performed and added to the usual preoperative testing in all patients. Facial nerve position was compared between tractography results and surgical findings. Moreover, facial nerve function was evaluated at baseline and during follow-up.
Fifteen patients were included for analysis. Complete resection was obtained in 5 patients, near-total resection was achieved in 8 patients, and partial resection in 2 patients. We found a strong statistically significant concordance between the preoperative facial nerve tractography reconstruction and the intraoperative findings (complete concordance in 86.66% of all the cases; κ = 0.784; P < 0.0001). Facial nerve anatomic structure was preserved in all patients during surgery. At 6 months follow-up, 66.66% of patients had a facial nerve normal function or a mild dysfunction.
Preoperative facial nerve tractography reconstruction showed a high correlation with intraoperative findings. Preoperative tractography information regarding facial nerve position and its cisternal course is valuable information and could help the surgeon in increasing the safety of the procedure during cerebellopontine angle tumor surgery.
ACR Appropriateness Criteria® Cranial Neuropathy: 2022 Update
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Citation Excerpt :
DTI is an advanced imaging technique that may be useful in assessing the facial nerve. Several studies suggest that DTI is accurate for the preoperative localization of the cisternal facial nerve to avoid iatrogenic injury in patients with cerebellopontine angle tumors [107,126-128]. Research indicates that DTI may have future use localizing the intraparotid facial nerve and detecting perineural spread of tumor [129,130].
Cranial neuropathy can result from pathology affecting the nerve fibers at any point and requires imaging of the entire course of the nerve from its nucleus to the end organ in order to identify a cause. MRI with and without intravenous contrast is often the modality of choice with CT playing a complementary role. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer-reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer-reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.
Reliability of Preoperative Prediction of the Location of the Facial Nerve Using Diffusion Tensor Imaging–Fiber Tracking in Vestibular Schwannoma: A Systematic Review and Meta-Analysis
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According to the results of intraoperative validation, facial nerves were verified but discordant in 21 patients. The main reasons included a thinned and compressed facial nerve19,20,24,26 and a cystic component of the VS.5,6,21,23,28 Separation of the wall of the cystic VSs and the thinned and compressed facial nerve is a giant challenge during surgery.29 Compared with solid VS, most studies have reported that cystic VS are tumors with characteristics of rapid growth, large size, short clinical history of symptoms, and sudden deterioration because of unpredictable expansion of the cystic component or hemorrhage.
The popularization and application of microscopy, the in-depth study of the microanatomy of the cerebellopontine angle, and the application of intraoperative electrophysiological monitoring technology to preserve facial nerve function have laid a solid foundation for the modern era of neurosurgery. The preoperative prediction of the location of the facial nerve is a long-desired goal of neurosurgeons. The advances in neuroimaging seem to be making this goal a reality. Many studies investigating the reliability of the preoperative prediction of the location of the facial nerve using diffusion tensor imaging-fiber tracking in vestibular schwannoma have been reported in the last 20 years. The PubMed, Embase, and Cochrane databases were searched for articles published before March 30, 2020. A comprehensive review of published studies was carried out in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Authors performed a systematic review and meta-analysis of the reported data to assess the reliability of the preoperative prediction of the location of the facial nerve using diffusion tensor imaging-fiber tracking in vestibular schwannoma. The data were analyzed using a fixed-effects model. The estimated overall intraoperative verification concordance rate was 89.05% (95% confidence interval 85.06%–92.58%). Preoperatively predicting the location of the facial nerve using diffusion tensor imaging-fiber tracking in vestibular schwannoma is reliable, but the extent to which it contributes to long-term facial nerve function is still unclear. To further verify these results, studies with larger sample sizes are needed in the future, especially prospective randomized controlled trials focusing on the long-term functional preservation of the facial nerve.
Integrating tractography in pelvic surgery: a proof of concept
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To show the interest of tractography in pelvic surgery by a demonstrative case of neurofibroma resected by robotic assisted laparoscopy.
Although diffusion tensor magnetic resonance imaging, along with tractography algorithms, is increasingly included in image guided neurosurgery methods, it is less frequently used for the peripheral nervous system such as the pelvic sacral plexus. We report one observation demonstrating the interest of such image data for pelvic surgery.
A 12-years-old girl with neurofibromatosis presented with a growing left pelvic neurofibroma on repeated pelvic MRI with an increased SUV (2.83) on PET scan. A diffusion tensor pelvic MRI was performed before and after robotically assisted tumoral resection, and a tractography algorithm was applied on both images.
The pre-operative tractogram showed the nervous nature of the tumor in close contact with the left sacral plexus. Section of a nerve trunk encased in the neurofibroma was mandatory for the resection and well documented by the 3D enhanced vision provided by the robot. Post-operatively, the patient showed a slight paresthesia and dysesthesia of the left leg calf and of the plantar vault (left S2 territory), without any motor deficit. The post-operative tractogram showed a thinning of the left S2 sacral root and the disappearance of right aberrant nervous tracts.
This clinical case validates the ability of pelvic tractography to deliver a proper imaging of the sacral nervous network and emphasizes the potential usefulness of this approach in pelvic surgery management, with perspectives of image-guided surgery.
Preoperative Prediction of Facial Nerve in Patients with Vestibular Schwannomas: The Role of Diffusion Tensor Imaging—A Systematic Review
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In addition, IONM for FN has had the same limitations.9 Thus, FN tractography, which is the only method capable of mapping white matter fibers at present, seems to be a valid tool for predicting the exact course of the FN and its spatial relationships to the VS.12-24 The VSs analyzed in the included studies were predominantly large (98.7%).
In vestibular schwannoma surgery, the preservation of facial and cochlear nerves is of paramount concern regarding to their effect on patients' quality of life. The rate of nerve function preservation has increased with advancements in surgical technique and neuroimaging and the introduction of intraoperative neuromonitoring. The preoperative depiction of anatomical issues between the nerves and tumor could help in surgical planning. Many studies investigating advanced imaging for cranial nerves detection, in particular diffusion tensor imaging, have been reported in the past decade. A systematic review of the reported data evaluating preoperative facial nerve fiber tracking, followed by intraoperative verification, was conducted. Seventeen studies with 223 patients (mean age, 47.5 years; range 17–77; male/female ratio 1:1.4) met our inclusion criteria. Preoperative facial nerve fiber tracking was obtained for 214 patients (96%), and subsequent intraoperative verification revealed a correct prediction for 187 cases (85.5%). The results from the present review have confirmed that preoperative fiber tracking for facial nerve identification during large vestibular schwannoma surgery is valuable and reliable. However, the included studies were not comparable in terms of images, acquisitions, or postprocessing elaboration. Larger series and homogenous magnetic resonance imaging parameters are required to strengthen these findings.
Application of diffusion tensor imaging of the facial nerve in preoperative planning for large vestibular schwannoma: a systematic review
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: Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

