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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 simplified flow diagram representing the causes of hydrocephalus and syringomyelia.
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Figure 7: A simplified flow diagram representing the causes of hydrocephalus and syringomyelia.

Mentions: Surgery that improves CSF pathways at the foramen magnum may cause collapse of the syrinx cavity, improve cord blood flow and the clinical features of syringomyelia. This indicates that neural injury results from impaired flow of CSF at the foramen magnum [1,2]. The central canal of the cord forms a potential space, into which fluid from the parenchyma may pass, allowing the formation of separate cavities that characterise syringomyelia [78]. During physical exertion, movement of fluid within the syrinx cavity may weaken its walls causing it to have a greater capacity to enlarge [79,80] and during relaxation, the cavity will tend to fill. This may be facilitated by a hyperaemic response. Syringomyelia occurs in association with posterior fossa restriction of Chiari I and other causes of reduced CNS compliance, particularly if they directly affect the spine. Tumours, vertebral deformity and arachnoiditis may reduce space and CSF flow and may lead to the onset of cavity formation. Vertebral injury causing abnormal function of the spinal venous plexus may impair spinal venous drainage as a result of autonomic dysfunction [81]. Decompressing the cord ameliorates syringomyelia, and reducing the volume of fluid inside a syrinx cavity at operation may enhance the rate of any post-operative improvement [82]. Normal pressure hydrocephalus is an analogous disease process to syringomyelia, as has been argued elsewhere, [83] with differing distribution of excess extracellular fluid. Spinal cord oedema would, according to this theory, represent a pre-syrinx state [84]. Syringobulbia is the manifestation of raised spinal pressure with the unusual situation of fluid being able to track into the brain stem. Communicating syringomyelia would occur with pressure gradients and anatomy allowing flow from the fourth ventricle into the spine. A simplified representation of the mechanism for hydrocephalus and syringomyelia is shown in Fig. 7. Posterior fossa hypoplasia makes hydrocephalus and syringomyelia features of spina bifida after birth.


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

Williams H - Cerebrospinal Fluid Res (2008)

A simplified flow diagram representing the causes of hydrocephalus and syringomyelia.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: A simplified flow diagram representing the causes of hydrocephalus and syringomyelia.
Mentions: Surgery that improves CSF pathways at the foramen magnum may cause collapse of the syrinx cavity, improve cord blood flow and the clinical features of syringomyelia. This indicates that neural injury results from impaired flow of CSF at the foramen magnum [1,2]. The central canal of the cord forms a potential space, into which fluid from the parenchyma may pass, allowing the formation of separate cavities that characterise syringomyelia [78]. During physical exertion, movement of fluid within the syrinx cavity may weaken its walls causing it to have a greater capacity to enlarge [79,80] and during relaxation, the cavity will tend to fill. This may be facilitated by a hyperaemic response. Syringomyelia occurs in association with posterior fossa restriction of Chiari I and other causes of reduced CNS compliance, particularly if they directly affect the spine. Tumours, vertebral deformity and arachnoiditis may reduce space and CSF flow and may lead to the onset of cavity formation. Vertebral injury causing abnormal function of the spinal venous plexus may impair spinal venous drainage as a result of autonomic dysfunction [81]. Decompressing the cord ameliorates syringomyelia, and reducing the volume of fluid inside a syrinx cavity at operation may enhance the rate of any post-operative improvement [82]. Normal pressure hydrocephalus is an analogous disease process to syringomyelia, as has been argued elsewhere, [83] with differing distribution of excess extracellular fluid. Spinal cord oedema would, according to this theory, represent a pre-syrinx state [84]. Syringobulbia is the manifestation of raised spinal pressure with the unusual situation of fluid being able to track into the brain stem. Communicating syringomyelia would occur with pressure gradients and anatomy allowing flow from the fourth ventricle into the spine. A simplified representation of the mechanism for hydrocephalus and syringomyelia is shown in Fig. 7. Posterior fossa hypoplasia makes hydrocephalus and syringomyelia features of spina bifida after birth.

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