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BACKGROUND AND PURPOSE: Tractography of the facial nerve based on single-shell diffusion MR imaging is thought to be helpful before surgery for resection of vestibular schwannoma. However, this paradigm can be vitiated by the isotropic diffusion of the CSF, the convoluted path of the facial nerve, and its crossing with other bundles. Here we propose a multishell diffusion MR imaging acquisition scheme combined with probabilistic tractography that has the potential to provide a presurgical facial nerve reconstruction uncontaminated by such effects. MATERIALS AND METHODS: Five patients scheduled for vestibular schwannoma resection underwent multishell diffusion MR imaging (b-values = 0, 300, 1000, 2000 s/mm2). Facial nerve tractography was performed with a probabilistic algorithm and anatomic seeds located in the brain stem, cerebellopontine cistern, and internal auditory canal. A single-shell diffusion MR imaging (b-value = 0, 1000 s/mm2) subset was extrapolated from the multishell diffusion MR imaging data. The quality of the facial nerve reconstruction based on both multishell diffusion MR imaging and single-shell diffusion MR imaging sequences was assessed against intraoperative videos recorded during the operation. RESULTS: Single-shell diffusion MR imaging–based tractography was characterized by failures in facial nerve tracking (2/5 cases) and inaccurate facial nerve reconstructions displaying false-positives and partial volume effects. In contrast, multishell diffusion MR imaging–based tractography provided accurate facial nerve reconstructions (4/5 cases), even in the presence of ostensibly complex patterns. CONCLUSIONS: In comparison with single-shell diffusion MR imaging, the combination of multishell diffusion MR imaging–based tractography and probabilistic algorithms is a more valuable aid for surgeons before vestibular schwannoma resection, providing more accurate facial nerve reconstructions, which may ultimately improve the postsurgical patient’s outcome.

Gliomas are amongst the most common primary brain tumours in adults and are often associated with poor prognosis. Understanding the extent of white matter (WM) which is affected outside the tumoral lesion may be of paramount importance to explain cognitive deficits and the clinical progression of the disease. To this end, we explored both direct (i.e., tractography based) and indirect (i.e., atlas-based) approaches to quantifying WM structural disconnections in a cohort of 44 high- and low-grade glioma patients. While these methodologies have recently gained popularity in the context of stroke and other pathologies, to our knowledge, this is the first time they are applied in patients with brain tumours. More specifically, in this work, we present a quantitative comparison of the disconnection maps provided by the two methodologies by applying well-known metrics of spatial similarity, extension, and correlation. Given the important role the oedematous tissue plays in the physiopathology of tumours, we performed these analyses both by including and excluding it in the definition of the tumoral lesion. This was done to investigate possible differences determined by this choice. We found that direct and indirect approaches offer two distinct pictures of structural disconnections in patients affected by brain gliomas, presenting key differences in several regions of the brain. Following the outcomes of our analysis, we eventually discuss the strengths and pitfalls of these two approaches when applied in this critical field.

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.