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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

Hypothetical graph showing the change in spinal volume and pressure with movement and a space-occupying lesion. Lines a and b represent volume fluctuation with movement, with 'a' representing the normal range and 'b' the range with an uncompensated space occupying lesion. Points 'a' and 'b' on the curve indicate maximal CSF pressures that occur with maximal venous volume.
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Figure 3: Hypothetical graph showing the change in spinal volume and pressure with movement and a space-occupying lesion. Lines a and b represent volume fluctuation with movement, with 'a' representing the normal range and 'b' the range with an uncompensated space occupying lesion. Points 'a' and 'b' on the curve indicate maximal CSF pressures that occur with maximal venous volume.

Mentions: That the degree of hindbrain herniation does not correlate with spinal injury in syringomyelia [35] and spina bifida, and posterior fossa size does not correlate with the degree of cerebellar herniation in Chiari I [11,12,36], indicates that factors other than posterior fossa hypoplasia are influencing the degree of neural injury. Herniation will relate to the degree to which skeletal defects lead to pressure changes and the extent to which low spinal pressure causes hindbrain herniation in any individual case. Both herniation and neural injury will depend upon an interaction between the anatomy of the posterior fossa and physiological influences on CSF pressure and flow. Although low pressure may contribute to the cause of hindbrain herniation, once herniation becomes more established CNS pressure will tend to vary more widely as the head and spine become separate compartments. Pressure in the head may tend to rise [2] due to a larger volume of neural tissue in the head than the spine, with a greater arterial supply, as illustrated by the caudal flow of CSF across the foramen magnum in systole and the rostral flow in diastole [37]. The potential range in pressure is arguably greatest in the spine because of the capacity and compressibility of the intraspinal venous plexus vessels. This theory asserts that the highest spinal pressures lead to cord ischemia and the lowest pressures contribute to maintaining the hindbrain herniation. Loss of neural tissue by ischemic atrophy will tend to benefit remaining cord or brain, whereas growth of neural tissue may perpetuate reduced compliance. A syrinx cavity forms a space-occupying lesion and so reduces compliance. The effect of a space-occupying lesion on spinal pressure will be as in Fig. 3. Benign lesions may be accommodated without pressure increase if neural or CSF volumes fall. The combination of pressure effects illustrated in Figs. 2 and 3 will be a left shift in the pressure volume curve in hydrocephalus.


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

Williams H - Cerebrospinal Fluid Res (2008)

Hypothetical graph showing the change in spinal volume and pressure with movement and a space-occupying lesion. Lines a and b represent volume fluctuation with movement, with 'a' representing the normal range and 'b' the range with an uncompensated space occupying lesion. Points 'a' and 'b' on the curve indicate maximal CSF pressures that occur with maximal venous volume.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Hypothetical graph showing the change in spinal volume and pressure with movement and a space-occupying lesion. Lines a and b represent volume fluctuation with movement, with 'a' representing the normal range and 'b' the range with an uncompensated space occupying lesion. Points 'a' and 'b' on the curve indicate maximal CSF pressures that occur with maximal venous volume.
Mentions: That the degree of hindbrain herniation does not correlate with spinal injury in syringomyelia [35] and spina bifida, and posterior fossa size does not correlate with the degree of cerebellar herniation in Chiari I [11,12,36], indicates that factors other than posterior fossa hypoplasia are influencing the degree of neural injury. Herniation will relate to the degree to which skeletal defects lead to pressure changes and the extent to which low spinal pressure causes hindbrain herniation in any individual case. Both herniation and neural injury will depend upon an interaction between the anatomy of the posterior fossa and physiological influences on CSF pressure and flow. Although low pressure may contribute to the cause of hindbrain herniation, once herniation becomes more established CNS pressure will tend to vary more widely as the head and spine become separate compartments. Pressure in the head may tend to rise [2] due to a larger volume of neural tissue in the head than the spine, with a greater arterial supply, as illustrated by the caudal flow of CSF across the foramen magnum in systole and the rostral flow in diastole [37]. The potential range in pressure is arguably greatest in the spine because of the capacity and compressibility of the intraspinal venous plexus vessels. This theory asserts that the highest spinal pressures lead to cord ischemia and the lowest pressures contribute to maintaining the hindbrain herniation. Loss of neural tissue by ischemic atrophy will tend to benefit remaining cord or brain, whereas growth of neural tissue may perpetuate reduced compliance. A syrinx cavity forms a space-occupying lesion and so reduces compliance. The effect of a space-occupying lesion on spinal pressure will be as in Fig. 3. Benign lesions may be accommodated without pressure increase if neural or CSF volumes fall. The combination of pressure effects illustrated in Figs. 2 and 3 will be a left shift in the pressure volume curve in hydrocephalus.

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