Ryan Glyn Jones

Aim: Chiari malformation and syringomyelia are disorders of cerebrospinal fluid (CSF) dynamics, yet translation of mechanistic insights into patient care is limited by the low prevalence and heterogeneity of human disease, and by methodological constraints of in-vivo CSF measurements. In Cavalier King Charles Spaniels (CKCS), these conditions are highly prevalent and represent a clinically relevant companion animal model. However, existing canine CSF flow studies rely largely on phase-contrast magnetic resonance imaging (MRI) metrics that incompletely characterize three-dimensional flow. This study aimed to develop a computational fluid dynamics (CFD) framework to characterise CSF flow dynamics in CKCS, providing a translational approach for investigating CSF dynamics in both veterinary and human cases. Methods: Retrospective MRI data from nine clinically normal CKCS were used to construct subject-specific craniospinal CSF geometries. CFD simulations yielded cardiac-driven oscillatory CSF motion under physiologically plausible boundary conditions, incorporating spinal compliance and zero net flow per cardiac cycle to characterize velocities and pressures. Results: Simulations revealed pulsatile, laminar CSF flow with pronounced regional heterogeneity, dominant subarachnoid space (SAS) transport, complex flow patterns within the cerebral aqueduct, and a cycle-dependent pressure difference between the central canal and SAS with marked sensitivity to anatomical location and downstream spinal geometry. Conclusion: These findings demonstrate that local anatomy strongly influences measured CSF velocities, limiting the translational reliability of isolated in vivo measurements while supporting CFD as a more robust framework for clinically meaningful interpretation. Establishing these baseline craniospinal flow characteristics provides a necessary reference for interpreting clinical CSF measurements and for extending computational analyses to dogs with Chiari-like malformation and syringomyelia.

Abstract Background: Syringomyelia (SM) is a disorder of cerebrospinal fluid (CSF) circulation strongly associated with Chiari-like malformation (CM) in Cavalier King Charles Spaniels (CKCS). Although CM is nearly ubiquitous in the breed, not all affected dogs develop signs of CM-related pain (CM-P) or Syringomyelia (SM), raising questions about underlying mechanisms. CM-P without SM has been linked to brachycephaly, whereas SM involves additional craniocervical conformational changes. This study tested whether CM-P affected CKCS with and without SM were more likely to have reduced cisterna magna volume and cervicothoracic subarachnoid space (SAS) narrowing compared to each other and with CKCS with CM but no clinical signs (CM-N). Results: A retrospective dataset of 168 CKCS was reviewed. After applying exclusion criteria and matching for body size, three groups were analysed: CM-N, CM-P without SM, and CM-P with SM (n = 10 per group). Three-dimensional SAS models from the foramen magnum to T3/T4 were generated by segmenting MRI data in 3D Slicer and lofting contours in ANSYS SpaceClaim. Whole SAS volume was lower in SM cases than in both comparison groups (ANOVA p = 0.0033, η² = 0.344). Cisterna magna volume and surface area did not differ, but the volume-to-surface area ratio was reduced in SM affected dogs (p = 0.011, η² = 0.274), consistent with a relatively constricted SAS. Slice-by-slice analysis revealed focal reductions in annular area and hydraulic diameter at the occiput, C2–C6, and T1–T3, with hydraulic diameter more sensitive to local change. Corresponding decreases in Womersley number indicated a viscous-dominated CSF flow regime and loss of pulsatile compliance. Principal Component Analysis confirmed distinct clustering of SM cases, while CM-P and CM-N dogs overlapped; displacement along the principal axis correlated with syrinx diameter, linking morphology to clinical severity. Conclusions: CKCS with CM-P and SM have global SAS volume loss with focal constrictions, whereas CKCS with CM-P without SM does not differ from CM-N. These findings support a model in which SM develops from limited cranial and spinal SAS capacity to accommodate and redistribute pulsatile CSF flow, altering pressure transmission along the neuraxis. The 3D reconstruction method offers a reproducible framework for quantifying these changes and linking structure to flow dynamics. Limitations include incomplete neuroaxis coverage, postSM analysis (cause versus effect), small sample size, and single-operator measurements. Keywords: Canine, Chiari-like malformation, Cerebrospinal fluid dynamics, Spinal Subarachnoid Space, Compliance, Cisterna magna, Annular area, Hydraulic diameter , Womersley number Computational modelling

Cerebrospinal fluid (CSF) plays a crucial role in maintaining brain homeostasis by facilitating the clearance of metabolic waste and regulating intracranial pressure. Dysregulation of CSF flow can lead to conditions like syringomy-elia, and hydrocephalus. This review details the anatomy of CSF flow, examining its contribution to waste clearance within the brain and spinal cord. The review integrates data from human, canine, and other mammalian studies, with a particular focus on brachycephalic dogs. Certain dog breeds exhibit a high prevalence of CSF-related conditions due to artificial selection for neotenous traits, making them valuable models for studying analogous human conditions, such as Chiari-like malformation and syringomyelia associated with craniosynostosis. This review discusses the anatomical features specific to some brachycephalic breeds and the impact of skull and cranial cervical conforma-tion on CSF flow patterns, providing insights into the pathophysiology and potential modelling approaches for these conditions.