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Small posterior fossa, EDS, related issues

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Ehlers-Danlos, CSF and MS

Ehlers-Danlos Syndrome is one of many different types of inherited and acquired disorders, as well as degenerative conditions (aging and wear and tear) of the craniocervical junction (skull and upper cervical spine junction) that can cause an array of neurological signs and symptoms such as dysautonomia and multiple sclerosis (MS). I address them together in my book and call them craniocervical syndromes.

Craniocervical syndromes can affect CSF and blood flow going into and out of the brain. They can also cause compressive myelopathies of the cervicomedullary cord. In other words, they can cause the lower brainstem and upper spinal cord to malfunction due to compression.

Ehlers-Danlos Syndrome is a hereditary disorder of connective tissues far too complex to elaborate upon on this page. It is important to note that you have to inherit the condition, which means you can't get it from multiple sclerosis. You have to be born with it. On the other hand if you have the condition it makes you highly susceptible to getting multiple sclerosis. In brief, it is an inherited connective tissue disorder associated with loose tissues that can cause numerous problems such as overly flexible joints (hypermobile), skin that overstretches, dilated blood vessels and organs, as well as scoliosis of the spine to name a few.

As far as this page is concerned, Ehlers-Danlos syndrome often affects the design and function of the skull and spine. Moreover, while most cases are not affected there is a significant incidence of multiple sclerosis (MS) in patients with Ehlers-Danlos Syndrome (EDS) due to their increase in susceptibility caused by structural problems in the skull and upper cervical spine.

In fact, the connection of EDS to MS underscores the role of upper cervical subluxations, Chiari malformations and cerebrospinal fluid flow (CSF) in neurodegenerative diseases such as multiple sclerosis (MS).

Chiari malformation

As far as design of the skull is concerned, Ehlers-Danlos syndrome is sometimes associated with underdevelopment, called hypoplasia, of the different parts of the skull including the posterior fossa of the base. The posterior fossa contains the cerebellum and brainstem. The cerebellum is a cauliflower shaped structure in the back of the skull at the bottom of the brain.

The front side of the posterior fossa is formed by the clivus, which is the slanted floor of the base of the skull in front of the belly (ventral) side of the brainstem. The backside is formed by the bowl of the occipital bone which contains the cerebellum. The cerebellar part of the posterior fossa is covered by a tent-like connective tissue membrane called the tentorium cerebelli. The tent is not flat. It sits at an angle. It's open on the front side like a pup tent. The opening accommodates the brainstem.

In the brain scan above, the brain and bones of the skull and spine are gray and cerebrospinal fluid is white. The arrow in this image points toward the tonsils of the cerebellum. Underneath the arrow is a gray area, which is the backside of the foramen magnum called the opisthion. Across from the arrow, in front of the brainstem (the gray tube surrounded by white channels, CSF) is a triangular looking shaped bone (light grey).

Above it is the part of the sphenoid bone shaped like a cup which holds the pituitary gland. The backside of the cup and triangular bone is called the clivus portion of the base of the skull. The foramen magnum lies between the bottom point of the clivus and the opisthion, mentioned above, and just below the cerebellum. The white line on top of the cerebellum (cauliflower looking structure) is the tentorium cerebelli mentioned above.

Hypoplasia, in this case shortening, of the occipital portion of the posterior fossa in Ehlers-Danlos causes crowding of the cerebellum. In some cases it causes a significant increase in the pitch of the tentorium cerebelli over the posterior fossa. A short base also forces the cerebellum forward and downward toward the foramen magnum. In addition, the decrease in space tends to squeeze CSF out of the brain.

Thus, hypoplasia of the posterior fossa predisposes certain EDS patients to Chiari malformations in which the cerebellum gets squeezed into the foramen-magnum or comes in contact with the base of the skull. Typically it is the tonsils of the cerebellum that are affected.

Furthermore, some Ehlers-Danlos patients have a short clivus. The clivus is the slanted part of the base of the skull mentioned above. It is the front side of the posterior fossa. The front of the belly side of the brainstem lies behind it. A short clivus tends to indicate a lower ceiling height in the posterior fossa which further crowds the cerebellum and brainstem. In addition, the short clivus predisposes certain cases of EDS to Chiari malformations that put pressure on the belly side of the brainstem in front of the foramen magnum, which likewise can affect CSF flow.

To further complicate matters, as a result of increased elasticity of connective tissues, as mentioned above, Ehlers-Danlos patients often have hypermobile joints, including the joints of the spine. The hypermobility of joints can cause subluxations and dislocations in the hands, feet, elbows and shoulders, as well as scoliosis and kyphosis in the spine. Hypermobility of the cervical spine can cause chronic subluxations of the upper cervical spine. Chronic subluxations of the upper cervical spine can sometimes cause a pannus formation on the odontoid process of the second cervical vertebra (C2), also known as axis.

In the picture on the right the odontoid process portion of the axis vertebra is the tooth-like projection, that points cranially (toward the head). It rests in a pocket in the atlas vertebra (C1) above it seen in the picture below. It serves as a pivot joint. Most of the rotation in the neck takes place around the odontoid process.

During foward and backward head and neck movement, the odontoid process is generally held in proper position in the atlas vertebra by the transverse ligament. The transverse ligament can be seen in the picture at the posterior aspect of the odontoid attaching from one side of the inner ring of atlas to the other, holding the odontoid in place.

Hypermobility in Ehlers-Danlos, decreases the ability of the transverse ligament to hold the odontoid in place. This causes excess motion between the odontoid process in the pocket of the atlas vertebra causing chronic irritation and swelling. This chronic irritation can cause a cyst, called a pannus in this particular case, to form on the odontoid process of axis. The pannus cyst formation invades and, consequently, compresses the contents of the spinal canal. In addition to EDS, pannus formations are also seen in other conditions such as rheumatoid arthritis.

The arrow in the brain scan points to a pannus formation (ring like structure) over the odontoid process of axis causing it to compress and indent the spinal canal. Among other things, the upper cervical spinal canal contains the subarachnoid space for the flow of CSF between the brain and cord. Compression of the contents of the spinal canal can thus affect CSF flow going into and out of the cranial vault.

While Chiari malformations have been reported in some EDS cases, I suspect that other cases may be associated with benign intracranial hypertension (BIH) and still others with normal pressure hydrocephalus (NPH). In any case, EDS patients often get MS signs and symptoms and the problem stems from poor CSF flow.

By studying and trying to solve problems with CSF flow seen in Ehlers-Danlos cases we can learn more about the role the design of the skull and upper cervical spine play in Chiari malformations and CSF flow in other neurodegenerative conditions that affect the brain and cord such as Alzheimer's disease, Parkinson's disease and multiple sclerosis. Humans are predisposed to problems with blood and CSF flow in the brain and cord due to changes in structure as a result of upright posture. Ehlers-Danlos or EDS is just one of many conditions.
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