Chiari Malformation: Explaining A Complex Neurological Condition

What is Chiari Malformation?

Neurological Conditions

Chiari Malformation is a malformation of the back, bottom portion of the skull that results in herniation of the cerebellum. The bottom of the skull is formed too small, leaving little room for the cerebellum to fit comfortably. This results in a portion of the cerebellum herniating downward into the spinal canal. This herniated brain matter, referred to as the “cerebellar tonsils,” can lead to several serious medical problems. It can create pressure on the brainstem, resulting in impaired autonomic functions or sleep apnea. It can also block cerebrospinal fluid from flowing freely throughout the spinal canal, resulting in an accumulation of fluid in the spinal cord called a syrinx or an accumulation of cerebrospinal fluid in the brain called hydrocephalus.


Many people who have Chiari have no idea that they have the condition until symptoms arise. In most cases Chiari is congenital, meaning it is present at birth, but there have been recorded cases of acquired Chiari from traumatic events such as car accidents.


Neuro Conditions

Types of Chiari Malformation

Chiari Malformation occurs in five different manifestations that vary in severity. While you do not progress from one type of Chiari to the next, the types do increase in severity and have increasingly worst prognoses.

Chiari 1

This is the most common type of Chiari Malformation. This is when the lower part of the cerebellum, the cerebellar tonsils, extend downward into the spinal canal. Older medical literature stated that cerebellar tonsils extending at least 5mm past the foramen magnum were considered Chiari. Recent studies have shown that even patients whose cerebellar tonsils extend less than 5mm into the foramen magnum can have severe symptoms.

Chiari 1.5

This type of Chiari has only recently been recognized as a manifestation of the condition. Chiari 1.5 refers to the herniation of both the cerebellar tonsils and the brainstem downward into the spinal canal. This can result in serious medical complications, such as increased likelihood of brainstem compression.

Chiari 2

Chiari 2 is a much more serious type of Chiari than the previous two types. It is apparent early in infancy and can lead to life-threatening complications. Chiari 2 refers to the downward displacement of the cerebellum, brainstem as well as the presence of a myelomeningocele. A myelomeningocele is a form of spinal bifida that occurs when the spinal canal and backbone fail to close before birth.

Chiari 3

Chiari 3 is a very rare and very serious type of Chiari malformation. It occurs when the cerebellum and brainstem actually protrude out of an abnormal opening in the back of the skull. Babies born with this type of Chiari usually suffer life-threatening complications and ultimately have a very poor prognosis.

Chiari 4

Chiari 4 is the rarest form of Chiari and refers to the incomplete development of the cerebellum. In this type of Chiari, entire parts of the cerebellum do not develop and portions of the spinal cord may be visible outside the spinal column.

Chiari Brain


Since Chiari Malformation can lead to brainstem compression or the blockage of cerebrospinal fluid, it can lead to a multitude of wide-ranging symptoms including, but not limited to the following:

  • Headaches
  • Dizziness
  • Fainting
  • Head Pressure
  • Heart Palpitations/Tachycardia
  • Ringing in the Ears
  • Difficulty Swallowing
  • Difficulty Breathing/Shortness of Breath
  • Nausea
  • Vomiting
  • Numbness and Tingling in Extremities
  • Weakness in Extremities
  • Sleep Disturbances/Sleep Apnea
  • Visual Disturbances and Blurry Vision
  • Incontinence
  • Difficulty With Fine Motor Skills
  • Neck Pain
  • Back Pain
  • Pain in the Extremities
  • Loss of Coordination
  • Memory Issues
  • Seizures


Brain MRI

A Chiari Malformation is seen on MRI imaging. The yellow arrow indicates the herniated portion of cerebellum, the cerebellar tonsils. The yellow line indicates the foramen magnum, the area that the cerebellum does not extend past in normal imaging.

In some instances Chiari Malformation can be diagnosed through a CT scan of the brain. However, the preferred method is an MRI of the brain. An MRI provides a more detailed picture of the Chiari Malformation. With the diagnosis of Chiari Malformation, it is recommended to have a full spinal MRI to check the spinal cord for syrinx formation.

For many patients it takes years, or even decades, to diagnose Chiari Malformation. Since the condition presents such wide-ranging symptoms, many other conditions are suspected prior to Chiari. If you suspect you have Chiari Malformation, you may want to request a CT scan or MRI of the brain.


Chiari Treatment

Decompression surgery for Chiari Malformation removes the back, bottom portion of the skull as well as the back of the C1 and C2 vertebrae if necessary.

If a Chiari Malformation is discovered inadvertently and the patient is not experiencing symptoms, a “wait and see” approach is usually taken. Once a patient has become symptomatic, the only treatment for Chiari Malformation is brain surgery. The surgery is essentially to “decompress” the herniated brain matter and resolve any brainstem compression or cerebrospinal fluid blockage. Decompression surgery consists of removing a small portion of bone at the bottom of the skull, giving more room for the cerebellum to sit comfortably. If the cerebellar tonsils extend further down into the spinal column, the back of the C1 and C2 vertebrae may be removed as well. Many surgeons will also expand the dura, the outer casing of the brain, using a dural patch made from the patient’s own muscular tissue. In some cases, the herniated portion of the cerebellum needs to be cauterized or resected to create more room for spinal fluid flow. It is important to note that since Chiari Malformation is a structural deformity rather than disease, it cannot be cured. Surgery is only used to alleviate symptoms and decrease the likelihood of progressing symptoms.

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