Chiari 1 Malformation

Chiari 1 malformation is the least serious form of Chiari malformation, a (usually) congenital neurological disorder discovered by Austrian pathologist Hans Chiari in the 1890s. The disease occurs when part of the skull is misshapen or abnormally small, causing the lower parts of the brain, or cerebellum, to be pushed downwards so that they are below the entrance to the skull. It is sometimes known as Arnold Chiari 1 malformation, although this term has also been used to refer to type 2 of the condition.

Types 2, 3 and 4 Chiari malformation are more serious and are associated with spina bifida, neurological deficits, and, in the case of type 4, infant death, but these types are also less common. Most people with the disease will have Chiari malformation type 1, where the cerebellar tonsils at the lowest part of the back of the brain are too large to be contained within the skull, and so drop down into the top of the spinal canal. This can block the flow of cerebrospinal fluid (CSF), which carries nutrients to the brain, removes waste and protects the brain and spine. It can also create pressure at the base of the brain.

Causes and Risks of Developing Arnold Chiari

Although Chiari 1 malformation is rare, the lack of symptoms in many type 1 patients makes it difficult to estimate the number of people affected. It was once thought that this was around 1 in 1,000, but due to improvements in imaging tests in recent years, it is now believed to be higher.

Usually, Chiari malformations are caused by the failure of the brain and spinal cord to develop properly in unborn babies, something in which a lack of proper nutrients in the mother's diet can be a factor. It is also possible that there is a genetic link, as the condition has been known to run in families, although research in this area is still ongoing. The risk of a child inheriting the disease from a parent, however, is low, and most of those who do will never go on to develop symptoms.

In rare cases, injury, infection or exposure to harmful substances can cause excessive draining of cerebrospinal fluid and thus development of Chiari 1 malformation.


Many people with this neurological disorder will never develop symptoms, while some will only do so in later life. Those who do may experience the following:


In many people, symptoms of Chiari 1 malformation remain mild. In others, however, they can be severe and degenerative, leading to complications such as the following:

Diagnosis and Treatment

Often, people with Chiari 1 malformations have no symptoms and the condition may be discovered by chance during an MRI scan (magnetic resonance imaging brain scan) performed to investigate an unrelated problem. Those complaining of the symptoms listed above will be given a neurological examination, in which memory, balance, reflexes and motor skills will all be tested. Finally, an MRI scan will probably take place to confirm a Chiari malformation. Thorough examination is important as many symptoms can be associated with other conditions such as migraines or multiple sclerosis.

Chiari 1 malformation treatment will depend on the severity of the symptoms. Head and neck pain, for example, can often be managed with painkillers. However, in the case of a patient also suffering from complications such as syringomyelia or hydrocephalus, a doctor may decide that decompressive surgery is necessary. This can be done in one of the following ways:

Children with tethered cord syndrome may need an operation known as untethering, to detach the spinal cord from the bone and release pressure on the spine.

As with all surgery, these procedures are not without risks. There is a small chance that surgical Chiari malformation treatment may fail to improve or even worsen symptoms, while other risks include haemorrhage, paralysis of arms and legs and memory loss. However, in the majority of cases, surgery both improves the existing symptoms of Chiari 1 malformation and prevents further degeneration.