This study aims to investigate the interrelationship between body mass index (BMI), venous sinus pressure (VSP), and craniospinal elastance in determining lumbar puncture opening pressure (LP OP).

Previous studies have established independent correlations between BMI, VSP, and craniospinal elastance with LP OP in idiopathic intracranial hypertension (IIH), but their mechanistic interactions remain poorly understood.

A single-center retrospective chart review was conducted to identify patients who received venous manometry (8/2021-11/2025) followed by LP within 7 days before stenting. VSPs were measured at standardized locations, including the torcula (TP) and sigmoid/jugular (SIJ) sinuses. Elastance was calculated as (OP – closing pressure)/volume of CSF removed. Statistical analysis (JASP 0.19.3) was performed using Pearson correlation and generalized linear model (Gaussian identity; scaled center) to assess relationships between LP OP, BMI, TP, elastance, and BMI*elastance while controlling for age and sex.

135 patients were screened, and 28 patients (all refractory IIH; 92.9% female, BMI 38.2±9.5) were included for review. Among them, 14 (50.0%) were Caucasian, 11 (39.3%) were African American, and 3 (10.7%) were of other ethnicities. Mean LP OP 32.7±14.1cmH₂O, mean TP 30.0±15.8mmHg, mean average SIJ 15.6±6.5mmHg, and mean craniospinal elastance 0.784±0.377cmH₂O/ml. BMI was significantly correlated with LP OP but not with elastance. TP, elastance, and BMI*elastance interaction were significant factors associated with LP OP. BMI's effect on LP OP became significantly stronger as elastance increased.

Our results demonstrate that elastance plays a role in modulating the influence of BMI on LP OP. Patients with elevated elastance may be particularly vulnerable to BMI-related pressure increases. Future larger studies are needed to verify our findings and better understand the pathophysiology behind elevated intracranial pressure in IIH.