What is Chiari Malformation?

Chiari Malformation

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 opening at the base of the skull, the cerebellum and brain stem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid (CSF, the liquid that surrounds and protects the brain and spinal cord). Symptoms may change for some individuals depending on buildup of CSF and any resulting pressure on tissue and nerves. Other conditions sometimes associated with CM include hydrocephalus, syringomyelia (a fluid-filled cyst in the spinal cord), and spinal curvature.

What causes Chiari malformations?

  • Primary or Congenital malformations are often caused by structural defects in the brain and spinal cord that occur during fetal development. This can be the result of genetic mutations or a maternal diet that lacked certain vitamins or nutrients.
  • Acquired or Secondary Chiari malformations are caused later in life if spinal fluid is drained excessively from the lumbar or thoracic areas of the spine either due to traumatic injury, disease or infection.

What are symptoms of Chiari malformations?

  • Headache is the hallmark sign of Chiari malformation, especially after sudden coughing, sneezing or straining. Other symptoms often vary among individuals and include:
  • Neck pain
  • Hearing or balance problems
  • Muscle weakness or numbness
  • Dizziness
  • Difficulty swallowing
  • Vomiting

How are Chiari malformations classified?

CMs are classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal:

  • Chiari Malformation Type I: The most common form. Occurs when the cerebellar tonsils extend into the foramen magnum. It is usually noticed in adolescence or adulthood, often by accident during an exam for another condition.
  • Chiari Malformation Type II: This is also referred to as classic Chiari malformation, where the cerebellum and brain stem tissue protrude into the foramen magnum. The nerve tissue that connects the two halves of the cerebellum may be missing or partially formed. Type II is usually accompanied by a myelomenigocele-a form of spina bifida that occurs when the spinal cancal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening.
  • Chiari Malformation Type III: Very rare and the most serious form of Chiari malformation. In this type, some of the cerebellum and the brain herniate through an abnormal opening in the back of the skull. Symptoms include those seen in Type II, in addition to sever neurological defects.
  • Chiari Malformation Type IV: Involves an incomplete or underdeveloped cerebellum. In this rare form of Chiari malformation, the cerebellum is loated in its normal position but parts of it are missing and portions of the skull and spinal cord may be visible.


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.

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