: Huan Li and Liang Wang are co-first authors.

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Original ArticleIdentification of the Facial Nerve in Relation to Vestibular Schwannoma Using Preoperative Diffusion Tensor Tractography and Intraoperative Tractography-Integrated Neuronavigation System

Background

Methods

Results

Conclusions

Introduction

Section snippets

Patient Population and Neuroradiologic Evaluation

Clinical Features

Discussion

Conclusions

Eur J Radiol

Management of 1000 vestibular schwannomas (acoustic neuromas): clinical presentation

Neurosurgery

Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them

Neurosurgery

Management of 1000 vestibular schwannomas (acoustic neuromas): the facial nerve-preservation and restitution of function

Neurosurgery

Prognostic significance of peritumoral edema in patients with vestibular schwannomas

Neurosurgery

Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients

J Neurosurg

Improved preservation of function during acoustic neuroma surgery

J Neurosurg

Microanatomical variations in the cerebellopontine angle associated with vestibular schwannomas (acoustic neuromas): a retrospective study of 1006 consecutive cases

J Neurosurg

Feasibility of diffusion tensor tractography for preoperative prediction of the location of the facial and vestibulocochlear nerves in relation to vestibular schwannoma

Acta Neurochir (Wien)

Facial nerve preservation with preoperative identification and intraoperative monitoring in large vestibular schwannoma surgery

Acta Neurochir (Wien)

Preoperative identification of the facial nerve in patients with large cerebellopontine angle tumors using high-density diffusion tensor imaging

J Neurosurg

Diffusion tensor imaging-based fiber tracking for prediction of the position of the facial nerve in relation to large vestibular schwannomas

J Neurosurg

Displacement of the facial nerve course by vestibular schwannoma: preoperative visualization using diffusion tensor tractography

J Magn Reson Imaging

Identification of cranial nerves near large vestibular schwannomas using superselective diffusion tensor tractography: experience with 23 cases

Acta Neurochir (Wien)

Preoperative identification of facial nerve in vestibular schwannomas surgery using diffusion tensor tractography

J Korean Neurosurg Soc

Microsurgical anatomy around the foramen of Luschka in relation to intraoperative recording of auditory evoked potentials from the cochlear nuclei

J Neurosurg

Original Article
Identification of the Facial Nerve in Relation to Vestibular Schwannoma Using Preoperative Diffusion Tensor Tractography and Intraoperative Tractography-Integrated Neuronavigation System