"When symptoms such as headaches, dizziness, and fatigue persist, they often rob a person of their quality of life. Though not everyone experiencing these symptoms is suffering from Chiari I Malformation, for those that are, we're here to provide answers and options." - John Oró, M.D.
ANATOMY
The brain is enclosed in the skull, which is a rigid bone. There are 2 main compartments, or hemispheres. The upper compartment, which contains the hemispheres, and a lower compartment called the posterior fossa. Within the hemispheres are fluid-filled cavities called ventricles. The fourth ventricle is between the brainstem in the lower compartment. The ventricles are pockets filled with cerebrospinal fluid (CSF), which flows around the brain and spinal cord. The CSF is a clear, water-like substance produced in the lateral ventricles. The total CSF volume is approximately 150 ml (or about a pint). It is normally absorbed and reproduced about 4 times per day in the adult. Cerebrospinal fluid normally flows through the ventricles, down through the posterior fossa (back area of the brain) and into the spinal canal. The function of the cerebrospinal fluid is to bathe and nourish the brain and spinal cord.
The lower-most part of the brain is the cerebellum and brain stem, which are located in an area called the posterior fossa. This is the area just at the base of the skull, which attaches to the spinal cord. Within the posterior fossa lies the brainstem and cerebellum. The fourth ventricle is also located within the posterior fossa. The cerebellum is the lowest part of the brain. The cerebellum is made up of three major lobes, which are composed of nerve fibers connecting to the brain stem. There are two small portions of cerebellar tissue, the cerebellar tonsils, which normally lie within the posterior fossa. These tonsils are different from those located in the throat. The function of the cerebellum is thought to maintain coordination and fluidity of movements. Gait, balance, posture and coordinated movements are thought to be controlled in the cerebellum.
CHIARI I MALFORMATION
The Chiari malformation (CM) was first identified in 1891 by Dr. Chiari. It is an uncommon, complex, neurologic deformity which is present at birth.The brainstem normally sits in a funnel-like cavity just above the spinal cord. The problem occurs when the posterior fossa is not formed properly. Instead of the brainstem sitting in its proper space, the cerebellar tonsils are displaced downward into the funnel, thus causing pressure on this part of the brain and spinal cord (Figure-1).
There can also obstruction of the normal flow of CSF through this area because the tonsils of the cerebellum are “stuffed” into the funnel. Sometimes the brainstem appears atrophic (or shrunken), or elongated (stretched). This downward displacement of the cerebellar tonsils is called the Chiari malformation. Although there is a form of Chiari malformation which occurs in children with meningomyelocele, the Chiari I malformation more frequently causes problems in adults.
The exact cause of the Chiari malformation is unknown. It has been suggested that the Chiari malformation occurs during early embryo development of the brainstem and spinal cord. An abnormally small posterior fossa forces the brainstem downward. Persons with Chiari I malformation often have no symptoms until the third or fourth decade of life.The Chiari I malformation occurs more often in women than men. There is no particular ethnic or geographic incidence of this disorder. The Chiari malformation does seem to run in some families, but a specific gene has not been identified.
Some people with Chiari I malformation also have a syrinx (se-ri-nx) or syringomyelia (Figure 2).
Read about syringomyelia under related disorders section.