The importance of the cortical subarachnoid space in understanding hydrocephalus

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>In this paper the authors define the role of the cortical subarachnoid space (CSAS) in poorly understood forms of hydrocephalus to cerebrospinal fluid (CSF) dynamics to improve understanding of the importance of the CSAS and its role in selecting patients for endoscopic third ventriculostomy (ETV). The secondary purpose of this work was to define testable hypotheses to explain enigmatic disorders of CSF dynamics and to suggest how these concepts could be tested.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>The magnitude of the contribution of the CSAS is explored using the solid geometry of concentric spheres. With this starting point, clinical conditions in which CSF dynamics are not easily understood are explored regarding the potential role of the CSAS. Overall, problems of CSF dynamics are easily understood. Insights may be gained when the results of a pathological process or its treatment vary from what has been expected.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Acute changes in ventricular volume at the time that hydrocephalus develops, the failure of shunts, and the changes in ventricular volume with shunt repair may occur very rapidly. Changes in the volume of water in the brain, especially in the brain substance itself, are unlikely to occur at this rapid rate and may be interpreted as a simple redistribution of the CSF between the ventricle and CSAS with no initial change in the actual volume of brain parenchyma. Problems such as pseudotumor cerebri, shunt failure with nonresponsive ventricles, and negative-pressure hydrocephalus can be explained by assessing the ability of ventricular CSF to flow to the CSAS and the ability of this fluid to exit this compartment. Ventricular enlargement at the time of shunt failure implies a failure of flow between the ventricles and CSAS, implying that all patients who show this phenomenon are potential candidates for ETV.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The important role of the CSAS in the pathophysiology of various forms of hydrocephalus has been largely ignored. Attention to the dynamics of the CSF in this compartment will improve understanding of enigmatic conditions of hydrocephalus and improve selection criteria for treatment paradigms such as ETV. These concepts lead to clearly defined problems that may be solved by the creation of a central database to address these issues.</jats:p></jats:sec>

Higher Failure of Endoscopic Third Ventriculostomy in Infants: The “Distensible” Skull Is the Culprit

“…This positive contribution to an effective CSF flow is counteracted by the distensible head. Our case demonstrates that an increase of the stiffness of the system (which in our patient occurred after maturation of the skull) could maximize the positive elastance effects of the ETV on the CSF flow [4, 10]. Moreover, a stiffer head would increase the average pressure gradient between the cortical subarachnoid spaces and the venous sinuses, ensuring greater CSF clearance.…”

“…These factors are critical to assess the likelihood of the success of the ETV, as obstructive etiology and older age are associated with better results after ETV. Although several studies have shown that the risk of immediate ETV failure is higher in infants than in older babies, the reasons behind these difference are under debate [4, 5]. We describe a case which may suggest that the presence of a “distensible” skull and the lack of an adequate pressure gradient may be the main reason for the higher ETV failure in infants.…”

A consensus on the classification of hydrocephalus: its utility in the assessment of abnormalities of cerebrospinal fluid dynamics

“…What followed has been a 30-year study of hydrocephalus based on this model. It became evident to me that this model would be useful in the classification of hydrocephalus and formed the basis of the book chapter that was produced [13, 15].

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A lesson in history: the evolution of endoscopic third ventriculostomy

“…18 Rekate explains that the fundamental criterion of successful patient selection for an ETV is an obstruction between the third ventricle and the cortical subarachnoid spaces. Building on "the importance of the cortical subarachnoid space in understanding hydrocephalus," Rekate et al 19 released a report of precisely that title in 2008 that beautifully describes CSF dynamics, specifically regarding the role the often ignored cortical subarachnoid space plays in various forms of hydrocephalus.…”