Chiari malformations are typically associated with herniation of the brainstem into the foramen magnum in the base of the skull as shown in the picture on the left. More recently, it has come to include what is called a Zero Chiari Malformation in which the cerebellum comes in contact with the base of the cranial vault without herniation into the foramen magnum. This has prompted some researchers to suggest that Chiari malformations include any decrease in cerebrospinal fluid volume (CSF) sufficient enough to cause the brain to sink and come in contact with the bones of the base of the skull.
Considering the above, in addition to the foramen magnum there are other large holes in the base of the skull through which cranial nerves and blood vessels pass, as seen in the picture on the right. It is possible that the cranial nerves may herniate into the openings or come in contact with the base of the skull due to Chiari malformations in which the volume of CSF falls too low, as mentioned above. The consequence would be similar, as well, that is cause compression of nerves and circulatory routes.
The brain floats within the cranial vault. Typically, it is prevented from sinking into the foramen magnum by the cisterns of the brain which are filled with cerebrospinal fluid (CSF). The cisterns are also strategically placed to provide cushioning, support and protection from the hard bones of the cranial vault as seen in the picture on the left.
Symptoms of MS often include cranial nerves. Common complaints include dizziness, ringing in the ears or loss of hearing, trigeminal neuralgia, burning tongue and dry mouth. By far, however, the cranial nerve most commonly involved in MS is the optic nerve. Optic neuritis is, in fact, one of the most frequent symptoms of MS. Even Asians and African-Americans who, otherwise, have a much lower incidence of MS, get optic neuritis. They also get transverse myelitis, but that’s another topic entirely. I will be covering the different cranial nerve signs, as well as transverse myelitis on my new website starting with the optic nerve.
The optic nerve is the second most superior (highest) nerve in the cranial vault. The highest cranial nerve is the olfactory nerve to the nose which is located in the anterior fossa or forehead area of the base of the skull. The optic nerve lies in the middle fossa behind the eye sockets. Most of the cranial nerves are in the posterior fossa along with the brainstem and cerebellum.
It’s position in the cranial vault and the optic canal may be the reason why optic neuritis is one of the most common signs and symptoms of MS, optic-spinal MS and Devic’s disease. Typically, the optic nerve is protected by the chiasmatic cistern, which is one of the highest cisterns in the brain. Among other things trauma and failure of the CSF support system of the brain may play a role in optic neuritis. For further information on optic neuritis click on the link below to my new website. The website can also be found in the links section of the sidebar under upright-health.