Post-Shunt Gait Improvement Correlates With Increased Cerebrospinal Fluid Peak Velocity In Normal Pressure Hydrocephalus: A Retrospective Observational Phase-Contrast Magnetic Resonance Imaging Study

Background: The relationship between peak velocity (PV) of cerebrospinal fluid (CSF) through the cerebral aqueduct and gait performance is not well characterized in normal pressure hydrocephalus (NPH) patients who undergo ventriculoperitoneal shunting (VPS). Therefore, our goal was to examine this relationship and test the hypothesis that aqueductal CSF PV in an NPH group is correlated with gait function pre-to post-shunt.Methods: Seven patients with idiopathic NPH who demonstrated gait improvement following large volume spinal tap or lumbar drain procedure and subsequent VPS were retrospectively studied. Patients underwent magnetic resonance imaging (MRI) and gait evaluation (functional ambulation performance [FAP] and gait time [ GT] tests) before and after VPS. Aqueductal crosssectional area (ACSA), PV, and total ventricular volume were obtained from semi-automatic segmentation of phase-contrast and 3D, T1-weighted MRIs while FAP and GT were obtained from neurological assessment. All mean changes pre-to post-VPS were tested using paired-sample t-tests, and all correlations using Pearson's correlation coefficient.Results: Mean PV increased 25% pre-to post-VPS (mean +/- standard deviation: 6.9 +/- 3.6 to 8.3 +/- 3.8 cm/s, P < 0.01); ACSA decreased 24% (6.5 +/- 2.6 to 4.8 +/- 1.9 mm(2), P < 0.05), FAP increased 14% (73.3 +/- 15.9 to 82.1 +/- 13.3, P = 0.05); total ventricular volume decreased 11% (140 +/- 27 to 124 +/- 25 cm(3), P < 0.01). GT decreased 14% (44.5 +/- 70.8 to 27.3 +/- 30.6 ms, P = 0.3), but the change was not statistically significant. Mean PV increase strongly correlated with ACSA decrease (R = 0.90, P < 0.01), FAP increase (R = 0.76, P < 0.05), and GT decrease (R = 0.91, P < 0.01).Conclusions: The observed relationships between PV and gait metrics, and PV and ACSA independently suggest a complex and dynamic biophysical mechanism common to NPH patients undergoing shunt placement. A larger prospective study with longitudinal measures is warranted.