A patient-specific, finite element model for noncommunicating hydrocephalus capable of large deformation Joel A. Lefever a , José Jaime García b , Joshua H. Smith a,n a Department of Mechanical Engineering, Lafayette College, Easton, PA, USA b Escuela de Ingeniería Civil y Geomática, Universidad del Valle, Cali, Colombia article info Article history: Accepted 3 March 2013 Keywords: Noncommunicating hydrocephalus Nonlinear biphasic model Obstructive hydrocephalus abstract A biphasic model for noncommunicating hydrocephalus in patient-specific geometry is proposed. The model can take into account the nonlinear behavior of brain tissue under large deformation, the nonlinear variation of hydraulic conductivity with deformation, and contact with a rigid, impermeable skull using a recently developed algorithm. The model was capable of achieving over a 700 percent ventricular enlargement, which is much greater than in previous studies, primarily due to the use of an anatomically realistic skull recreated from magnetic resonance imaging rather than an artificial skull created by offsetting the outer surface of the cerebrum. The choice of softening or stiffening behavior of brain tissue, both having been demonstrated in previous experimental studies, was found to have a significant effect on the volume and shape of the deformed ventricle, and the consideration of the variation of the hydraulic conductivity with deformation had a modest effect on the deformed ventricle. The model predicts that noncommunicating hydrocephalus occurs for ventricular fluid pressure on the order of 1300 Pa. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Cerebrospinal fluid (CSF) plays an important role in the physiological activities and protection of the brain. Under the classical theory of cerebrospinal fluid hydrodynamics (Orešković and Klarica, 2011), this fluid is produced at a constant rate in the choroid plexuses of the lateral and third ventricles. Most of the CSF drains through the Sylvius aqueduct to the fourth ventricle, while a small amount flows through the cerebrum into the subarachnoid space adjacent to the skull. If the Sylvius aqueduct becomes obstructed, such as caused by a growing tumor adjacent to it, CSF accumulates in the ventricles and an abnormally high trans- mantle pressure gradient develops. As a result, the ventricles expand significantly, leading to a medical condition known as noncommunicating, or obstructive, hydrocephalus (Corns and Martin, 2012). Over the past 25 years, numerous mathematical models have been proposed to analyze hydrocephalus. Many of these models have represented the brain as a single-phase material in planar geometries (Fritz and Drapaca, 2009; Roy et al., 2013) and in cylindrical geometries (Drapaca et al., 2006; Sivaloganathan et al., 2005a, 2005b; Wilkie et al., 2010, 2011, 2012a, 2012b). In contrast, since the brain is immersed in and permeated by the CSF, others have represented the brain as a poroelastic or biphasic material in planar geometries (Momjian and Bichsel, 2008; Nagashima et al., 1987; Peña et al., 1999; Shahim et al., 2010; Taylor and Miller, 2004), in cylindrical geometries (Kaczmarek et al., 1997; Stastna et al., 1999; Tenti et al., 1999; Wilkie et al., 2012b), and in spherical geometries (García and Smith, 2010; Levine, 1999; Mehrabian and Abousleiman, 2011; Shahim et al., 2012; Smillie et al., 2005; Sobey and Wirth, 2006; Tully and Ventikos, 2009, 2011; Vardakis et al., 2013; Wilkie et al., 2012c). However, as the ventricles are not well represented as cylindrical or spherical cavities, recent efforts have focused on modeling hydrocephalus in anatomically realistic geometries (Cheng and Bilston, 2010; Clatz et al., 2007; Dutta- Roy et al., 2008) or quasi-realistic geometries (Wirth and Sobey, 2006). While many of these models have given relatively good correlations of clinical observations of hydrocephalus, only a few single-phase models (Drapaca et al., 2006; Fritz and Drapaca, 2009; Roy et al., 2013; Wilkie et al., 2011) and two biphasic models (Dutta-Roy et al., 2008; García and Smith, 2010) have considered the nonlinear stress–strain response documented experimentally under finite deformation (Franceschini et al., 2006; Kaster et al., 2011; Miller, 1999; Miller and Chinzei, 1997, 2002). Considering that displacements occurring during hydro- cephalus can be large, it would appear that nonlinear stress–strain curves under finite deformations should be taken into account. However, despite accounting for such behavior, the biphasic, noncommunicating model of Dutta-Roy et al. (2008) was not Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbiomech.2013.03.008 n Corresponding author. Tel.: þ1 610 330 5938. E-mail address: smithjh@lafayette.edu (J.H. Smith). Please cite this article as: Lefever, J.A., et al., A patient-specific, finite element model for noncommunicating hydrocephalus capable of large deformation. Journal of Biomechanics (2013), http://dx.doi.org/10.1016/j.jbiomech.2013.03.008i Journal of Biomechanics ∎ (∎∎∎∎) ∎∎∎–∎∎∎