Super-resolution Diffusion Tensor Imaging for Delineating the Facial Nerve in Patients with Vestibular Schwannoma

Preoperative Vascular and Cranial Nerve Imaging in Skull Base Tumors

Skull base tumors such as meningiomas and schwannomas are often pathologically benign. However, surgery for these tumors poses significant challenges because of their proximity to critical structures such as the brainstem, cerebral arteries, veins, and cranial nerves. These structures are compressed or encased by the tumor as they grow, increasing the risk of unintended injury to these structures, which can potentially lead to severe neurological deficits. Preoperative imaging is crucial for assessing the tumor size, location, and its relationship with adjacent vital structures. This study reviews advanced imaging techniques that allow detailed visualization of vascular structures and cranial nerves. Contrast-enhanced computed tomography and digital subtraction angiography are optimal for evaluating vascular structures, whereas magnetic resonance imaging (MRI) with high-resolution T2-weighted images and diffusion tensor imaging are optimal for evaluating cranial nerves. These methods help surgeons plan tumor resection strategies, including surgical approaches, more precisely. An accurate preoperative assessment can contribute to safe tumor resection and preserve neurological function. Additionally, we report the MRI contrast defect sign in skull base meningiomas, which suggests cranial nerve penetration through the tumor. This is an essential finding for inferring the course of cranial nerves completely encased within the tumor. These preoperative imaging techniques have the potential to improve the outcomes of patients with skull base tumors. Furthermore, this study highlights the importance of multimodal imaging approaches and discusses future directions for imaging technology that could further develop preoperative surgical simulations and improve the quality of complex skull base tumor surgeries.

To explore the pathogenesis of Bell's palsy using diffusion tensor image

To explore the pathogenesis of Bell's palsy using the diffusion tensor image on 3.0 T MR. The healthy people and the patients with Bell's palsy underwent intraparotid facial nerve scanning by using the DTI and T1 structural sequence at 3.0 T MR. The raw DTI data were performed affine transformation and nonlinear registration in the common MNI152_T1 space and resampled to the 0.4 mm3 voxel size. A group of 4 spherical seed regions were placed on the intratemporal facial nerves in the common space, bilaterally and symmetrically. The DTI data in the common space were used to track the intratemporal facial nerve fibers by using TrackVis and its Diffusion Toolkit. Each tractography was used to construct the maximum probability map (MPM) according to the majority rule. The fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) were calculated and extracted on the basis of MPM. For healthy people, there was no significant difference in FA, MD, RD and AD of bilateral facial nerves. For patients with Bell's palsy, there was no significant difference in AD, there was significant difference in FA, MD and RD between the affected nerve and the healthy nerve (P < 0.02). This study showed that the myelin sheath injury of the intratemporal facial nerve is the main cause of Bell's palsy. Most neural axons are not damaged. The results may explain the pathogenesis of the Bell's palsy, which is self-limited for most cases.

New and Advanced Magnetic Resonance Imaging Diagnostic Imaging Techniques in the Evaluation of Cranial Nerves and the Skull Base

The skull base and cranial nerves are technically challenging to evaluate using magnetic resonance (MR) imaging, owing to a combination of anatomic complexity and artifacts. However, improvements in hardware, software and sequence development seek to address these challenges. This section will discuss cranial nerve imaging, with particular attention to the techniques, applications and limitations of MR neurography, diffusion tensor imaging and tractography. Advanced MR imaging techniques for skull base pathology will also be discussed, including diffusion-weighted imaging, perfusion and permeability imaging, with a particular focus on practical applications.

Three-dimensional (3D) Printed Vestibular Schwannoma for Facial Nerve Tractography Validation

OBJECTIVES

Predicting the course of cranial nerve (CN) VII in the cerebellopontine angle (CPA) on preoperative imaging for vestibular schwannoma (VS) may help guide surgical resection and reduce complications. Diffusion MRI based tractography has been used to identify cranial nerve trajectory, but intraoperative validation of this novel approach is challenging. Currently, validation is based on operative report descriptions of the course of cranial nerves, but yields a simplified picture of the three-dimensional (3D) course of CN VII. In this study, we investigate the accuracy of tractography with detailed patient-specific 3D-printed VS tumors.

DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PARTICIPANTS

Twenty adult VS surgical candidates.

MAIN OUTCOME MEASURES

We compared tractography with intraoperative 3D course of CN VII. The surgeons were blinded to tractography and drew the intraoperative course of the CN VII on a patient specific 3D-printed tumor model for detailed comparison with tractography.

RESULTS

Of 20 patients, one was excluded due to subtotal removal and inability to assess CN VII course. In the remaining 19 patients, 84% (16/19) tractography was successful. In 94% of tumors with tractography (15/16), the intraoperative description of CN VII course matched the tractography finding. The maximum distance, however, between tractography and intraoperative course of CN VII was 3.7 mm ± 4.2 mm.

CONCLUSION

This study presents a novel approach to CN VII tractography validation in VS. Although descriptions of CN VII intraoperatively match tractography, caution is warranted as quantitative measures suggest a clinically significant distance between tractography and CN VII course.

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

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.