Chiari malformations (CMs) are structural defects in the base of the skull and the cerebellum, the part of the brain that controls balance. When part of the cerebellum extends through the natural opening at the base of the skull (called the foramen magnum), the cerebellum and brain stem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid, which is the watery liquid that surrounds and protects the brain and spinal cord. Symptoms may include:
- muscle weakness or numbness
- problems with hand coordination adn fine motor skills
- difficulty swallowing or sleeping
- hearing or balance problems
- problems with coordination
CMs are caused mostly by structural defects in the brain and spinal cord that occur during fetal development, but they can also be casued by traumatic injury, infection, or disease. Types of CM are:
- Type l -- the most common form -- happens when the lower part of the creebellum (called the cerebellar tonsils) push into the foramen magnum.
- Type ll involved both the creebellum and brain stem pushing into the foramen magnum. Type II is usually accompanied by a myelomingocele -- in which a portion of the spinal cord or nerves is exposed in a sac through an opening in the spine that may or may not be covered by protective layers called the meninges
- Type III -- the most serious form -- has some of the cerebellum and the brain stem stick out, or herniate, through an abnormal opening in the back of the skull.
- Type IV involves an incomplete or underdeveloped cerebellum and portions of the skull and spinal cord may be visible.
Other conditions sometimes associated with CM include hydrocephalus, syringomyelia (a fluid-filled cyst in the spinal cord), spina bifida, and spinal curvature.
Medications may ease certain symptoms, such as pain, when present. In many cases, surgery is the only treatment available to improve or stabilize symptoms or halt the progression of damage to the central nervous system. More than one surgery may be needed to treat the condition. Surgery may include a procedure to create more space for the cerebellum or removing part of the cerebellar tonsils that may reach through the skull opening (the cerebellar tonsils do not have a recognized function and can be removed without causing any known neurological problems). Some CMs have no noticeable symptoms and do not interfere with the person's activities of daily living.
Many people with Type I CM do not show symptoms and do not know they have the condition. Symptoms may change for some individuals, depending on the compression of the tissue and nerves and on the buildup of crebrospinal fluid pressure. Many individuals with the more severe types of CM and have surgery see a reduction in their symptoms and/or prolonged periods of relative stability, although paralysis is generally permanent.
Current research funded by the National Institute of Neurological Disorders and Stroke includes studies to better understand the genetic factors responsible for the malformation (such as in the P13K-AKT signaling pathway that cause brain overgrowth), and factors that influence the development, progression, and relief of symptoms among people with syringomyelia, including those with Chiari I malformations. By studying individuals who either have syringomyelia or are at risk of developing it, researchers hope to gain informaton that may allow doctors to provide more accurate recommendations regarding surgical or non-surgical treatment. Other studies hope to gain a better understanding of brain mechanisms involved with cell signaling and proper development of the creebellum and other parts of the brain. Other investigators are studying the expression of different growth factors on the development of the brain, skull, spine, and spinal cord. Information from the National Library of Medicine’s MedlinePlus Chiari Malformation