Chiari Malformations
Chiari Malformations
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Azara Singh, MBBS, MD   

Charleston Area Medical Center, Charleston, WV 

Reviewed December 2022


Chiari malformations are a group of conditions. They may occur when these have not appropriately formed: 

  • The cerebellum  
  • Parts of the brainstem  

The cerebellum is a part of the brain that helps control: 

  • Balance  
  • Coordination  

Chiari malformations are congenital. This means they are present at birth.  

Chiari malformations sometimes cause a portion of the cerebellum to protrude. It can extend into the top of the spinal canal. It can press on the brainstem. It can also press on the upper part of the spinal cord.  

Malformations are divided into different types. These affect different structures. 

Not all Chiari malformations cause symptoms or need treatment. Sometimes they are found during an MRI (magnetic resonance imaging) or CT (computed tomography) scan for other reasons. These are often called incidental findings.


Disorder Overview


The skull base has a large opening. This opening is called the foramen magnum. This is where the brainstem leaves the head. It continues downwards as the spinal cord.  

Right above and slightly behind the opening, the cerebellum sits in a space. This space is called the posterior fossa. Cerebellum connections feed in and out of the brainstem. This is similar to ramps leading on and off the interstate. 

Fluid-filled spaces surround all these structures. The spaces are called ventricles. Ventricles contain cerebrospinal fluid (CSF). CSF bathes the brain and the spinal cord. It is then absorbed back into the ventricles. 

Chiari malformations are a group of disorders. They primarily affect the size and shape of: 

  • The cerebellum  
  • The posterior fossa 

These changes can cause pressure on the brainstem. They can block the flow of CSF.  

When CSF flow is blocked, it is like a block in a pipe. Upstream of the blockage, fluid builds up. This increases pressure. In this case, increased pressure occurs inside the skull. It can cause many symptoms.

Subtypes of Chiari Malformations

Chiari I Malformation

Chiari I is the most common type. This is often what people refer to when they use this term. Up to 1 in 1,000 people is diagnosed with a Chiari I malformation.  

In this subtype, the cerebellum’s “tonsils” protrude through the foramen magnum. They extend into the spinal canal. The term “tonsils” refers to the lowest part of the cerebellum. They are different from the tonsils in the mouth.  

It is usual for tonsils to protrude down past the foramen magnum by up to three millimeters. In babies, they can protrude as far down as six millimeters. Generally, if the tonsils protrude by five millimeters or more, the terms “Chiari I malformation” or “cerebellar tonsillar ectopia” are used.  

A Chiari I malformation can be asymptomatic. This means that it does not cause symptoms. It is still visible on imaging.  

Chiari I malformations can create symptoms in two ways:  

  • They can block CSF flow. This increases pressure within the skull.  
  • Pressure can result from the cerebellar tonsil pressing against: 
    • The brainstem  
    • The upper spinal cord

A small, collapsed space usually runs down the middle of the spinal cord. This is called the central canal. When CSF flow back to the brain is blocked, this space becomes enlarged. It fills with fluid. This enlarged, fluid-filled space in the spinal cord is then called a syrinx.

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Chiari II Malformation, or Arnold-Chiari Malformation

Chiari II is a more severe type of Chiari malformation. In this case: 

  • The posterior fossa is smaller than usual.  
  • The foramen magnum is larger than usual. 
  • A larger part of the cerebellum protrudes out into the spinal canal.  

Blocking the flow of CSF leads to hydrocephalus. Hydrocephalus means the fluid-filled ventricles in the brain are enlarged.

Chiari II can also lead to myelomeningocele. Myelomeningocele means the spinal cord and its coverings protrude through a space in the spinal column of vertebrae. In severe cases, they may protrude out of the skin.

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Chiari III Malformation

Chiari III is a very rare and severe type of Chiari malformation. In this case:

  • The bony skull does not form properly.
  • The cerebellum and its covering membranes protrude out.

Chiari III is very serious. Infants with Chiari III malformations may have life-threatening problems.

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Asymptomatic Chiari I Malformation 

This type typically does not cause symptoms. It is often found incidentally during a CT or MRI of the brain for other reasons. 

Symptomatic Chiari I Malformation 

When Chiari I malformations cause symptoms, they may include:


Headaches often occur at the back of the head. They worsen when coughing or straining.

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Symptoms caused by pressure on the cerebellum.

These include: 

  • Uncontrollable jerking movements of the eyeballs (nystagmus) 
  • Unsteadiness of the head and the trunk when sitting or standing (ataxia). Ataxia may also cause coordination problems. These occur when trying to perform fine movements with the hands. 
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Symptoms caused by pressure on the brainstem.

These include: 

  • New changes in one’s voice and difficulty speaking 
  • Difficulty swallowing and frequent choking 
  • Excessive drooling or gagging 
  • Weakness or tightness in the limbs 
  • Ringing in the ears or difficulty hearing 
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Symptoms caused by blocking the flow of CSF (hydrocephalus).

These include: 

  • New behavioral changes, such as: 
    • Irritability 
    • Sleeping much more than usual 
    • Not feeding well  
  • Repeated vomiting 
  • Developmental delays 
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Symptoms caused by pressure on the spinal cord by a large syrinx.

