Chiari malformation

What is a chiari malformation?

A chiari malformation is an abnormality in the structure of the brain, in which the lower parts of the brain push downwards into the spinal canal. This can block the flow of cerebrospinal fluid (CSF) and create pressure in the brain. There are different types of chiari malformations: 

  • Type I - this is where parts of the cerebellum extend down into the spinal canal. It is the most common type of malformation. People with a Type I malformation may not experience any symptoms; it is therefore sometimes only detected by chance when a CT or MRI scan is performed for an unrelated concern. Type I malformations are not considered to be life-threatening. They can often lead to a condition called syringomyelia, in which CSF builds up in the spinal canal and puts pressure on the spinal cord. 

  • Type II - this is where both the cerebellum and the brainstem extend downwards out of the base of the skull and press against the spinal canal. It often causes a range of symptoms and is more serious than Type I. It is sometimes known as Arnold-Chiari malformation. This type of malformation is often associated with spina bifida, a condition in which the spine does not develop properly.

  • Types III and IV - these are the most serious forms of malformation, and they cause severe neurological problems. Both types are rare. Symptoms for Types III and IV often appear early on in life during birth and infancy. 

Causes of chiari malformations

Chiari malformations are caused by structural abnormalities in the brain or parts of the skull not being large enough for the brain. It is not exactly known what causes these abnormalities to form in the first instance. They can sometimes be the result of problems during prenatal development, such as genetics, abnormal fetal development and improper nutrients in the mother's diet. They are often associated with other conditions such as hydrocephalus and spina bifida. An infection or injury to the brain or spine can also cause a chiari malformation. 

Diagnosis and treatment of chiari malformations

Chiari malformations are often diagnosed when a CT or MRI scan is performed and the characteristic abnormalities of the lower parts of the brain are detected. A person may go in for a scan because of their symptoms, or for unrelated reasons if they do not have any symptoms, in which case the malformation may only be detected by chance. A neurological examination may also be carried out to diagnose a chiari malformation. 

Symptoms of chiari malformations can be managed with medication. Treatment often involves surgery. A form of surgery called decompression surgery is often used to create more space for the brain. This is where a small piece of bone is removed from the base of the skull to reduce pressure on the brain and enable CSF to flow normally. An endoscopy third ventriculostomy (ETV) may be used to drill a small hole in the brain to release extra CSF and reduce pressure. In some instances, a shunt may be inserted to drain away excess CSF. It may be necessary for a person to undergo several surgical procedures to treat a chiari malformation. 

Effects of chiari malformations

For information on the effects of chiari malformations, visit the effects of brain injury section.