Abstract
<title>Abstract</title> <p>Background Diagnostic criteria for idiopathic intracranial hypertension (IIH) rely partly on lumbar puncture opening pressure, which may not capture the dynamic pressure-volume properties of the craniospinal system. Lumbar infusion testing (LIT) enables multidimensional assessment of cerebrospinal fluid dynamics during controlled volume loading. We characterized LIT-derived physiological variability in pediatric IIH and explored its association with longitudinal optical coherence tomography (OCT) outcomes. Methods This retrospective single-center study included 21 pediatric patients with IIH diagnosed according to the Friedman criteria between 2023 and 2026. LIT-derived measures of pressure response, apparent cerebrospinal fluid outflow resistance, pressure-volume reserve, pulsatility, and slow-wave activity were analyzed. Principal component analysis (PCA) was performed on 20 complete-case infusion studies. The first principal component was interpreted as a continuous pressure-volume reserve score and evaluated as an exploratory predictor of longitudinal global retinal nerve fiber layer thickness (RNFL G) and ganglion cell complex thickness (GCC). Results Mean age at diagnosis was 9.07 ± 4.52 years. Median baseline and plateau intracranial pressures were 19.69 mmHg [IQR 15.62–23.85] and 32.99 mmHg [26.12–35.41], respectively. The first two principal components explained 70.93% of total variance. PC1 accounted for 45.95% and contrasted greater compliance and pressure-amplitude coupling with higher plateau pressure, higher apparent outflow resistance, and a steeper infusion slope, defining a continuous pressure-volume reserve axis. OCT follow-up was available in 20/21 patients. In the pre-surgical RNFL model, PC1 and the time-by-PC1 interaction were significant, indicating steeper RNFL reduction over time toward the lower-reserve end of the axis. This interaction was not significant in the smaller postoperative subgroup, and GCC findings did not show a consistent longitudinal interaction. Conclusions Pediatric IIH demonstrated marked LIT-derived physiological heterogeneity organized predominantly along a continuous pressure-volume reserve axis rather than by baseline pressure alone. The association between this axis and pre-surgical RNFL trajectories suggests that multiparametric LIT may provide clinically relevant physiological information beyond opening pressure. Prospective studies with standardized LIT and OCT protocols are required to validate these findings.</p>