Chiari Malformation

This post is about Chiari Malformation; there are many articles, forums, and blogs about people suffering from Chiari Malformation that finally are correctly diagnosed after a lifetime of misdiagnoses or being told it is “all in their head”-little did they know that was all too true. For a large list of symptoms, see http://chiarione.org/symptoms.html. My example is from http://ihavechiaritype1.blogspot.com/ by a person named Jenn Ann. I am linking this condition to Chapter 2 in our textbook. Chiari Malformation is a disease first recognized in 1890s by Professor Hans Chiari. Chiari Malformation is a congenital defect involving hypoplasia of the posterior fossa and the descent of the cerebellar tonsils through the foramen magnum. This neurological condition can cause a wide array of symptoms that have the potential to drastically alter a person’s life.

The cerebellum is a part of the brain that sits in the back and at base of the skull. It is often referred to as a “little brain” because of its shape and its striated appearance mimics the gyre of the cerebral hemispheres. Maintaining balance and coordination of voluntary motor control are key functions of the cerebellum. The cerebellum also plays a role in muscle tone; someone with damage to the cerebellum may have slurred speech, abnormal eye movements, and weakness of limb muscles as well and would tend to be asymmetric in the degree of weakness.

People presenting with Chiari can be evaluated with a neurological exam that, among other factors, tests for improper reflexes, such as a Babinski, an asymmetric gag reflex, and an asymmetric pupil response to light. Maintenance of a normal gait is a function of the cerebellum, and as a result damage to it can result in a very wide gait to protect from falling. The position of the cerebellum causes it to respond to pressure in different ways than the rest of the brain. It is located above the foramen magnum (the hole in the base of the skull allowing entrance of the spinal cord). The medulla and pons also make up the majority of the brain stem, an important autoregulating structure of the brain. They share several of their functions and complement each other where they differ. They moderate heart rate, respiratory rate, blood pressure, and vasodilation/constriction as well as serving as a link to the cerebellum. Displacement of the cerebellar tonsils, usually as a result of dysplasia, anteriorly and inferiorly through the foramen magnum creates pressure. The cerebellum directly pushes on the medulla and pons causing many heart rate, blood pressure, and autoregulatory abnormalities to potentially develop. The wedging of the cerebellar tonsils between the brainstem and the wall of the foramen magnum can significantly reduce the size of the canal. 


Some patients with no herniation of the tonsils can experience symptoms just as severe as patients who have five or greater millimeters of herniation. One explanation for this could be the descent of the tonsils, as seen on an MRI, just takes two dimensions into account (from a sagittal view). The total space they occupy in relation to the size of the canal/degree of hypoplasia of the posterior fossa is not taken into account. The narrowing of the canal restricts CSF flow. Because cerebrospinal fluid flows in a pulsing manner, if CSF flow is blocked or restricted at the base of the skull, pressure (intracranial pressure) will increase dramatically. If outflow is hindered, ICP can increase with each pulse. Build up of CSF can result in several dangerous or crippling conditions, such as Hydrocephalus and Syringomyelia. I won’t go into the details of those conditions or discuss cerebral perfusion pressure, as I’ve already written too much. Needless to say, this is a highly variable disease that is potentially debilitating but also can manifest completely asymptomatically.