The cerebellum is often affected in neurodegenerative diseases such as Alzheimer’s,, Parkinson’s and multiple sclerosis (MS). Cerebellar signs include: problems with posture, balance, gait (walking) and coordination. Muscle coordination problems include disturbances in movements of the eyes such as nystagmus, as well as intention tremors and over shooting movements when attempting to do specific tasks with the arms or legs. Cerebellar signs can also include problems with speech, vertigo, nausea and vomiting. In this regard the cerebellum is often affected in different neurodegenerative diseases due its location in the posterior fossa above the foramen magnum.
The brain floats inside a jacket of water. The jacket of water includes the enlarged spaces, called cisterns (wells) beneath the bottom of the brain and surrounding the brainstem and cerebellum. The cisterns are the blue spaces in the drawing above from a neurology lecture by Dr. Anne Olsen. The cisterns support the brain and protect and cushion it from the hard walls of the cranial vault.
The cisterna magna is the largest of the cisterns and is located inferior to (below the bottom of) the cerebellum. The volume of cerebrospinal fluid (CSF) in the cisterna magna and other cisterns is crititcal to the health and function of the brainstem and cerebellum. An increase or a decrease in the normal volume of CSF in the cisterns can cause problems in the brainstem and cerebellum. For example, an insufficient volume of CSF can cause the brainstem and cerebellum to sink into the foramen magnum. On the other hand, it is my opinion that a chronic abnormal increase in CSF volume in the cisterns can lead to compression and subsequent degeneration of the brainstem and cerebellum.
Typically, hydrocephalus is associated with an increase in CSF volume in the chambers in the middle of the brain and brainstem, called ventricles, where it is produced. There is debate among experts, however, as to whether to include any abnormal increase in CSF volume inside the cranial vault, which would include those that can occur outside the ventricles in the subarachnoid spaces and cisterns located between the outer and middle layers of the protective membranes, called meninges, that surround the brain and cord. Currently, an increase in CSF volume in the cisterna magna is called a mega cisterna magna or a cystic posterior fossa. At this time, a mega cisterna magna is not considered to be a form of hydrocephalus but it is sometimes associated with hydrocephalus and enlarged ventricles in a rare condition called Dandy-Walker syndrome.
Dandy-Walker syndrome is a congenital condition associated with a malformed and undersized cerebellum. The MRI on the right is an example of a Dandy Walker syndrome from a paper published in 2008 in the Internet Journal of Radiology called, Imaging of Congenital Malformations of the Brain by A.B. Shinagare and N.K. Patil from the Department of Radiology in Mumbai. The white arrow points to the cerebellum. The white dart points to the cover over the cerebellum and posterior fossa, which is exceptionally steep. The black dart near the bottom of the posterior fossa points to a dark gray area beneath the cerebellum. The dark gray is CSF in the cisterna magna of the posterior fossa. The black arrow points to the rear side of the pons portion of the brainstem, which is slightly compressed.
A normal healthy cerebellum should nearly fill the posterior fossa. In this case the cerebellum is extremely small. The malformation of the cerebellum is currently believed to be do to underdevelopment (atrophy), or to total lack of development (atresia). The increase in CSF volume in the cisterna magna is attributed to the decrease in size of the cerebellum. In other words, CSF simply moves in to fill the empy space.
Interestingly, Dandy-Walker syndrome is the complete opposite condition to a Chiari malformation. For example, Chiari malformations are often associated with an undersized posterior fossa. In Dandy-Walker, the posterior fossa is often enlarged. In Chiari malformations, a normal sized cerebellum gets pushed down into the foramen magnum. In Dandy-Walker the cerebellum is underdeveloped and small. Moreover, it often gets pushed up into the posterior fossa of the cranial vault along with the cover over the fossa, called the tentorium cerebelli. In Chiari malformations the cisterna magna is often compressed due to the descent of the cerebellum into the foramen magnum. In Dandy-Walker syndrome the cisterna magna is enlarged. Chiari malformations are also associated with an undersized foramen magnum. Dandy-Walker, on the other hand, is associated with an oversized foramen magnum. Chiari malformations also affect females about three times as often as males. On the other hand, at approximately sixty percent, males make up more than half the cases of Dandy-Walker syndrome. The one characteristic both conditions do share in common is that their cause is often unknown.
