No Predictive Value of Aqueduct CSF Flow Dynamics for Shunt Response in Idiopathic Normal Pressure Hydrocephalus

INTRODUCTION: INPH is diagnosed based on clinical criteria and physiological measurements, including brain imaging parameters. Increased aqueductal CSF flow dynamics, assessed with Phase-Contrast MRI (PC-MRI), is one of the supportive features in iNPH diagnostic guidelines. A predictive value has been suggested but remains largely debatable. This study aimed to clarify the role of aqueductal flow in supporting diagnosis and shunt selection for iNPH patients. METHODS We retrospectively included 92 iNPH patients with preoperative PC-MRI together with pre- and post-operative gait speed measurement. Aqueductal CSF flow dynamics were calculated and correlated with gait outcomes and baseline gait speed. Additionally, we compared our cohort with 42 age-matched healthy controls. RESULTS We found no significant differences in CSF flow parameters between shunt responders and non-responders: Stroke volume was 130 ± 90 and 150 ± 100 µl, p = 0.32 respectively, with net flows of 0.06 ± 1.71 and − 0.07 ± 1.51 ml/min, p = 0.563. There were no correlations of aqueduct CSF dynamics with baseline gait performance, nor with gait change (-0.15 < R < 0.1, p > 0.5 for all parameters). Furthermore, comparisons with healthy controls revealed differences in stroke volume (140 ± 100µl iNPH vs 80 ± 41 healthy, p < 0.001) but not in net flow (p > 0.05). CONCLUSIONS Our findings indicate no significant predictive value of aqueductal CSF dynamics for shunt efficacy in iNPH patients. The heterogeneity of iNPH and variability in CSF dynamics across its time course, may contribute to these negative results. From a clinical point of view, aqueductal flow measured by 2D PC-MRI appears to have very limited value for selecting patients for shunting.