OBJECTIVE:Hearing preservation in vestibular schwannoma (VS) surgery remains challenging due to frequent cochlear nerve displacement and the limited reliability of brainstem auditory evoked potentials (BAEPs) once waveforms deteriorate. This study evaluated the feasibility and clinical utility of bipolar handheld cochlear nerve action potential (CNAP) mapping for intraoperative nerve identification and compared its prognostic performance with BAEP monitoring. METHODS:In this retrospective single-center cohort, 193 patients with histologically confirmed VS underwent intraoperative auditory mapping between September 2021 and November 2024. Two color-coded bipolar handheld probes were used: one for facial nerve stimulation and the other for near-field CNAP recording along the presumed cochlear nerve course. CNAP responses were considered favorable if waveforms remained stable or decreased by < 50% in amplitude. Functional hearing preservation (American Academy of Otolaryngology-Head and Neck Surgery class A-C) served as the primary endpoint. Logistic regression and receiver operating characteristic (ROC) analyses evaluated predictive performance. RESULTS:CNAP mapping identified the cochlear nerve in 83.4% of cases, significantly higher than intraoperative BAEP elicitation (46.1%; p < 0.001). Favorable CNAP responses were strongly associated with hearing preservation (91.4% vs 8.1%, p < 0.001; adjusted OR 37.0, 95% CI 9.28-217.8). The combined CNAP + BAEP model showed excellent discrimination (area under the ROC curve = 0.91) and good calibration (p = 0.24, Hosmer-Lemeshow test). CONCLUSIONS:CNAP mapping enabled real-time functional localization of the cochlear nerve and provided complementary intraoperative functional information. While postoperative hearing remains dependent on the structural integrity of the cochlear nerve, particularly in large tumors, CNAP mapping provides complementary functional information strongly associated with hearing preservation.
M. Gazi Yaşargil, often called the "father of modern microneurosurgery," fundamentally reshaped neurosurgery through a philosophy emphasizing precision and functional preservation. Despite his widely acknowledged legacy, no comprehensive, data-driven analysis has consolidated the full scope of his clinical and scholarly impact. This study combines a narrative synthesis of Yaşargil's work with a bibliometric meta-analysis of his publications from 1952 to 2024, evaluating contributions across anatomical approaches, technical innovations, therapeutic strategies, surgical outcomes, and academic influence. Findings highlight foundational anatomical approaches, such as the pterional craniotomy, and key technical innovations, including specialized microsurgical instruments. His therapeutic strategies achieved durable outcomes, with > 90% obliteration rates in selected vascular cohorts and Engel class I seizure freedom in approximately 70% of epilepsy cases. Bibliometric analysis of 145 publications (approximately 15,089 citations) shows his sustained scholarly influence, with 2748 citations accrued since 2020, particularly in epilepsy and tumor research. This work underscores Yaşargil's enduring impact: anatomy-driven, transferable strategies that remain central to contemporary neurosurgical practice, even amid advances in robotics, endovascular techniques, and image guidance.
OBJECTIVE:Postoperative visual field deficits (VFDs) following anterior temporal epilepsy surgery often result from Meyer's loop (ML) injury. Optic radiation (OR) tractography aids surgical planning, but accuracy varies by method. Deterministic diffusion tensor imaging (Det-DTI) tractography underrepresents fiber complexity, whereas constrained spherical deconvolution with probabilistic tracking (Prob-CSD) resolves crossing fibers and improves anatomical fidelity. The aim of this study was to compare Det-DTI and Prob-CSD for OR/ML delineation and to evaluate accuracy by correlating tract injury with postoperative VFD severity. METHODS:Adults who underwent anterior temporal epilepsy surgery at two centers (Alfred Hospital in Melbourne, Australia; Vanderbilt University Medical Center in Nashville, Tennessee, US) were included. All patients underwent pre- and postoperative T1-weighted and diffusion-weighted MRI and automated postoperative perimetry. Det-DTI and Prob-CSD tractography pipelines, using the same expert-guided regions of interest, were compared. Tract injury was quantified as volumetric overlap between reconstructed ORs and resection cavities. VFD severity was measured as quadrant-specific visual field (QsVF) scores from perimetry. Reconstructed tract and estimated injury volumes were compared using the Wilcoxon signed-rank test, and their correlations with QsVF were assessed using Pearson correlation. Linear regression was used to assess whether Prob-CSD-estimated tract injury independently predicted postoperative QsVF, with resection volume and surgical technique as covariates. RESULTS:Overall, 33 patients (19 female, median age 39.1 years; 30 right handed and 11 left sided) were included in the analysis. Surgery comprised 9 anterior temporal lobectomies, 21 selective amygdalohippocampectomies, and 3 lesionectomies. Compared with Det-DTI, Prob-CSD tractography delineated significantly larger OR volumes (mean 20.18 ± 4.76 cm3 vs 1.48 ± 1.05 cm3; p = 8.34 ×10-7) and identified greater tract injury volumes (mean 0.60 ± 0.81 cm3 vs 0.04 ± 0.16 cm3; p = 3.7 ×10-6). Det-DTI failed to reconstruct ML in all but one case. Prob-CSD tract injury volumes correlated strongly with postoperative QsVF scores (r = -0.63, p = 7.35 ×10-5), whereas Det-DTI showed a weaker nonsignificant association (r = -0.31, p = 0.08). Linear regression confirmed independent association between Prob-CSD tract injury and postoperative VFD severity (p = 0.002, SE = 7.23 ×10-5, adjusted R2 = 0.34). CONCLUSIONS:Prob-CSD tractography outperformed Det-DTI in reconstructing ML and reliably predicting postoperative VFDs, regardless of surgical technique and resection extent. Det-DTI should be avoided for ML tractography. This study strongly supports incorporating expert-guided Prob-CSD into preoperative planning to enhance patient counseling and reduce risk of visual morbidity following temporal resection.
