(171f) Ventricular Wall Contact and Its Role in Flow Disruption in Hydrocephalus Treatment

Hydrocephalus is characterized by the accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain. Treating this neurological disorder involves the implantation of a silicone ventricular catheter (VC) into the ventricles to drain the fluid into the plural, atrial, or peritoneal cavity. However, the ventricular catheter (VC) failure rate is 50% within two years^1,2 due to mechanical obstructions of the drainage holes caused by tissue obstruction and cellular adhesion in hydrocephalic ventricles. Incremental progress has been made with VC design apart from antibiotic impregnation to prevent bacterial cell accumulation, but the failure rate continues to remain unacceptably high. Prior work using computational fluid dynamics (CFD) has used a makeshift rectangular box to replicate a hydrocephalic ventricle^-3-6. Given the dynamic nature of ventricular morphology, a box lacks the complexity necessary to accurately depict the intricate relationship between CSF flow in the ventricles and through the ventricular catheter under unstable physiological flow conditions. By employing ANSYS Fluent computational fluid dynamics, we conducted a comprehensive analysis to explore how cerebrospinal fluid flow is influenced by patient-specific morphological changes in hydrocephalic ventricles under pathophysiological disease conditions such as hydrocephalus.

Deidentified, patient-specific^7,8 MRI and CT scans were used from our collaborative medical centers at Children's Hospital of Michigan and Children's Hospital of Alabama to create 3D ventricular renders for CFD simulation. Ventricular catheters were inserted into the lateral ventricles using anterior and posterior trajectories. Physiological boundary conditions such as CSF secretion, heart rate, respiration, and intracranial pressure were assigned to the ventricular domain with a constant pressure outlet at the VC exit. A laminar steady state flow model was implemented with boundary layers placed at all VC walls to capture near wall dynamics. Body specific meshing was implemented to ensure fine mesh transition between ventricular free stream and near field VC volume domains. Flow parameters, including mass flow rate, shear stress contours, pressure gradients, and velocity streamlines, were quantified in the catheter drainage holes and lumen. Comparative analysis was performed using uniform, smooth-transition, and aspect ratio boundary layers to compare near wall CSF behavior for numerical accuracy.

Simulation results showed no changes in mass flow rates and shear contours for catheters inserted into posterior trajectories regardless of ventricular size and morphology. However, a significant decrease in mass flowrate and shear stress was observed in VC models inserted in the anterior trajectories as a result of contact between the ventricular wall and the surface of the VC for smaller ventricles. Near wall analysis showed increasing eddy mixing as the ventricular wall approached the VC surface, resulting in more turbulent flow conditions at the surface of the VC. Patients with more complex ventricular shapes displayed more complex mixing streamlines at the VC surface interface than symmetric ventricular morphologies. Future work will address the effect of variable CSF pulsatility⁹ on VC flow dynamics.

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