Position-related variability of CSF opening pressure measurements

BACKGROUND AND PURPOSE: Normative data for CSF OP have previously been established with patients in the LD position. During fluoroscopically guided LP procedures, radiologists frequently obtain these OP measurements with patients prone. In this prospective study, our goal was to determine the variability of OP measurements as a function of patient positioning and to assess whether there is a relationship with patient BMI. MATERIALS AND METHODS: Consecutive patients reporting for fluoroscopically guided LP or myelography were enrolled. OP was measured with the patient in 3 positions, with the order of the technique randomized: prone with table flat, prone with table tilted until the hub of the needle was at the level of the right atrium, and LD with the needle hub at the level of the spinal canal. The BMI of each patient was calculated. The Wilcoxon signed-rank test and linear regression analysis with bivariate fit of difference were used for analysis. RESULTS: OP measurements with the patient in the prone position were significantly elevated compared with those in the LD position, with mean differences of 2.7 (P < .001) and 1.6 cm H₂O, (P = .017) for prone flat and prone tilted, respectively. There was no significant difference in OP measurements for the prone flat versus prone tilted positions (P = .20). There was no correlation between BMI and observed differences (LD-flat: R² = 0.00028; LD-tilt: R² = 0.00038; prone-tilt: R² = 0.00000020). CONCLUSIONS: Measuring OP with the patient in the prone position may result in overestimation of CSF pressure. Table tilt did not significantly impact mean prone OP. Radiologists should specify exact patient positioning when reporting OP measurements.