These include: 

  • Difficulty walking 
  • Increased tightness in the legs 
  • Weakness in the arms 
  • Numbness or tingling in the limbs 
  • Pain that shoots down the arm or leg 
  • Curvature of the spine (scoliosis) 
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Symptomatic Chiari I malformations may cause disability. They rarely cause death unless the following go untreated for a long time: 

Chiari II Malformation, or Arnold-Chiari Malformation 

Symptoms of this type include:

A myelomeningocele.

This nearly always occurs. It is a type of spina bifida. The following do not close completely around the spinal cord during formation: 

  • The bony vertebrae 
  • Spinal cord coverings 
  • The skin (sometimes) 

Myelomeningoceles can cause: 

  • Weakness or paralysis 
  • Tightness in the limbs 
  • Severe constipation 
  • Severe difficulty emptying the bladder 
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Difficulty breathing, difficulty swallowing, and choking spells.

These are often seen in babies.

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Worsening hydrocephalus.

This is caused by increased CSF pressure within the skull.

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Sometimes, changes in the structure of the brain cause seizures.

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Chiari III Malformation 

Children with Chiari III malformations may have symptoms associated with Chiari I and II malformations. 

Symptoms of this type include: 

  • Difficulty breathing.  
  • Other neurological problems. These include:  
    • Epilepsy  
    • Severe developmental delays 

Chiari II and III malformations must be treated by surgery. Otherwise, they can cause severe medical problems or death. 



We do not know exactly what causes Chiari malformations. Scientists are studying possible genetic causes. Several family members may have Chiari I malformations. This suggests a genetic cause.  

A lack of folic acid and vitamin B12 during pregnancy may increase the risk of a baby being born with Chiari II malformations. For this reason, these are given to pregnant mothers: 

  • Folic acid  
  • Vitamin B12 

Long-term anti-seizure medication can also reduce levels of folic acid in the body. All young women with epilepsy who are on anti-seizure medication should take a daily folic acid supplement. They should do so even before they plan to get pregnant.  


Chiari I malformations are usually diagnosed with an MRI. Images are taken of: 

  • The head  
  • The neck 

The doctor will look at the spinal canal. They will check how far down the cerebellar tonsils protrude. They will also check to see if CSF flow is blocked.  

Once the Chiari I malformation is diagnosed, a spine MRI may be done. It can identify whether there is a syrinx in the spinal cord. 

In a Chiari I malformation with mild symptoms, the MRI may be repeated after a year or so. This is to see if it changes or worsens. In asymptomatic Chiari I malformations, repeat imaging is not usually needed.   

Chiari II and III malformations are often initially seen on ultrasounds during pregnancy. MRI confirms them.  

Your child’s neurologist may recommend additional genetic testing for Chiari II and III malformations. For example, they may recommend whole exome sequencing. This looks at a large part of your child’s genetic material. This may be a helpful test, particularly when planning future pregnancies. It can identify possible genetic causes.


Specific Chiari malformations require surgery. Surgery is not required for asymptomatic Chiari I malformations. It may not always be necessary for people with mild symptoms.  

Surgery is recommended if there is: 

  • Hydrocephalus 
  • Impaired coordination (ataxia) 
  • Pressure on the brain stem 
  • Weakness of the limbs

The most common type of surgery for Chiari I malformations is posterior fossa decompression. The surgeon makes an opening in the bone. Sometimes, they also make an opening in the membranes around the cerebellum. This allows more room. It prevents crowding of the brainstem. 

These always require surgery: 

  • Chiari II malformations 
  • Chiari III malformations 

Surgery is often done in infancy or early childhood.  

Possible side effects of surgery include:  

  • Head and neck pain. 
  • Injury to blood vessels in the area. 
  • Formation of a pseudo-meningocele. This is a collection of CSF within soft tissues of the head and neck.

Surgery involves opening up the meninges. These are the coverings of the brain. So, there is a risk of infection. Surgery can inflame the meninges. (This is meningitis.) This risk is minimized by maintaining a sterile environment during surgery. 

Following surgery, therapy may be recommended. It can help children build: 

  • Strength  
  • Coordination

Children can benefit from: 

  • Physical therapy 
  • Occupational therapy 
  • Speech/feeding therapy (if needed)

Many children with Chiari II malformations are referred to a special myelomeningocele clinic. With a single visit, they can see:  

  • A neurologist 
  • A physical medicine specialist 
  • A gastroenterologist 
  • A therapist  


After surgery for a symptomatic Chiari I malformation, symptoms can improve. These symptoms include:  

  • Headache 
  • Dizziness 
  • Pain 
  • Difficulty swallowing 
  • Hearing problems  
  • Symptoms related to hydrocephalus 

Some symptoms may take longer to improve. For example, these may persist: 

  • Limb weakness 
  • Limb tightness 

It is also possible that symptoms will not go away completely. Particularly, those related to pressure on the spinal cord may persist. 

