Presenter: Brian Sweetman Date: September 13, 2006 Advisor: Andreas Linninger, PhD.

1. Quantification of Ventricular Enlargement Under Normal and Hydrocephalic Conditions Using Finite Element Methods Presenter: Brian Sweetman Date: September 13, 2006 Advisor: Andreas Linninger, PhD.

2. Outline of Talk Introduction • Importance of CSF and description of intracranial dynamics • Comparison of normal versus hydrocephalic cerebral spinal fluid (CSF) flow dynamics New theories and tools to verify them • Use of computational fluid dynamics to better understand communicating hydrocephalus • CFD to verify new theories describing hydrocephalus • Goals to improve current treatment Results using finite element modeling • Linear elastic case studies • Porous studies Conclusions Future case studies

3. CSF pathways in the human brain Importance of CSF • Reduces brain weight by 97% • Dampens effects of extra-cranial and intra-cranial forces (acts as cushion) • Transports nutrients important for brain and body function http://nyneurosurgery.org/hydro_3rdv.htm

4. Intracranial Dynamics Intracranial dynamics (ICD)—interaction between the solid brain, cerebral spinal fluid (CSF), and blood flow SAS Lateral ventricles • - CSF flows through ventricles, cerebral and spinal SAS, and the porous parenchyma in a pulsatilemanner • Dynamics of blood and CSF flow result in deformation of brain tissue • MRI provides an incomplete intracranial dynamics profile Goal: use computational fluid dynamics (CFD) to quantify what was previously only understood qualitatively using MRI parenchyma

5. Normal CSF Flow Dynamics • Produced in choroid plexus (500ml/24hr) • Reabsorbed by capillaries—Starling principle • No evidence to support absorption through pacchionian granulations • Windkessel mechanism • Energy from CSF pulse pressure absorbed by compliant arteries • Compliance=dV/dP • Constant non-pulsatile CSF flow in capillaries

6. CSF flow in the hydrocephalic case Decreased compliance (dV/dP) of arteries leading to greater CSF pulse pressure and enlargement of ventricles

7. Hydrocephalus Types • Acute: obstructive and non-communicating • Chronic: obstructive or communicating; both marked by decrease in intracranial compliance and increased capillary pulsations Symptoms • Abnormal accumulation of CSF • Ventricular enlargement and compression of the parenchyma • Increased Intracranial Pressure (ICP) in non-communicating • Headache, nausea, balance and vision problems, many others Treatments • Pressure shunt and catheter • Third ventriculostomy • Posterior fossa decompression (removal of matter to allow free flow of fluid through foramen magnum; seen in Chiari malformations)

8. CFD in the Study of Hydrocephalus • Quantify observations from clinical analysis • Construct patient intracranial dynamics (ICD) model based on actual deformations observed through MRI or other imaging techniques • Quantify CSF flow: flow rates, pressures • Understand causes of ventricular enlargement • Treat hydrocephalus by • More precise application (location/design) of shunt implantation • Better understanding of changes in ICD due to shunt • Alleviate the economic and medical cost of Hydrocephalus

9. Brain slice modeled as 2-D linear elastic (LE) Young’s modulus of white and gray matter included Pressure applied within “ventricle” Prior Research Stress profile of LE brain model

10. Movie displaying relative displacement of white (green) and grey (red) brain matter • White matter is more easily displaced due to a lower Young’s modulus compared to grey matter.

11. Pulsating CSF flow from Choroid plexus • Proposed Case study • Apply a pressure pulse to model the increased CSF pulse pressure acting on the wall of the lateral ventricle • Assumptions: high brain plasticity, low poisson ratio (~0) • Hypothesis: will see ventricular enlargement over time like that of the “balloon experiment” (Linninger, 2004) and test Greitz’s hypothesis that high brain plasticity explains why the ventricles deform overtime.

12. Porous Brain Model • Brain tissue is porous consisting of CSF pathways and interstitial fluid • Requires a porous fluid structure interaction (FSI) model • Brain modeled as a fluid-filled sponge • Brain tissue composed of multiple components • Somas (gray matter) • Axons (white matter) • Presence of pulsating arteries and blood/CSF mixing • Impose boundary conditions such as pulsating flow from choroid plexus and permeability into porous parenchyma • Quantify ventricular enlargement due to • Pulse pressure • Influence of spinal cord • Verify results by comparing with MRI flow data • patient specific geometry needed for more accurate results

13. Current and Future Case Studies Intracranial dynamics under normal conditions Linear Elastic Case Studies • LE brain model without deformation in prepontine area* • Same as above with deformation in prepontine area* • Add spinal cord • Differentiation b/w white and gray matter Porous Case Studies 5. Porous brain models as in 1 and 2 above* 6. As in 4 above but with spinal cord 7. Differentiation between white and gray matter Intracranial dynamics under hydrocephalic conditions • Impose obstruction(s) in flow field to induce hydrocephalus (monroe, aqueduct, etc) • Apply “pulse wave”; increased choroid plexus pulse pressure boundary condition to induce enlarged ventricles • Quantify/predict changes in intracranial dynamics due to shunt *Files have been created; needs to be ran and analyzed

14. References • Linninger, Andreas A., et al. "Cerebrospinal Fluid Flow in the Normal and Hydrocephalic Human Brain." IEEE Transaction on Biomedical Engineering (2006). • Linninger, Andreas A, et al. “Pulsatile cerebrospinal fluid dynamics in the human brain.” IEEE Transactions on Biomedical Engineering, 2005; 52:557-565. • Pena, Alonso, et al. "Finite Element Modeling of Progressive Ventricular Enlargement in Communicating Hydrocephalus.” (2002) • Greitz, Dan. “Radiological assessment of hydrocephalus: new theories and implications for therapy.” Neurosurgery Review (2004) 27: 145-165. • Egnor, Michael, et al. “A Model of Pulsations in Communicating Hydrocephalus.” Pediatric Neurosurgery, 2002; 36:281-303.

15. Acknowledgments • Andreas Linninger, PhD, Department of Biological and Chemical Engineering, University of Illinois at Chicago • Michalis Xenos, PhD, University of Illinois at Chicago • Kirstin Tawse, REU, Penn State University