The Impact of Spinal Cord Nerve Roots and Denticulate Ligaments on Cerebrospinal Fluid Dynamics in the Cervical Spine

Abstract

Cerebrospinal fluid (CSF) dynamics in the spinal subarachnoid space (SSS) have been thought to play an important pathophysiological role in syringomyelia, Chiari I malformation (CM), and a role in intrathecal drug delivery. Yet, the impact that fine anatomical structures, including nerve roots and denticulate ligaments (NRDL), have on SSS CSF dynamics is not clear. In the present study we assessed the impact of NRDL on CSF dynamics in the cervical SSS. The 3D geometry of the cervical SSS was reconstructed based on manual segmentation of MRI images of a healthy volunteer and a patient with CM. Idealized NRDL were designed and added to each of the geometries based on in vivo measurments in the literature and confirmation by a neuroanatomist. CFD simulations were performed for the healthy and patient case with and without NRDL included. Our results showed that the NRDL had an important impact on CSF dynamics in terms of velocity field and flow patterns. However, pressure distribution was not altered greatly although the NRDL cases required a larger pressure gradient to maintain the same flow. Also, the NRDL did not alter CSF dynamics to a great degree in the SSS from the foramen magnum to the C1 level for the healthy subject and CM patient with mild tonsillar herniation (∼6 mm). Overall, the NRDL increased fluid mixing phenomena and resulted in a more complex flow field. Comparison of the streamlines of CSF flow revealed that the presence of NRDL lead to the formation of vortical structures and remarkably increased the local mixing of the CSF throughout the SSS.

Characterization of the Discrepancies Between Four-Dimensional Phase-Contrast Magnetic Resonance Imaging and In-Silico Simulations of Cerebrospinal Fluid Dynamics

“…MRI data acquisition was performed as previously described [19], In brief, MRI measurements were acquired on a 1.5-Tesla MRI (Achieva 2.6, Philips, Best, The Netherlands) with a standard 16-channel head and neck coil. A retrospective electrocardiogramtriggered, T1-weighted, segmented gradient echo sequence (Tl-TFE) with isotropic 1.5 mm voxel size was used for the 4D PCMRI measurements.…”

“…Size and placement of NRDL within the spinal canal were obtained from anatomical data found in literature [22][23][24] and visual inspection of the highresolution MRI images (average thickness of nerve rootlets and den ticulate ligaments were 1.4 and 0.1 mm, respectively). More details about this process is described by Pahlavian et al [19]. CFD Simulations.…”

“…CFD Simulations. CFD simulations were carried out based on the methodology and setup described previously [19]. In brief, a nonuniform unstructured rigid-walled computational mesh was generated for the healthy and patient geometry using ansys icem cfd (version 14.0, ANSYS Inc., Canonsburg, PA), ansys fluent (version 14.0, ANSYS Inc., Canonsburg, PA) was used to carry out the CFD simulations.…”

“…A review of CSF flow studies using CFD was published by Shaffer et al [20] and Yiallourou et al [21], A subject-specific CFD model of the cervical SSS CSF flow was developed by our research group with idealized spinal cord NRDL [19]. This study showed that NRDL has an important impact on CSF dynamics in terms of velocity field and flow patterns.…”

“…CFD has been applied in models with varying degrees of ana tomical complexity to help understand the underlying physiology of CSF flow [17][18][19]. A review of CSF flow studies using CFD was published by Shaffer et al [20] and Yiallourou et al [21], A subject-specific CFD model of the cervical SSS CSF flow was developed by our research group with idealized spinal cord NRDL [19].…”