Chiari malformation

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at November 1, 2016
StartDiseasesChiari malformation

Chiari malformation (CM) occurs when the skull is misshapen or part of the skull is smaller than normal. This places downward pressure forcing the brainstem and cerebellum into the spinal canal. In the past it was thought to be uncommon, but imaging tests made possible by advanced technology have allowed doctors to make better diagnoses, and scientists have discovered that CM is more common than previously thought. However, it is difficult to make an accurate estimate as to how often it occurs because some children born with CM never develop the symptoms.


Definition & Facts

A person has a Chiari malformation when there is not enough space for the cerebellum, the part of the brain that controls a person’s balance and muscle movement. The cramped quarters caused by an underdeveloped skull push the cerebellum down into a space that normally only holds the spinal cord. There are four main types of CM that are classified per the severity of the condition, and they are:

  • Type I is the most common type, and the only type that can be acquired. It occurs when the cerebellar tonsils extend into the hole in the base of the skull.
  • Type II is when both brainstem [[tissue] and the cerebellar extend into the hole at the base of the skull. Also, the nerve tissues that connect the two halves of the cerebellum are usually partially or completely absent. It is generally accompanied by a defect of the spine and spinal cord. Type II is seen at birth.
  • Type III is the most serious type of CM. It occurs when the cerebellum protrudes or herniates through the hole at the base the skull. It is also a rare type that causes neurological defects.
  • Type IV is when the cerebellum is undeveloped or incomplete. In some cases, parts of the spinal cord and skull are exposed. This type is rare.

Symptoms & Complaints

There are many different types of symptoms and complaints that stem from Chiari malfunctions. In addition, symptoms can change depending on the buildup of the resulting pressure. With Type I CM, children may not experience any symptoms initially, but later in life, they can start to have some difficulties. If the malformation is severe, the person may experience:

Infants born with CM, may have symptoms such as:


Chiari malformations stem from several different causes. The primary cause is improper development of the skull during the time of fetal growth. These defects are known as congenital or primary CM and may be caused by malnutrition or genetic mutations. Secondary CM is much less common and occurs when spinal fluids from the lumbar or thoracic areas are drained excessively. This can happen later in life due to an injury, infection or exposure to harmful chemicals.

Diagnosis & Tests

Because Type I CM is the most common and many people have no symptoms, the condition is usually discovered by accident while diagnosing another health issue. When the condition is discovered, the doctor will check on the functions controlled by the cerebellum, which are balance, fine motor skills, memory, sensation and reflexes. Doctors may use X-rays and CT scans to help with the diagnosis, but magnetic resonance imaging (MRI) is considered the most accurate way to diagnose CM. MRIs produce a detailed image of the parts inside the body, such as tissues, bones, organs, and nerves. Two other important tests that may be performed are:

  • Somatosensory evoked potential (SSEP) is a test that determines if messages from the brain travel properly through the spinal cord.
  • Brainstem auditory evoked response (BAER) measures the response of the brain to sound to determine if the brain is working properly.

Some birth defects such as spina bifida can cause CM, so children born with these defects are tested for CM.

Treatment & Therapy

In many cases, CM does not seriously interfere with a person’s ability to live a normal life. Doctors may prescribe medication to reduce pain and deal with other symptoms. In some children, CM is associated with behavioral and learning problems, but doctors are not sure whether these problems are caused by the CM or just a reaction to the symptoms.

However, when CM interferes with normal functions, the only treatment available to correct disorders and stop the damage being caused to the central nervous system is surgery. The aim of a surgical procedure is to:

  • Reduce pressure on the brain and spinal cord
  • Re-establish proper fluid circulation in and around the area

After surgery, most will experience extended periods of comparative stability, but the person may require more than one surgery to treat the condition. The success of the surgery depends on the severity of the symptoms that existed before surgery. For some people, surgery provides no relief of symptoms and there is a risk of serious complications. It is important to discuss surgical options with the doctor as treatment is tailored to the person.

Prevention & Prophylaxis

The cause of a Chiari malformation is that the skull is too small for the brain, and the reason a small skull forms is not known; therefore, doctors have not yet discovered a way to prevent the malformation from happening. At present, no test can be done during pregnancy to discover if the baby will be born with CM. Most children with CM do not experience any problems, and those that do, can find relief with medication and live normal lives.

CM can run in families, and it is thought that children born with CM have inherited a faulty gene that causes the skull to not develop properly. However, the risk of passing the gene on to the next generation is small, and even if they inherit it, they may never develop the symptoms. Later in life, Type I malformations can develop in people who have some types of tumors, extra fluid in the brain, and a tethered spinal cord.