Derivative indices of optic nerve sheath diameter: a novel ultrasound-based approach for non-invasive intracranial pressure monitoring in neurocritical patients

Background Preoperative intracranial pressure (ICP) evaluation in neurocritical patients relies on computed tomography (CT) findings, which often lack accuracy. Ultrasound-measured optic nerve sheath diameter (ONSD) offers a non-invasive alternative, but optimal measurement protocols and indices remain controversial. Methods We conducted a retrospective cohort study of 45 neurocritical patients undergoing emergency craniotomy with invasive ICP monitoring between January 2023 and December 2025. Preoperative ultrasound measured ONSDint, ONSDext, and 8 derivative indices. Pearson correlation analysis, receiver operating characteristic (ROC) curves, and Kappa consistency tests were used to validate associations with invasive ICP measurements. Results All ONSD-derived indices correlated significantly with invasive ICP ( p < 0.01). Two indices exhibited superior diagnostic performance for identifying ICP ≥ 30 mmHg: ONSDint/OND (AUC = 0.980, sensitivity = 92.6%, specificity = 94.4%, optimal cutoff = 1.56) and ONSDint-OND (AUC = 0.980, sensitivity = 96.3%, specificity = 94.4%, optimal cutoff = 2.0). Kappa analysis showed almost perfect agreement between both indices and invasive monitoring (ONSDint/OND: Kappa = 0.775, accuracy = 88.9%; ONSDint-OND: Kappa = 0.86, accuracy = 93.3%). Conclusion ONSDint/OND and ONSDint-OND are reliable non-invasive biomarkers for predicting elevated ICP in neurocritical patients, providing valuable information to guide preoperative surgical decision-making. This study validates the clinical utility of ultrasound-derived ONSD indices in optimizing ICP assessment before craniotomy.