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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

The intracranial pressure volume relationship: a graph depicting the effect on intracranial pressure of increasing volume. Central nervous system compliance depends upon intrathecal volume. Redrawn from [5], with permission [Additional file 1].
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Figure 1: The intracranial pressure volume relationship: a graph depicting the effect on intracranial pressure of increasing volume. Central nervous system compliance depends upon intrathecal volume. Redrawn from [5], with permission [Additional file 1].

Mentions: Blood from the CNS is drained by a venous plexus that is extensive, anastamotic and valveless. It allows blood to flow in a retrograde direction, away from the heart and into the CNS with postural movements [6,7]. CSF pressure fluctuations with movement have been observed directly [8] and small movements such as occur during speech, may cause detectable CNS pressure fluctuations [5]. Veins situated between the dura and surrounding bone are highly compressible and capable of large volume fluctuations [7]. Such veins are prominent in the spine, and are susceptible to volume fluctuation with alterations in body cavity pressure [7]. As CNS venous volume increases with retrograde flow veins may be distended due to 'back pressure' or may be compressed due to elevation of overall pressure, resistance to venous outflow then increases, outflow is reduced, and pressure will tend to rise. Pressure increase in response to increasing intrathecal volume corresponds to a phase of reduced compliance [5]. If volume increases further, a pressure may be reached which compromises arterial flow, resulting in ischemia of neural tissue [5]. The relationship between overall CNS pressure and added volume is shown in Fig. 1. The pressure volume index (PVI) is the volume that when added to the CSF space results in a ten-fold increase in pressure. The normal adult range is 13–26 ml [9]. Adults will have a larger PVI than infants because of a larger central nervous system with a correspondingly greater venous volume.


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

Williams H - Cerebrospinal Fluid Res (2008)

The intracranial pressure volume relationship: a graph depicting the effect on intracranial pressure of increasing volume. Central nervous system compliance depends upon intrathecal volume. Redrawn from [5], with permission [Additional file 1].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: The intracranial pressure volume relationship: a graph depicting the effect on intracranial pressure of increasing volume. Central nervous system compliance depends upon intrathecal volume. Redrawn from [5], with permission [Additional file 1].
Mentions: Blood from the CNS is drained by a venous plexus that is extensive, anastamotic and valveless. It allows blood to flow in a retrograde direction, away from the heart and into the CNS with postural movements [6,7]. CSF pressure fluctuations with movement have been observed directly [8] and small movements such as occur during speech, may cause detectable CNS pressure fluctuations [5]. Veins situated between the dura and surrounding bone are highly compressible and capable of large volume fluctuations [7]. Such veins are prominent in the spine, and are susceptible to volume fluctuation with alterations in body cavity pressure [7]. As CNS venous volume increases with retrograde flow veins may be distended due to 'back pressure' or may be compressed due to elevation of overall pressure, resistance to venous outflow then increases, outflow is reduced, and pressure will tend to rise. Pressure increase in response to increasing intrathecal volume corresponds to a phase of reduced compliance [5]. If volume increases further, a pressure may be reached which compromises arterial flow, resulting in ischemia of neural tissue [5]. The relationship between overall CNS pressure and added volume is shown in Fig. 1. The pressure volume index (PVI) is the volume that when added to the CSF space results in a ten-fold increase in pressure. The normal adult range is 13–26 ml [9]. Adults will have a larger PVI than infants because of a larger central nervous system with a correspondingly greater venous volume.

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