Chiari malformations (CM) occur when brain tissue extends into the upper spinal canal.

The condition is most commonly caused by congenital (present at birth) malformations in the region of the skull where the brain and spinal cord meet.

Type I Chiari malformations are thought to impact approximately 1 in 1,000 births in the United States. Some cases do not cause symptoms, so the actual number may be higher.

Doctor points to the foramen magnum of the skullShare on Pinterest
The foramen magnum (pictured) is a small opening in the skull where the brain connects to the spinal cord. If the skull is misshapen then a part of the cerebellum may move through the foramen magnum.

Normally, the skull holds the brain stem and cerebellum, the part of the brain responsible for movement coordination and muscle tone. The spinal cord connects to the brain through a small opening in the skull, called the foramen magnum.

When the skull is underdeveloped or misshapen, or a severe amount of spinal fluid is lost, parts of the cerebellum may travel downward through this small opening.

If the cerebellum protrudes into the spinal canal, it can become constricted. Depending on the intensity of the pressure, problems with brain function may occur.

Circulation of the cerebrospinal fluid circulation (CSF) may also become difficult. Cerebrospinal fluid cushions the brain and spinal cord from damage. The fluid is also responsible for circulating nutrients and removing waste from the brain.

A syrinx, or fluid-filled cyst, may also form in the spinal cord, worsening the pressure.

The majority of Chiari malformations are primary or congenital cases. They are caused by physical defects in the structure of the brain, skull, and spinal column that occur during fetal development.

Conditions associated with Chiari malformations include:

  • myelomeningocele, a form of spina bifida
  • under-developed posterior fossa
  • scoliosis
  • fluid-filled cysts in the spinal cord
  • malformed or thickened occipital bone
  • Ehlers-Danos syndrome, a connective tissue condition
  • over-crowding of the brain and spinal tissues

Most people who seek medical attention for Chiari malformations are between the ages of 20 and 40. Chiari formations are three times more common in females than males.

Recent studies indicate that there may be a genetic association with Chiari malformations.

In rare cases, severe trauma, disease, infection, or surgery can lead to the loss of large amounts of spinal fluid, causing secondary Chiari malformations.

Whether primary or secondary, Chiari malformations are further classified into three different types based on the brain regions involved and the severity of the case.

The types of Chiari malformations and their most common symptoms include:

Chiari malformation type I

Type I malformations are considered the most common type of Chiari malformation. They occur when the two lower, round lobes of the cerebellum push through the foramen magnum. These lobes are called the cerebellar tonsils.

Type I malformations usually do not have any obvious symptoms. However, potential symptoms can include:

Type I malformations may go undiagnosed because the symptoms are not always present or severe, or may be associated with other conditions.

The condition is often only identified during tests for other conditions.

Chiari malformation type II

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Multiple rounds of surgery may be required to help manage Chiari malformations.