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  • The Role of the Pia Mater in Controlling Brain and Spinal Cord Intraparenchymal Pressure

    Final Number:

    Daniel Harwell MD; Justin Louis Gibson; Richard D. Fessler MD; Jeffrey R. Holtz P.A.-C.; David B. Pettigrew MS PhD; Charles Kuntz, IV MD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2015 Annual Meeting

    Introduction: Several multicenter randomized control trials have shown that decompression with durotomy/duroplasty significantly decreases intracranial pressure (ICP), improving mortality. Currently, decompressive craniectomy combined with augmentative duraplasty is widely performed and is recommended by most authors. However, there is a paucity of evidence regarding the effectiveness of decompression of the spinal cord by meningoplasty.

    Methods: The supratentorial brain and spinal cord were carefully removed from four fresh cadavers. The dura and arachnoid mater investments were removed. ICP monitors were placed bilaterally in the frontal and parietal lobes, as well as the cervical and thoracic spinal cord. The specimens were then submerged in a hypotonic solution and intraparenchymal pressures were monitored over 5 days. After 5 days, a complete dorsal midline piotomy was made on the spinal cord and the final pressures were recorded.

    Results: Both the brains and spinal cords showed marked swelling. Preliminary data show that there is a slight but statistically significant increase in brain IPP (avg. for all 4 lobes = 4 mm Hg). Spinal cord IPP began to rise within an average of 90 minutes. Average peak spinal cord IPP was 61 (cervical) and 43 (thoracic) mm Hg. After the dorsal midline piotomy, the IPPs decreased immediately to nearly their baseline values.

    Conclusions: The simulated edema model has differential effects on brain and spinal cord IPP. Brain IPP increased only slightly, consistent with the model that increased intracranial pressure is primarily due to constraints imposed by the cranium and dura mater. In contrast, spinal cord IPP increased substantially. Piotomy immediately and dramatically reduced spinal cord IPP. These data are consistent with the hypothesis that intramedullary pressure is primarily due to constraints imposed by the pia mater. Conversely, we hypothesize that the brain sulci permit the pia-invested brain to better accommodate edema without significant increases in IPP.

    Patient Care: While this is a basic science project our hope is that this project will further the understanding of the physiology of the spinal cord, specifically the role of the meninges. The pia appears to play a key role in modulating intraparenchymal pressure. Our hope is that, with further research, this knowledge can be applied to a surgical procedure to hopefully improve outcome in patients with spinal cord injury.

    Learning Objectives: By the conclusion of this session, participants should be able to 1) Discuss a novel method for modeling neural edema. 2) Describe the contribution of the pia mater to spinal cord intraparenchymal pressure. 3) Understand how piotomy can ameliorate IPP in this model.


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