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A unifying hypothesis for hydrocephalus, Chiari malformation, syringomyelia, anencephaly and spina bifida.

Williams H - Cerebrospinal Fluid Res (2008)

Bottom Line: This occurs because veins are compressible and a CNS volume increase may result in reduced venous blood flow.The flow of CSF has a beneficial effect on venous drainage.Conversely, obstruction to CSF flow causes localised pressure increases, which have an adverse effect on venous drainage.The Chiari malformation is associated with hindbrain herniation, which may be caused by low spinal pressure relative to cranial pressure.

View Article: PubMed Central - HTML - PubMed

Affiliation: 19 Elibank Road, Eltham, London, SE9 1QQ, UK. hfw@dircon.co.uk.

ABSTRACT
This work is a modified version of the Casey Holter Memorial prize essay presented to the Society for Research into Hydrocephalus and Spina Bifida, June 29th 2007, Heidelberg, Germany. It describes the origin and consequences of the Chiari malformation, and proposes that hydrocephalus is caused by inadequate central nervous system (CNS) venous drainage. A new hypothesis regarding the pathogenesis, anencephaly and spina bifida is described.Any volume increase in the central nervous system can increase venous pressure. This occurs because veins are compressible and a CNS volume increase may result in reduced venous blood flow. This has the potential to cause progressive increase in cerebrospinal fluid (CSF) volume. Venous insufficiency may be caused by any disease that reduces space for venous volume. The flow of CSF has a beneficial effect on venous drainage. In health it moderates central nervous system pressure by moving between the head and spine. Conversely, obstruction to CSF flow causes localised pressure increases, which have an adverse effect on venous drainage.The Chiari malformation is associated with hindbrain herniation, which may be caused by low spinal pressure relative to cranial pressure. In these instances, there are hindbrain-related symptoms caused by cerebellar and brainstem compression. When spinal injury occurs as a result of a Chiari malformation, the primary pathology is posterior fossa hypoplasia, resulting in raised spinal pressure. The small posterior fossa prevents the flow of CSF from the spine to the head as blood enters the central nervous system during movement. Consequently, intermittent increases in spinal pressure caused by movement, result in injury to the spinal cord. It is proposed that posterior fossa hypoplasia, which has origins in fetal life, causes syringomyelia after birth and leads to damage to the spinal cord in spina bifida. It is proposed that hydrocephalus may occur as a result of posterior fossa hypoplasia, where raised pressure occurs as a result of obstruction to flow of CSF from the head to the spine, and cerebral injury with raised pressure occurs in anencephaly by this mechanism.The current view of dysraphism is that low central nervous system pressure and exposure to amniotic fluid, damage the central nervous system. The hypothesis proposed in this essay supports the view that spina bifida is a manifestation of progressive hydrocephalus in the fetus. It is proposed that that mesodermal growth insufficiency influences both neural tube closure and central nervous system pressure, leading to dysraphism.

No MeSH data available.


Related in: MedlinePlus

A hypothetical graph showing the relation between spinal or cranial pressure, and venous volume, with and without Chiari malformation. CSF obstruction at the foramen magnum divides the CSF space into cranial and spinal compartments. The sum of the pressure volume indices of the two spaces would approximate that of the unobstructed CNS. The pressure response to influx of venous volume either in the head or the spine may be enhanced by the presence of Chiari malformation.
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Figure 2: A hypothetical graph showing the relation between spinal or cranial pressure, and venous volume, with and without Chiari malformation. CSF obstruction at the foramen magnum divides the CSF space into cranial and spinal compartments. The sum of the pressure volume indices of the two spaces would approximate that of the unobstructed CNS. The pressure response to influx of venous volume either in the head or the spine may be enhanced by the presence of Chiari malformation.

Mentions: CSF flow contributes to compliance by regulating the transluminal pressure of veins and therefore their patency and flow. Poiseuille's law states that laminar flow in a tube is inversely proportional to the fourth power of the radius. Hence a decrease in vessel diameter will cause a four-fold increase in resistance. If any pressure increase associated with increase in CNS volume is distributed throughout the intrathecal space, there will be a small average reduction in the diameter of many veins. If the whole CNS venous system is affected by a CNS volume increase, the overall reduction in venous outflow will be minimised, thus free flow of CSF facilitates venous drainage. Veins inside the head do not collapse when moving to an upright position because the movement of CSF with gravitational force allows both fluids to experience the same pressure gradient [10], maintaining the patency of veins. Obstruction to CSF flow at the foramen magnum is an important cause of reduced compliance. Movement of the body appears to contribute to foramen magnum obstruction, so that CSF flow may be affected by posture [8]. The head and spine may be transiently separated into compartments with reduced pressure volume indices. Evidence of obstruction may be present without an obvious hindbrain hernia [11,12] or with cerebellar deformity. Pressure gradients between the CSF spaces of the head and spine are normally those due to gravity [13]. In the presence of an obstruction associated with spina bifida or syringomyelia, pressure may fluctuate independently in the head and spine [8,14,15]. This phenomenon has been termed 'craniospinal pressure dissociation'. With normal CSF pathways at the foramen magnum, retrograde flow of venous blood into the CNS may be compensated by compression of distant veins. If a volume increase occurs in either the head or the spine in the presence of foramen magnum obstruction, it will, according to this hypothesis cause a pressure response which will be greater than if CSF pathways were unobstructed. It is proposed therefore that with Chiari malformation retrograde venous flow causes an enhanced pressure response, as illustrated in Fig. 2.


