BackgroundCerebrospinal fluid (CSF) is thought to flow into the brain via perivascular spaces around arteries, where it mixes with interstitial fluid. The precise details concerning fluid outflow remain controversial. Although fluid dynamics have been studied in the brain, little is known about spinal cord fluid inflow and outflow. Understanding the normal fluid physiology of the spinal cord may give insight into the pathogenesis of spinal cord oedema and CSF disorders such as syringomyelia. We therefore aimed to determine the fluid outflow pathways in the rat spinal cord.MethodsA fluorescent tracer, Alexa-Fluor®-647 Ovalbumin, was injected into the extracellular space of either the cervicothoracic lateral white matter or the grey matter in twenty-two Sprague–Dawley rats over 250 s. The rats were sacrificed at 20 or 60 min post injection. Spinal cord segments were sectioned and labelled with vascular antibodies for immunohistochemistry.ResultsFluorescent tracer was distributed over two to three spinal levels adjacent to the injection site. In grey matter injections, tracer spread radially into the white matter. In white matter injections, tracer was confined to and redistributed along the longitudinal axonal fibres. Tracer was conducted towards the pial and ependymal surfaces along vascular structures. There was accumulation of tracer around the adventitia of the intramedullary arteries, veins and capillaries, as well as the extramedullary vessels. A distinct layer of tracer was deposited in the internal basement membrane of the tunica media of arteries. In half the grey matter injections, tracer was detected in the central canal.ConclusionsThese results suggest that in the spinal cord interstitial fluid movement is modulated by tissue diffusivity of grey and white matter. The central canal, and the compartments around or within blood vessels appear to be dominant pathways for fluid drainage in these experiments. There may be regional variations in fluid outflow capacity due to vascular and other anatomical differences between the grey and white matter.
BACKGROUND Three-dimensional (3D) visualization of the neurovascular structures has helped preoperative surgical planning. 3D printed models and virtual reality (VR) devices are 2 options to improve 3D stereovision and stereoscopic depth perception of cerebrovascular anatomy for aneurysm surgery. OBJECTIVE To investigate and compare the practicality and potential of 3D printed and VR models in a neurosurgical education context. METHODS The VR angiogram was introduced through the development and testing of a VR smartphone app. Ten neurosurgical trainees from Australia and New Zealand participated in a 2-part interactive exercise using 3 3D printed and VR angiogram models followed by a questionnaire about their experience. In a separate exercise to investigate the learning curve effect on VR angiogram application, a qualified neurosurgeon was subjected to 15 exercises involving manipulating VR angiograms models. RESULTS VR angiogram outperformed 3D printed model in terms of resolution. It had statistically significant advantage in ability to zoom, resolution, ease of manipulation, model durability, and educational potential. VR angiogram had a higher questionnaire total score than 3D models. The 3D printed models had a statistically significant advantage in depth perception and ease of manipulation. The results were independent of trainee year level, sequence of the tests, or anatomy. CONCLUSION In selected cases with challenging cerebrovascular anatomy where stereoscopic depth perception is helpful, VR angiogram should be considered as a viable alternative to the 3D printed models for neurosurgical training and preoperative planning. An immersive virtual environment offers excellent resolution and ability to zoom, potentiating it as an untapped educational tool.
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