Cavities such as cysts and syrinxes that may or may not contain cerebrospinal fluid (CSF) are seen in the brain and cord. In this post we are concerned with the types that contain CSF. Faulty fluid mechanics in the brain and cord can cause these types of cavities to form. Likewise, cysts and syrinxes can cause faulty fluid mechanics in the brain and cord.
Cysts sometimes develop in the middle layer of the three protective coverings of the brain and cord, called meninges. If you look at the picture below, toward the bottom on the right hand side, there is a label pointing to a dark line called dura mater. The dura mater is the tough outer covering that surrounds the brain and cord. Above the dura mater is another label, called the arachnoidea, which points to a white line surrounding the brain and cord. The arachnoid mater is the middle layer of the meninges. Still another label above that points to a black line called the pia mater, which is the inner most layer of the covering of the brain and cord. The subarachnoid space is the stipled area that lies between the arachnoid and pia mater.
Arachnoid cysts are fairly common. They project out from the arachnoid mater covering and subarachnoid space. They are also called leptomeningeal cysts. Arachnoid cysts tend to occur in certain places in the brain and cord. One of the common areas is the middle fossa of the cranial vault, as well as the Sylvian fissure of the brain which is located in the middle fossa. The Sylvian fissure is a deep fold which separates the frontal, temporal and parietal lobes of the brain.
Other common areas for arachnoid cysts are, within the covering over the posterior fossa called the tentorium cerebelli (the black line over top of cerebellum), the cisterna magna (the stipled area beneath the cerebellum), which is a cistern located between the cerebellum and the medulla oblongata, and the suprasellar region, which is a cavity in a bone in the skull that houses the pituitary gland (the hypophysis hanging down beneath the front of the brain).
If you look at the middle of the brain in the picture above, the arrows start in the lateral ventricles and flow down through the third ventricle, the cerebral aqueduct, and into the fourth ventricle. They then leave the fourth ventricle and enter the stipled area which represents the subarachnoid space.
Enlarged ventricles are typically referred to as ventriculomegaly. Enlargement of the fourth ventricle, however, is sometimes classified as a cyst or cystic ventricle. A well known example of a cystic fourth ventricle is seen in Dandy-Walker syndrome which occurs in children.
Some cysts are acquired later in life, such as from trauma. Trauma can cause cysts due to tears in the meninges. It is currently maintained, however, that most people are born with arachnoid cysts. Some are caused by genetic weakness in the tissues or design flaws in the subarachnoid space. I suspect that still others may occur due to intrauterine positions of the fetus during pregnancy that can potentially increase pressure in critical areas of the brain and cord.
Some cysts are formed in the cord and are called syrinxes from the Greek word tube. If you look at the picture above you will see a canal going down through the center of the cord. The label that points to it on the left near the bottom of the canal is the canalis centralis, which means central canal of the cord. Syrinxes typically start and are found in the central canal but they can spread outwards and affect other parts of the cord.
Syrinxes are typically expansions in the central canal of the cord. The central canal is connected to the lowest ventricle in the brain, which is the fourth. These syrinxes are also referred to as syringomyelia. Similar to cysts, syrinxes are sometimes connected to and sometimes more isolated from CSF pathways, which can trap fluids.
Sometimes the cysts and syrinxes communicate with normal CSF pathways. In the case of subarachnoid cysts the fluid can flow more freely between the cyst and subarachnoid space. In other cases, the cyst is more isolated by connective tissues so that fluids that manage to find there way into the space, find it hard to get out.
Cysts and syrinxes are sometimes associated with significant pressure that causes fluids to eject forcefully when penetrated surgically. The force from the hydraulic nature of cysts and syrinxes can consequently compress nearby tissues. The turbulant flow and subsequent pounding they create can also erode nearby tissues like waves beating on rocky cliffs on a shoreline. Turbulant flow can, likewise, erode bone. In the skull it leaves impressions that look like little dents on the inside roof of the cranial vault. Researchers now suspect that the turbulant CSF flow caused by Chiari malformations may play a role in the formation of syrinxes in the central canal of the cord.
Chiari malformations obstruct CSF flow through the foramen magnum of the skull and the upper cervical spine, which can cause normal pressure hydrocephalus (NPH) in adults. Lastly, Chiari malformations and NPH have been associated with multiple sclerosis and other neurodegenerative conditions.
Cysts and syrinxes speak volumes about CSF and the hydraulic stress it causes in the brain and cord. What’s more, obstruction of CSF flow through the foramen magnum and upper cervical spine and the faulty fluid mechanics and hydraulic stresses it creates may be one of the root causes of Alzheimer’s, Parkinson’s and multiple sclerosis, as well as other neurodegenerative diseases. Ventriculomegaly (enlargement of a ventricle) has been associated with all three of these conditions. Two variants of Parkinson’s disease are also associated with cystic conditions within the ventricles and cisterns. In most cases, the cause of cysts and syrinxes is unknown.
I will be covering more on cysts and syrinxes on this blog and my website in future posts. For now, for further information click on syringomyelia above or visit my website at www.upright-health.com.