What is Chiari malformation?
Chiari malformation (CM) is a group of disorders that affect how the brain fits inside the spinal canal, the space inside the spine that contains and protects the spinal cord. In CM, the lower part of the brain that controls balance—called the cerebellum—pushes downward into the spinal canal. This can cause headaches and balance problems.
Symptoms of CM
This bulging of the cerebellum can block the flow of cerebrospinal fluid—clear liquid that surrounds and cushions the brain and spinal cord. Both the size of the cerebellum bulge and amount of leaked spinal fluid can affect how severe symptoms are.
Some people with a CM don’t have symptoms. Other people with a CM may not have symptoms at first but may develop them later in life. CM symptoms can include:
CM is associated with other neurological conditions, including:
- Hydrocephalus (buildup of spinal fluid in the brain)
- Spina bifida (bones in the back don’t completely close around the spinal cord before birth)
- Syringomyelia (a spinal fluid-filled sac in the spinal cord)
- Tethered spinal cord syndrome (tissue around the bottom of the spine holds the spinal cord too tightly)
Types of CM
People are often diagnosed with having a CM after an imaging test such as magnetic resonance imaging (MRI). There are four main types of CM, based on how much of a person’s brain pushes into the opening at the base of the skull and the spinal canal:
CM Type I (one)
This is the most common type. It’s typically diagnosed when the lower part of the cerebellum pushes downward into the space that holds the spinal cord by at least one-fifth of an inch.
Some people with a CM Type I don’t have any symptoms or they don’t develop symptoms until they are teenagers or adults. Doctors usually find out that teenagers and adults have a CM Type I while doing tests to find the cause of neurological symptoms such as headaches, dizziness, or balance problems.
CM Type II (two)
This happens when both the cerebellum and the lower part of the brain that connects to the spinal cord push into the hole where the brain meets the spinal cord. The part of the brain that connects the two halves of the cerebellum may be missing or only partially formed. Doctors can identify this condition before birth.
Infants with a CM Type II also have a myelomeningocele—a type of spina bifida that happens when the infant’s back bones don’t close properly around the spinal cord. A myelomeningocele usually causes a buildup of spinal fluid. This can cause swelling along with partial or complete paralysis of the body below the point where the spine didn’t close properly.
CM Type II can cause other symptoms like difficulty breathing, trouble with the gag reflex that helps prevent choking, and uncontrolled eye movements. CM Type II is also called Arnold-Chiari malformation.
CM Type III (three)
This is a rare but very serious condition identified at birth. In this condition, a large amount of brain tissue pushes through a hole or defect in the back of the skull. This creates a sac outside the skull filled with brain tissue and sometimes spinal fluid.
CM Type III is often life-threatening early in life and may require surgery. Infants may have other severe neurological problems—such as hydrocephalus, seizures, and delays in movement and learning.
CM Type IV (four)
This is a very rare type of CM that happens when the cerebellum doesn’t develop properly or parts of it are missing.
Other related CM types
Doctors are still working on defining these types:
- CM Type 0 is a rare CM type that happens when the brain and skull form normally, but spinal fluid buildup causes symptoms such as headaches, neck pain, dizziness, and problems with balance.
- CM Type 1.5 is a CM type that happens when both the cerebellum and part of the lower part of the brain extend lower than they should—more than in CM Type I but without the structural or developmental problems seen in CM Type II. This type is becoming more common due to doctors having access to more precise MRI imaging tests.
Who is more likely to get a Chiari malformation?
A CM often happens because the brain and spinal cord don't develop properly before birth. Doctors call this primary or congenital CM.
It’s also possible for a CM to develop later in life if spinal fluid drains too much due to traumatic injury, disease, or infection. This is called secondary or acquired CM. Congenital CM is much more common than acquired CM.
How is Chiari malformation diagnosed and treated?
Diagnosing CM
There is no genetic test, blood test, or screening that determines if an infant will be born with a CM. Doctors can use ultrasound imaging tests during pregnancy to see Chiari Type II once the problem is there, but no test can predict the condition before it develops. Since CM is associated with inherited conditions like spina bifida, children born with other developmental problems are often tested for CM.
To diagnose CM, a doctor does a physical exam and checks memory, thinking, balance, touch, reflexes, sensation, and movement. Doctors may also order imaging tests to detect skull problems or spinal fluid buildup inside the skull that can cause swelling and symptoms like headaches, vomiting, or changes in thinking.
Learn more about neurological diagnostic tests and procedures.