After repairing the myelomeningocele, patients may still have symptoms. These include:  

  • Weakness 
  • Constipation 
  • Difficulty emptying the bladder 
  • Changes in sensation over the lower half of the body  

Patients with mild symptomatic Chiari I malformations will likely be able to function independently. They usually require little, if any, assistance in their daily activities.  

Patients with more severe Chiari I and II malformations may still need some assistance after surgery. Specifically, they may need assistance with the following:  

  • Moving around  
  • Toileting  

Their environment can be modified to support their independence. For example, these can be helpful: 

  • Installing rails for getting in and out of the bathtub  
  • Using assistive devices to get around 

Ramps make schools and other public spaces more accessible. It may be beneficial to have a ramp installed at home as well.  

Some children have disabilities because of Chiari malformations. For them, setting up a 504 plan at school is very helpful. This plan identifies the following:  

  • Their needs  
  • How the school can accommodate their needs 

Needs will vary from child to child. They may include: 

  • Reducing the need to transfer from one classroom to another (if the child has difficulty moving around) 
  • An aide to help with toileting, and regular toileting breaks built into the school day 
  • Limiting screen time if it worsens headaches 
  • Providing extra time for assignments and tests  

These and other accommodations can be helpful. However, each child’s needs differ. The 504 plan should be tailored to their individual needs. That way, they can participate fully at school.   

Some children may need to have a catheter placed. This is a narrow tube. It can help them empty their bladder several times a day. Catheters may be particularly necessary for children with Chiari II malformations after surgery removes the myelomeningocele. Older children can learn to catheterize themselves.  

Children may also need periodic enemas. This helps them empty their bowels. They may also need help getting around. This depends on the extent of their weakness. 

The goal of physical and occupational therapy is to help them get stronger. It is also meant to identify how their surroundings can be modified to support their independence.   

Children with all Chiari malformations may need medicine. Medicine can manage:  

Children with Chiari III malformations may need medicine to control seizures. They may also need other modifications at school and home.  


Bobby Jones Chiari & Syringomyelia Foundation

The mission of the Bobby Jones Chiari & Syringomyelia Foundation (Bobby Jones CSF) is to advance knowledge through research and to educate the medical, allied sciences and lay communities about Chiari, syringomyelia and related disorders, including Idiopathic Intracranial Hypertension (IIH). Patient information includes the Chiari Malformation & Syringomyelia Handbook which is an excellent resource for patients and medical professionals. Join the online community to connect with patients, families, friends and caregivers for support and inspiration.  

Conquer Chiari

Conquer Chiari is dedicated to improving the experiences and outcomes of Chiari patients through education, awareness, and research. Conquer Chiari resources for Pediatric Chiari include Handouts and School Resources

Family Stories

Patient stories from those living with Chiari, Syringomyelia and related disorders are highlighted in the video archive of the Bobby Jones Chiari & Syringomyelia Foundation (Bobby Jones CSF) website.

Conquering Chiari shares pictures and stories that represent just a glimpse of the many children affected by Chiari on the Faces of Chiari page. More pediatric stories can be found on the Chiari Stories page.

Child Neurology Foundation (CNF) solicits resources from the community to be included on this webpage through an application process. CNF reserves the right to remove entities at any time if information is deemed inappropriate or inconsistent with the mission, vision, and values of CNF. 

Research for Chiari Malformation (birth to 17 years).

These are clinical trials that are recruiting or will be recruiting. Updates are made daily, so you are encouraged to check back frequently. is a database of privately and publicly funded clinical studies conducted around the world. This is a resource provided by the U.S. National Library of Medicine (NLM), which is an institute within the National Institutes of Health (NIH). Listing a study does not mean it has been evaluated by the U.S. Federal Government. Please read the NLM disclaimer for details.    

Before participating in a study, you are encouraged to talk to your health care provider and learn about the risks and potential benefits.

For more information about participation in clinical trials, check out our education hub on the topic here

Information for research and clinical trials specific to Chiari Malformation can be found on Bobby Jones Chiari & Syringomyelia Foundation and Conquer Chiari websites. 


The information in the CNF Child Neurology Disorder Directory is not intended to provide diagnosis, treatment, or medical advice and should not be considered a substitute for advice from a healthcare professional. Content provided is for informational purposes only.  CNF is not responsible for actions taken based on the information included on this webpage. Please consult with a physician or other healthcare professional regarding any medical or health related diagnosis or treatment options. 


McClugage SG, Oakes WJ. The Chiari I malformation. J Neurosurg Pediatr. 2019 Sep 1;24(3):217-226. PMID: 31473667. 

Saletti V, Farinotti M, Peretta P, Massimi L, Ciaramitaro P, Motta S, Solari A, Valentini LG. The management of Chiari malformation type 1 and syringomyelia in children: a review of the literature. Neurol Sci. 2021 Dec;42(12):4965-4995. Epub 2021 Sep 30. PMID: 34591209. 

Spina Bifida Association [Internet]. Arlington, VA: 2022. Available from: 

Hadley DM. The Chiari malformations. J Neurol Neurosurg Psychiatry. 2002 Jun;72 Suppl 2(Suppl 2):ii38-ii40. PMID: 12122202; PMCID: PMC1765588. 

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