Copyright © 2010 by ASME 1 ABSTRACT Syringomyelia (SM) is a neurological disease in which a fluid- filled cystic cavity, or syrinx, forms in the spinal cord (SC) resulting in progressive loss of sensory, motor functions, and/or pain in the patient. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure distribution and absorption in the subarachnoid space (SAS), resulting from a CSF flow blockage (stenosis), could be a key etiological factor for syrinx pathogenesis. In particular, the magnitude of the abrupt SAS pressure waves produced during coughing has been correlated with headache and pain in the patient. To better understand the influence of coughing on the spinal SAS, four axisymmetric fluid-structure interaction (FSI) in silico models representative of various conditions associated with SM were constructed. Each of the models was subjected to a cough-like CSF pressure pulse. The CSF flow stenosis was shown to attenuate and decelerate the CSF wave propagation in the SAS. The spinal SAS distensibility was also shown to have significant influence on the wave propagation. The in silico pressure results were found to be in agreement with a set of similar in vitro experiments [1]. Keywords: Syringomyelia, Chiari malformation, fluid-structure interaction, cerebrospinal fluid, Bio-fluid mechanics, subarachnoid space, syrinx, in silico model, computational fluid dynamics. INTRODUCTION As a neurological condition, SM has been recognized for over 130 years. Neurosurgeons have devised many hypotheses for the pathogenesis of SM primarily being rooted in abnormal hydrodynamics caused by CSF flow stenosis. In recent years engineers have made contributions by performing in silico [2, 3] and in vitro [1, 4, 5] simulations of SM with particular focus on biomechanical forces. While the in vitro models have provided detailed information on the CSF pressure and flow and spinal cord movement, they required construction of specific models for each mechanism. The in silico models have provided detailed information about the FSI of the spinal cord, stenosis, and CSF flow, but lacked experimental validation. Thus, the present in silico models were designed to be nearly identical to the in vitro models constructed by Martin et al. [1, 5] for validation of the computational results. METHODS Four in silico models were constructed in ANSYS (ANSYS Inc., Canonsburg, PA) ( Fig. 1). The model dimensions were based on an in vitro study by Martin et al. [1]. To simulate the cough excitation, a 5ms 100 mmHg pressure pulse was applied on the caudal end of the SAS (top side of Fig. 1). The four models were the following: 1. stenosis and syrinx experiment model (SSE): representative of a SM patient with a moderate sized syrinx and a spinal stenosis with a nearly rigid dura (modeled as glass). 2. stenosis and syrinx experiment with distensible spinal column (SSED): similar to SSE but with flexible and thicker dura. 3. stenosis removed experiment (SRE): similar to SSE, but with the stenosis removed. 4. stenosis removed experiment with distensible spinal column (SRED): similar to SRE, but with a thick and flexible dura. The axisymmetric models were constructed in ANSYS to represent the SM pathology where the CSF was contained between the spinal cord and dura mater. A cylindrical fluid-filled syrinx was located in the center of the spinal cord. A 2 cm length stenosis blocked >90% of the SAS area near the midsection of the syrinx cavity. RESULTS Wave propagation speed in the SAS and syrinx varied widely between each model both temporally and spatially (Fig. 2). The cough pressure excitation was administered at 0 cm (top of Fig. 2) and traveled through the spinal SAS to the rostral end (bottom of Fig. 2). Proceedings of the ASME 2010 Summer Bioengineering Conference (SBC2010) June 16-19, Grande Beach Resort, Naples Florida, USA A FLUID STRUCTRURE INTERACTION SIMULATION OF THE CEREBROSPINAL FLUID, SPINAL CORD, AND SPINAL STENOSIS PRESENT IN SYRINGOMYELIA Yifei Liu 1 , Bryn A. Martin 2 , Thomas J. Royston 1,3 , Francis Loth 4 1 Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 2 École Polytechnique Fédérale de Lausanne, Integrative Bioscience Institute, Lausanne, Switzerland 3 Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 4 Department of Mechanical Engineering, University of Akron, Akron, OH SBC2010-19433