Treating CM
Treatment depends on symptoms and how serious they are. Milder versions of CM that don’t show symptoms and don’t interfere with daily life may only need regular checkups and imaging tests. If a CM is diagnosed during childhood or the teenage years, they may never have symptoms, or they could also develop symptoms later in life. Medicines can treat headaches and pain if symptoms are mild.
Surgery
Surgery is often the only treatment available to prevent nerve damage that can cause problems with moving, thinking, feeling, balancing, swallowing, or breathing. In most people with a CM, surgery can help by keeping symptoms from getting worse. Some people may need more than one surgery.
During surgery, surgeons remove a small piece of bone from the back of the skull (and sometimes the top of the spine) to give the brain more room and prevent symptoms caused by too much spinal fluid. Surgeons sometimes use a tiny electric tool that burns or shrinks parts of the cerebellum that are not needed, which frees up space for spinal fluid.
Surgery can also treat conditions associated with CM, such as when the spinal cord is pulled too tight and spinal fluid builds up in the brain (hydrocephalus). Hydrocephalus is usually treated with a shunt—a tube that drains extra spinal fluid to relieve pressure.
Infants born with a CM Type II often also have a type of spina bifida that happens when the back bones don’t close correctly around the spinal cord. Usually within the first few days after birth, a surgeon moves the nerves back into the spine, repairs the layers over them, and then closes the muscles and skin on the infant’s back.
What are the latest updates on Chiari malformation?
The National Institutes of Health (NIH), which includes NINDS, is the leading federal funder of research on the brain and nervous system, including disorders such as CM. NIH supports new and innovative research to better understand, diagnose, and treat CM.
Genetic studies
NIH researchers are studying certain gene changes that cause many problems with brain growth and development caused by CM, spinal fluid buildup, and other brain disorders. This work could lead to new tests and better treatments for CM and other developmental brain disorders.
Brain processes
The middle part of the brain helps control movement and the senses, and the lower part of the brain controls balance, breathing, and basic body functions. Researchers are trying to figure out how these two brain parts are formed, work properly, and communicate with each other. For example, NIH researchers studying how CM develops are using tiny fish called zebrafish whose embryos are see-through and develop quickly as a model system to study early formation of the human brain.
Other researchers are studying how growth signals guide development of the brain, skull, spine, and spinal cord. They are also trying to learn how gene changes or factors in a mother’s surroundings or health can affect how an infant’s brain and spine develop.
Making diagnoses clearer
Several NIH-funded research programs are hoping to better understand what causes CM. While imaging tests are usually the best way to diagnose a CM, scientists are also testing whether adding genetic and medical tests improves diagnosis.
Other NIH-funded research is improving methods to look inside the brain to help doctors diagnose CM as early as possible. Researchers are also using MRI scans to detect biological signs of disease that don’t show up in blood tests or genetic tests to help doctors decide which type of surgery will work best to treat various types of CM.
Long-term effects of surgery
NIH researchers are examining people who have syringomyelia, a spinal fluid-filled sac in the spinal cord that many people with CM Type II have. Not much is known about the long-term health effects of having surgery to treat syringomyelia. For example, this surgery may affect muscle strength, pain, and overall physical function.
To learn more about the effects of CM-related surgery, researchers are tracking symptoms, muscle strength, general level of function, and MRI scans for five years in people who receive standard syringomyelia treatment. They hope to learn more about what causes syringomyelia to start and get worse, along with what types of treatment relieve symptoms.
A recent NIH-funded research study looked at children with a CM Type I and syringomyelia one year after surgery to make more room for the brain and spinal cord. Those children who had surgery that added a patch of extra brain tissue to the brain’s outer covering to improve fluid flow had fewer and less severe symptoms after surgery and were less likely to need another surgery.
NIH continues to support research on these and other health conditions affecting brain growth and development to understand CM better and how to best diagnose, treat, and prevent it.
For more information on research about CM, check NIH RePORTER, a searchable database of current and past research projects funded by NIH and other federal agencies. RePORTER also has links to publications and resources from these projects.
For research articles and summaries on CM, search PubMed, which contains citations from medical journals and other sites.
How can I or my loved one help improve care for people with Chiari malformation?
Consider participating in a clinical trial so clinicians and scientists can learn more about CM. Clinical research with human study participants helps researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.
All types of study participants are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities. This helps make sure that study results apply to as many people as possible and that treatments will be safe and effective for everyone who will use them.
For information about participating in clinical research, visit the NINDS Clinical Trials site and NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with CM at ClinicalTrials.gov, a searchable database of current and past clinical studies and research results.
Where can I find more information about Chiari malformation?
Information may be available from the following sources: