What is Chiari Malformation?

Chiari malformation is a rare condition that affects the back part of the head where the brain and spinal cord connect. It causes some of the brain tissue in the lower part of the brain (called the cerebellum) to be pushed downward through the opening at the base of the skull into the spinal canal. This can put pressure on parts of the brain and spinal cord, block the normal flow of spinal fluid in and around the brain, and lead to a buildup of spinal fluid in the spinal cord. 

In most cases, Chiari malformation develops before birth (congenital). The exact cause of Chiari malformation is not always known but may involve differences in the way the skull develops. Rarely, Chiari malformation can develop (acquired) due to injury, infection, excessive drainage of spinal fluid, or other conditions that affect the skull or brain tissue over time. 

There are four different types of Chiari malformation. They are described below. 

Types of Chiari Malformation

There are four types of Chiari malformations. They are categorized by which parts of the brain are pushed into the spinal canal and the severity of the condition: 

• Chiari malformation type 1 – This is the most common type of Chiari malformation. The lower part of the cerebellum (called the cerebellar tonsils) dips down through the bottom of the skull and into the spinal canal, but the brainstem stays in place. This type is most often congenital, meaning it develops before birth, as the skull and brain are growing. Chiari malformation type 1 is often not found until a child is a teen or young adult. Many individuals with Chiari malformation type 1 may never know that they have a Chiari malformation unless they have a scan. People with Chiari malformation type 1 often have no symptoms and need no treatment.
• Chiari malformation type 2 – This type, also known as Arnold-Chiari malformation, develops before birth and is seen in babies with spina bifida, a condition where the spinal cord does not fully develop. Part of the cerebellum and brainstem are pushed down through the opening at the bottom of the skull and into the spinal canal. Most children with Chiari malformation type 2 do not need surgery to address the Chiari malformation.
• Chiari malformation type 3 – This is a severe and rare type of Chiari malformation. It is usually diagnosed in newborns. The cerebellum, brainstem and sometimes other parts of the brain are pushed down through the opening at the bottom of the skull. In rare cases, some parts of the brain may poke out through the back of the head or neck. A baby with Chiari malformation type 3 may not live long. Children who do survive will have severe disabilities.
• Chiari malformation type 4 – This is a very rare and severe type of Chiari malformation in which the brain doesn’t fully develop, or part of the brain is missing. Most babies with Chiari malformation type 4 do not survive.

Because Chiari malformation type 3 and type 4 are extremely rare, the information that follows focuses on diagnosis and treatment of Chiari malformation type 1 and type 2 at Children's Hospital of Philadelphia's Neuroscience Center. 

Signs and symptoms of Chiari malformation

Most children with Chiari malformation type 1 often have no symptoms, or their symptoms develop slowly over time and are not recognized until their teen or early adult years. In many cases, they are diagnosed after having a magnetic resonance imaging (MRI) scan for another problem. 

Chiari malformation type 1 symptoms may include: 

• Headaches
• Pain in the back of the head or neck, especially when coughing, laughing or sneezing
• Trouble swallowing
• Balance issues
• Weakness or abnormal movements
• Rapid eye movements
• Hoarseness or trouble speaking
• Abnormal shape of the spine (scoliosis)
• Breathing problems, especially during sleep (sleep apnea)
• Trouble walking or pain in the arms or legs

Chiari malformation type 2 symptoms may include: 

• Build-up of fluid in the brain (hydrocephalus)
• Weak cry
• Trouble swallowing
• Breathing problems
• Problems with nerve function in the throat and tongue

Causes of Chiari malformation

Chiari malformation type 1 is usually present at birth (congenital). The exact cause of a congenital Chiari malformation type 1 is not known. 

In rare cases, some people develop Chiari malformation type 1 after birth. This is called acquired Chiari malformation. 

Chiari malformation type 2 most often occurs in children with the most serious form of spina bifida, called myelomeningocele. In this condition, the backbone and spinal canal do not close before birth. 

What are the risk factors for Chiari malformation?

Doctors do not always know what causes Chiari malformation, but some factors can make it more likely to develop. A person has a higher chance of having Chiari malformation if a biological relative has it, which suggests that it runs in some families and genetics may play a role. Other risk factors include conditions that affect how the skull or brain forms before birth, like spina bifida or issues with spinal fluid flow. 

What are the complications of a Chiari malformation?

In most people, Chiari malformation causes no symptoms and does not require treatment. However, for others, the condition can worsen over time.  