In Dandy-Walker the problem is believed to be caused by undersized or absent outlets that normally connect the fourth and lowest ventricle to the cisterns below. The fourth ventricle is located between the front of the cerebellum in the back and the pons of the brainstem in the front. It can be seen in the sketch of the cisterns at the top of the page indicated by the Roman numeral IV in the black space. The third ventricle is above it and is indicated by the Roman numeral III in the black space. The narrow black streak joing them is called the cerebral aqueduct.
The obstruction to CSF flow from the fourth ventricle to the cisterns causes the fourth ventricle to enlarge. Chronic enlargement of the fourth ventricle can compress and damage the cerebellum. In Dandy-Walker syndrome, the enlarged fourth ventricle is referred to as a cystic fourth ventricle. Because it involves the ventricles, a cystic fourth ventricle is technically a form of hydrocephalus. On the other hand, the enlarged cisterna magna seen in certain cases of Dandy-Walkers syndrome is not. Instead, the enlarged cistern is attributed to an underdevelopment resulting in an undersized cerebellum. CSF increases in volume in the cisterna magna as a result of the decrease in size of the cerebellum. Since the cisterns are outside the ventricles, technically speaking it is not hydrocephalus.
This is similar to the theory regarding the suspected cause of enlarged ventricles often seen in normal pressure hydrocephalus (NPH), which has been associated with Alzheimer’s disease, dementia and Parkinson’s disease as well as others. In Alzheimer’s disease the enlarged ventricles are attributed to atrophy; that is, a decrease in size of the brain. In other words, as the brain shrinks in size the ventricles enlarge and CSF volume increases to compensate for the decrease in size of the brain and to fill in the space.
While some cases of Dandy-Walker are clearly associated with undersized, blocked or absent CSF pathways, many are not. The problem is further complicated because the development of the ventricles, as well as the cisterns and CSF pathways start in utero (during preganancy) and continues after birth, which is when problems start to show up. Moreover, the skull is still open at birth, which allows it to accomodate an increase in CSF volume. Consequently, unless it is associated with an oversized head due to hydrocephalus, the problem often goes unnoticed initially . Whatever the cause, experts all agree that Dandy-Walker syndrome is associated with an imbalance between the rate of production of CSF and its absorption and removal from the brain.
Considering the above, both blood and CSF flow between the brain and cord pass through the foramen magnum and upper cervical spinal canal. Consequently, blockage of blood and CSF flow through the foramen magnum and upper cervical spinal canal can cause inversion flows, turbulance and standing waves to form in the brain, especially in the cisterna magna, which can affect the cerebellum among other things. It can also cause the posterior fossa and foramen magnum to enlarge similar to the affects of hydrocephalus on the upper portion of the cranial vault. This could explain the enlarged posterior fossa and foramen magnum in Dandy-Walker syndrome. Furthermore, it is my contention that chronic obstruction to CSF flow causes local turbulance, inversion flows and standing waves (clapotis) in the brain that can compress and erode the brain.
Other cisterns can similarly be affected in conditions that affect adults. For example, there is a variant of Parkinson’s disease called multi-system atropy (MSA) or olivopontocerebellar atrophy (OPCA) in which the cerebellum and sometimes parts of the brainstem, called the olives and pons, appear small and compressed similar to Dandy-Walker. It is my theory that many cases of Parkinson’s disease and variants of Parkinson’s are due to obstruction to CSF flow oftentimes due to Chiari malformations, which block blood between the brain and cord in the foramen magnum and upper cervical spinal canal. Moreover, obstruction to CSF flow most likely plays a role in multiple sclerosis and Alzheimer’s disease as well. The first place to feel the affect of blockage of CSF flow is the posterior fossa, which contains the brainstem and cerebellum.
In brief, hydrocephalus is associated with children. In contrast to children, adults get normal pressure hydrocephalus. Similarly, Chiari malformations and Dandy-Walker syndromes are associated with children. More recently however, it has been shown that adults can aquire Chiari 1 type malformations, and olivopontocerebellar atrophy (a variant of Parksinson’s) causes similar signs on brain scans to Dandy-Walker syndrome. In many cases they may share a similar cause, which is blockage of CSF flow that results in an imbalance between its rate of production and removal from the brain. Among other things, an increase in CSF volume in the fourth ventricle or cisterns can affect the cerebellum.
For further information on CSF flow and volume in the cisterns, dysautonomia and heat intolerance, visit my website at www.upright-health.com.