The visuo-operative angle: computational 3D assessment of surgical trajectories toward irregular target areas in skull base corridors.

[OBJECTIVE] The aim of this study was to introduce the visuo-operative angle (VOA) as a novel neuroanatomical metric for quantifying surgical exposure and visibility in skull base microsurgery. The VOA measures the alignment between surgical trajectories and target exposure areas in 3D space. Additionally, the authors explored its implementation in 3D photogrammetry of cadaveric models and 3D-segmented presurgical imaging models to assess the feasibility of VOA in experimental and clinical settings.

[METHODS] Five latex-injected human cadaveric specimens were used to evaluate various endoscopic and microscopic approaches. The VOA was calculated as the angle formed by the surgical trajectory line and the plane of the target exposure area. Photogrammetry was used to generate high-resolution 3D models of the dissected regions and replicate the measurement virtually. Finally, a clinical exploratory trial was conducted in a patient undergoing an endoscopic endonasal approach for a pituitary neuroendocrine tumor (PitNET) with clival erosion. Three-dimensional-rendered preoperative imaging was used to define and measure the target clival region and its VOA, and intraoperative neuronavigation validated the measurement.

[RESULTS] VOA showed excellent interrater agreement across 36 target areas (bias ≤ 1°, within-subject coefficient of variation 1%-6%). Endoscopic and microscopic findings were consistent with prior literature using different exposure metrics and expert opinion while adding surgically relevant detail on trajectory visibility and instrument direction toward deep targets (e.g., an endoscopic transorbital approach [ETOA] vs a transmaxillary approach to Meckel's cave and the anterolateral triangle; subtemporal vs translabyrinthine/retrosigmoid approaches to the internal acoustic canal; frontotemporal-orbitozygomatic approach vs ETOA at the clinoid triangle). Photogrammetry yielded measurements highly concordant with cadaveric data. Presurgical estimates (VOA approximately 52.7°) aligned with intraoperative values (53.5°), supporting the feasibility of the VOA as an analytical tool for approach analysis and modeling.

[CONCLUSIONS] The VOA is a simple, reproducible geometrical metric (in degrees) that relates the surgeon's line of sight and instrument path to the target plane, adding directional detail not captured by conventional metrics. Integrated with photogrammetry and 3D-segmented imaging, the VOA enables the quantitative comparison of corridors and approach variants, as well as supporting regional anatomy modeling. Early results are promising, but larger cadaveric series and multicase clinical studies are needed to establish the accuracy, robustness, and applicability of this metric across anatomical research, surgical planning, and intraoperative calculations.