Conditions associated with Chiari malformation:  

• Syringomyelia (syrinx): Some children develop a condition where a fluid-filled cyst, called a syrinx, forms within the spinal cord. As the syrinx grows, it can put pressure on the nerves, causing pain, muscle stiffness, weakness, sensation changes, and bowel and bladder problems.
• Spina bifida: This is a condition where the spinal cord or its protective covering does not fully develop, leaving part of the spinal cord exposed. This can lead to serious issues, including paralysis. Children with Chiari malformation type 2 often have the most common and serious form of spina bifida called myelomeningocele.
• Hydrocephalus: This happens when excess fluid builds up in the brain, which can affect thinking and brain function. Some children with hydrocephalus may need a shunt, a small flexible tube that helps drain the extra fluid to another part of the body where it can be safely absorbed.
• Tethered cord syndrome: In this condition, the spinal cord ends at a lower level than expected and places tension on the spinal cord, pulling and stretching the nerves. This can lead to nerve and muscle damage in the lower body. 

For those affected by these complications, early diagnosis and treatment can help manage symptoms and improve quality of life. 

Testing and diagnosis for Chiari malformation

At Children's Hospital of Philadelphia's Neuroscience Center, your child’s care begins with a comprehensive, personalized assessment of their medical history and symptoms.

The diagnosis of Chiari malformation is made after a physical examination and one or more of the following imaging tests:

• Magnetic resonance imaging (MRI) – An MRI uses powerful radio waves and magnets to create a detailed picture of the brain, spinal cord or other organs. These pictures can identify many different types of abnormalities in the brain and help in the diagnosis of your child’s particular form of Chiari malformation. MRI is a safe, painless test that produces detailed images of structural differences in the brain that may be contributing to your child’s symptoms. It can also provide images of the cerebellum and determine whether it extends into the spinal canal. MRI may require sedation in young children to help them stay still and comfortable. Your care team can discuss this further with you.
• Computed tomography (CT) ­– A CT scan uses a series of X-rays to create a cross-sectional image of the body. The CT machine makes images that are more detailed than a regular X-ray.

In a child with no symptoms, Chiari malformation may be diagnosed when imaging tests are done for other reasons. 

Chiari malformation treatment

At the Neuroscience Center, the goal of treatment is to stop symptoms from interfering with a child’s normal growth and development, with as few treatment-related side effects as possible. Treatment for Chiari malformation depends on the severity and characteristics of your child’s condition.  

• Medical Management – If your child has no symptoms, your doctor will likely recommend no treatment other than regular physical examinations and MRIs to monitor the growth and development of your child’s brain, spinal cord, skull and backbones. If headaches or other types of pain are the primary symptom, your doctor may recommend pain medication.
• Surgery – If your child has symptoms, they will likely need surgery to relieve pressure on the brain or to restore the normal flow of spinal fluid. The specific type of surgery your child’s doctor recommends will depend on:
  • Your child’s age, overall health and medical history
  • The severity of your child’s symptoms
  • The type of Chiari malformation

Chiari malformation surgery

Chiari is an anatomical issue, and sometimes a surgical solution is required to relieve symptoms and improve quality of life. When surgery is needed, we offer a range of advanced procedures, including: 

• Extradural Chiari Decompression – A neurosurgeon removes a small portion of bone at the back of the skull to create more space and improve spinal fluid flow. This lower-risk procedure typically requires less time spent in the hospital after surgery and it has excellent long-term outcomes, with little need for additional surgery.
• Intradural Chiari Decompression – Similar to extradural decompression, this procedure also involves removing a small amount of bone at the back of the skull. In addition, the surgeon makes an incision in the brain’s outer covering (called the dura) and sews in a patch (called a duraplasty) to further increase space and improve spinal fluid flow. 

In rare cases, more complex surgical interventions may be required for Chiari malformation. These may include: 

• Occipital-Cervical Fusion – In this surgery, screws and bone grafts are used to join the skull and spine to correct cervical instability and prevent injury.
• Ventral Decompression – This surgery is performed through the nose or mouth and relieves pressure on the brain and spinal cord caused by Chiari malformation.
• Spinal Shunting – In this procedure, a small, hollow tube (shunt) is placed in the spine to drain excess cerebrospinal fluid. The shunt redirects the fluid to another part of the body, such as the abdomen, where it can be safely reabsorbed. 

Each child’s treatment plan is carefully tailored to their unique needs, ensuring they receive the most effective and least invasive care possible. 

Learn more about our comprehensive treatment options in our Chiari Malformation FAQ Guide for Caregivers.

What’s the long-term outlook for a Chiari malformation?  

While treatments are available to manage Chiari malformation, there is no cure. A child will always live with it and may need to be followed by a neurosurgeon and/or neurologist.  

However, when we provide the right care for a child, the outcome can be incredible. That is why a thorough evaluation is so important. It helps us find the right care for each child. Most kids we treat — whether by non-surgical methods or surgery — experience fewer symptoms or no longer have any symptoms. Classic Chiari symptoms respond very well to surgery. For example, some of our patients who were in pain for years now live pain-free.