A unifying hypothesis for hydrocephalus, Chiari malformation, syringomyelia, anencephaly and spina bifida.

Williams H - Cerebrospinal Fluid Res (2008)

A hypothetical graph showing the relation between spinal or cranial pressure, and venous volume, with and without Chiari malformation. CSF obstruction at the foramen magnum divides the CSF space into cranial and spinal compartments. The sum of the pressure volume indices of the two spaces would approximate that of the unobstructed CNS. The pressure response to influx of venous volume either in the head or the spine may be enhanced by the presence of Chiari malformation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2365936&req=5

Figure 2: A hypothetical graph showing the relation between spinal or cranial pressure, and venous volume, with and without Chiari malformation. CSF obstruction at the foramen magnum divides the CSF space into cranial and spinal compartments. The sum of the pressure volume indices of the two spaces would approximate that of the unobstructed CNS. The pressure response to influx of venous volume either in the head or the spine may be enhanced by the presence of Chiari malformation.
Mentions: CSF flow contributes to compliance by regulating the transluminal pressure of veins and therefore their patency and flow. Poiseuille's law states that laminar flow in a tube is inversely proportional to the fourth power of the radius. Hence a decrease in vessel diameter will cause a four-fold increase in resistance. If any pressure increase associated with increase in CNS volume is distributed throughout the intrathecal space, there will be a small average reduction in the diameter of many veins. If the whole CNS venous system is affected by a CNS volume increase, the overall reduction in venous outflow will be minimised, thus free flow of CSF facilitates venous drainage. Veins inside the head do not collapse when moving to an upright position because the movement of CSF with gravitational force allows both fluids to experience the same pressure gradient [10], maintaining the patency of veins. Obstruction to CSF flow at the foramen magnum is an important cause of reduced compliance. Movement of the body appears to contribute to foramen magnum obstruction, so that CSF flow may be affected by posture [8]. The head and spine may be transiently separated into compartments with reduced pressure volume indices. Evidence of obstruction may be present without an obvious hindbrain hernia [11,12] or with cerebellar deformity. Pressure gradients between the CSF spaces of the head and spine are normally those due to gravity [13]. In the presence of an obstruction associated with spina bifida or syringomyelia, pressure may fluctuate independently in the head and spine [8,14,15]. This phenomenon has been termed 'craniospinal pressure dissociation'. With normal CSF pathways at the foramen magnum, retrograde flow of venous blood into the CNS may be compensated by compression of distant veins. If a volume increase occurs in either the head or the spine in the presence of foramen magnum obstruction, it will, according to this hypothesis cause a pressure response which will be greater than if CSF pathways were unobstructed. It is proposed therefore that with Chiari malformation retrograde venous flow causes an enhanced pressure response, as illustrated in Fig. 2.

Bottom Line: This occurs because veins are compressible and a CNS volume increase may result in reduced venous blood flow.The flow of CSF has a beneficial effect on venous drainage.Conversely, obstruction to CSF flow causes localised pressure increases, which have an adverse effect on venous drainage.The Chiari malformation is associated with hindbrain herniation, which may be caused by low spinal pressure relative to cranial pressure.

View Article: PubMed Central - HTML - PubMed

Affiliation: 19 Elibank Road, Eltham, London, SE9 1QQ, UK. hfw@dircon.co.uk.

ABSTRACT
This work is a modified version of the Casey Holter Memorial prize essay presented to the Society for Research into Hydrocephalus and Spina Bifida, June 29th 2007, Heidelberg, Germany. It describes the origin and consequences of the Chiari malformation, and proposes that hydrocephalus is caused by inadequate central nervous system (CNS) venous drainage. A new hypothesis regarding the pathogenesis, anencephaly and spina bifida is described.Any volume increase in the central nervous system can increase venous pressure. This occurs because veins are compressible and a CNS volume increase may result in reduced venous blood flow. This has the potential to cause progressive increase in cerebrospinal fluid (CSF) volume. Venous insufficiency may be caused by any disease that reduces space for venous volume. The flow of CSF has a beneficial effect on venous drainage. In health it moderates central nervous system pressure by moving between the head and spine. Conversely, obstruction to CSF flow causes localised pressure increases, which have an adverse effect on venous drainage.The Chiari malformation is associated with hindbrain herniation, which may be caused by low spinal pressure relative to cranial pressure. In these instances, there are hindbrain-related symptoms caused by cerebellar and brainstem compression. When spinal injury occurs as a result of a Chiari malformation, the primary pathology is posterior fossa hypoplasia, resulting in raised spinal pressure. The small posterior fossa prevents the flow of CSF from the spine to the head as blood enters the central nervous system during movement. Consequently, intermittent increases in spinal pressure caused by movement, result in injury to the spinal cord. It is proposed that posterior fossa hypoplasia, which has origins in fetal life, causes syringomyelia after birth and leads to damage to the spinal cord in spina bifida. It is proposed that hydrocephalus may occur as a result of posterior fossa hypoplasia, where raised pressure occurs as a result of obstruction to flow of CSF from the head to the spine, and cerebral injury with raised pressure occurs in anencephaly by this mechanism.The current view of dysraphism is that low central nervous system pressure and exposure to amniotic fluid, damage the central nervous system. The hypothesis proposed in this essay supports the view that spina bifida is a manifestation of progressive hydrocephalus in the fetus. It is proposed that that mesodermal growth insufficiency influences both neural tube closure and central nervous system pressure, leading to dysraphism.

No MeSH data available.


Related in: MedlinePlus