Intracranial volumetric changes govern cerebrospinal fluid flow in the Aqueduct of Sylvius in healthy adults

Purpose: To characterize the intracranial volumetric changes that influence the cerebrospinal fluid (CSF) pulse in the Aqueduct of Sylvius (AoS). Materials and Methods: Neck MRI data were acquired from 12 healthy adults (8 female and 4 males; mean age=30.9 years), using a 1.5 Tesla scanner. The intracranial arterial, venous and CSF volumes changes, together with the aqueductal CSF (aCSF) volume, were estimated from flow rate data acquired at C2/C3 level and in the AoS. The correlations and temporal relationships among these volumes were computed. Results: The aCSF volumetric changes were strongly correlated (r = 0.967, p<0.001) with the changes in intracranial venous volume, whose peak occurred 7.0% of cardiac cycle (p = 0.023) before peak aCSF volume, but less correlated with the intracranial arterial and CSF volume changes (r=-0.664 and 0.676 respectively, p<0.001). The intracranial CSF volume change was correlated with the intracranial venous volume change (r=0.820, p<0.001), whose peak occurred slightly before (4.2% of CC, p=0.059). Conclusion: The aCSF pulse is strongly correlated with intracranial venous volume, with expansion of the cortical veins occurring prior to aCSF flow towards the third ventricle. Both caudal-cranial aCSF flow and venous blood retention occur when arterial blood volume is at a minimum.