Sydney Brain & Spine

Chiari Malformations

Chiari Malformation is a condition in which brain tissue protrudes into the spinal canal due to astructural abnormality at the back of the brain and skull.Normally, the cerebellum sits entirely within the skull. There is a large opening in the base of the skull called the foramen magnum where the brain and spinal cord connect. The cerebrospinal fluid that protects the brain and spinal cord moves freely between the head and spine through this opening. In a chiari malformation, the cerebellum is pushed down through the foramen magnum, creating pressure on the spinal cord. This also restricts fluid movement between the brain and spine, leading to elevated pressure in the brain.

There are four types of Chiari malformations.

Type 1: Most common type of Chiari malformation. Some of the brain tissue at the base of the skull (the cerebellar tonsils) push into the skull base opening, called the foramen magnum,  where the spinal cord attaches to the brain. This commonly goes unnoticed until problems arise during adolescence or adulthood.

Type 2: Not limited to the cerebellum, also involves the brainstem and other parts of the brain.  Most of these patients will also have hydrocephalus. This is a condition in which there is an overproduction or lack of absorption of the cerebral spinal fluid (CSF) that is found inside of the ventricles (fluid-filled areas) inside of the brain. The increased fluid causes the pressure inside of the head to increase and the skull bones to expand to a larger-than-normal appearance.

Type 3:Very rare birth defect.The skull does not close completely during foetal development, causing some brain tissue to protrudeout of an opening in the back of the skull area.

Type 4:Very rare, the cerebellum does not develop normally during pregnancy



Often patients with a Type 1 Chiari malformation have no symptoms, and the malformation is identified  after undergoing an MRI for another reason.  Often patients will not experience symptoms until adolescence or adulthood. Patients that do have symptoms may experience:

  • Severe headaches, often brought on by laughing, coughing or sneezing
  • Neck pain, usually at the base of the neck and between shoulder blades
  • Gait problems
  • Loss of fine motor skills
  • Numbness and tingling of the hands and fingers
  • Dizziness
  • Difficulty swallowing, choking on fluids
  • Vision problems
  • Slurred speech


Chiari malformations can be difficult to diagnose, as the symptoms can be vague, and in some cases there may be no symptoms at all. A definitive diagnosis is generally made after a neurological examination and an MRI scan, where the abnormal protrusion of the cerebellum downwards though the foramen magnum can be seen. Anyone who receives a tentative diagnosis of a Chiari malformation should always be referred to a neurosurgeon, who will conduct an examination and recommend a course of treatment.



Some chiari malformations are asymptomatic and do not interfere with a person’s activities of daily living. In these cases treatment may not be necessary and regular monitoring by a neurosurgeon is all that is needed. In other cases, medications may ease certain symptoms, such as headaches.

Surgery may be offered to patients when medications do not ease their headache, or if they exhibit serious functional disturbances. Most patients will have a significant or complete reduction of their symptoms. The aim of chiari decompression surgery is to make more room for the cerebellum at the site of compression. This in turn relieves pressure on the spinal cord and allows the cerebrospinal fluid to move freely between the brain and spinal cord.