Facial Nerve Tractography of Vestibular Schwannomas: A Systematic Review of MR Acquisition and Analysis Pipelines.

[BACKGROUND] Facial nerve (CN VII) diffusion MR tractography is considered as a useful adjunct in pre-operative planning prior to vestibular schwannoma (VS) resection, especially in larger (Koos Grade III/IV) tumors. Since 2016, several systematic reviews have investigated the clinical value of CN VII tractography in VS, and all reported a "success rate" of at least 87% for predicting the pre-operative CN VII position. Yet in clinical practice, CN VII tractography has not yet been widely adopted into routine clinical practice. We suspected that underlying methodology and reporting metrics for existing tractography algorithms may be overestimating success rate. This motivated us to revisit the literature from a different perspective to unravel the caveats and nuances behind this technology.

[METHODS] We screened all published works on PubMed related to pre-operative CN VII tractography in VS. Twenty-two studies were reviewed in detail.

[RESULTS] We observed a strikingly high heterogeneity in tractography protocols in all domains of the tractography acquisition and analysis pipeline across studies.

[CONCLUSIONS] These findings suggest that the reliability and reproducibility of CN VII tractography in large VS has been overestimated. We believe that employing standardized reporting metrics, including sensitivity, true predictive value, and false discovery rate, would increase the transparency of benchmarking over other commonly reported metrics ("success rate" or "concordance rate"). In addition, ongoing research should aim to systematically investigate and improve each step in the acquisition and analysis pipeline for CN VII tractography in VS.