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Chiari Malformation

  • At Boston Children’s Hospital, we have already helped many infants, children and adolescents who have been diagnosed with a Chiari malformation, an abnormality in the meeting of the brain and the spinal cord at the base of the child’s skull.

    There are four types of Chiari malformation. Type I is by far the most common form of the condition in children, while type II is typically only seen in children with spina bifida. The other types of Chiari malformation are extremely rare.

    For the purposes of this webpage, the information you will read below focuses only on type I and type II Chiari malformation.

    Here are some of the basics about Chiari malformation:

    Type I:

    • Type I Chiari malformation occurs in around 3 percent of the general population. However, since individuals with this condition often don’t show symptoms and go undiagnosed, it’s difficult to say exactly how many people actually have it.
    • Most children with type I Chiari malformations have no signs or symptoms and are only diagnosed when they get a magnetic resonance imaging (MRI) scan for another problem.
    • When symptoms occur, they typically present in late childhood or early adulthood and usually include neck pain. Other symptoms may include balance problems, sleep apnea (a common disorder that causes pauses in breathing during sleep) and swallowing difficulties.
    • The Chiari malformation can also cause fluid to accumulate in the spinal cord – a condition called syringomyelia – which can cause scoliosis in children. Syringomyelia can also make it harder for the brain to process and organize sensory information that comes from the surrounding environment.
    • If the Chiari malformation is not causing problems for the child, no treatment is needed. When symptoms do occur, treatment generally involves surgery to relieve pressure on the cerebellum, brain stem and spinal cord.

    Type II:

    • Type II Chiari malformation occurs when the tissue from the cerebellum, along with the brain stem itself, protrude downward through the base of the skull into the upper spinal canal.
    • Type II Chiari malformation almost always affects children who have spina bifida. It is present at birth (congenital).
    • Most children with this form of the condition require treatment for buildup of fluid in the brain (hydrocephalus).

    How Boston Children’s approaches Chiari malformation

    Since a child with a type I Chiari malformation may not have symptoms, the safest approach is to leave it untreated and perform a follow-up evaluation by MRI and examination if necessary. However, for symptomatic patients, or those who have developed an accumulation of fluid in the spinal cord, we typically recommend surgical treatment.

    Chiari malformation: Reviewed by Benjamin C. Warf, MD
    © Children’s Hospital Boston; posted in 2012

  • At Boston Children’s Hospital, we understand that a diagnosis of a brain abnormality such as Chiari malformation comes with many questions and concerns for parents and families. We’ve provided straightforward information about Chiari malformation here, and when you meet with our team of doctors, they’ll be able to explain your child’s condition and options fully. Learning more about your child’s diagnosis and treatment options is a great way to become an active participant in his medical management.

    What is the difference between type I Chiari malformation and type II Chiari malformation?

    Type I and Type II Chiari malformation both cause brain tissue to protrude into the space at the back of the skull.  However, there are a few differences that distinguish these two conditions:

    • Type I Chiari malformation occurs because of a developmental abnormality and it can affect any child.  Type I involves the lower part of the cerebellum (also known as the “tonsils”).
    • Type II Chiari malformation is specific to children that have spina bifida, a congenital defect that occurs when a baby is born with an open and unprotected spinal cord at the bottom of the spine. Type II involves a greater amount of brain tissue than type I.


    What causes Chiari malformation?

    The causes of type I and type II Chiari malformations are different.

    Type I

    • In the past, it was thought that type I Chiari malformation was congenital, meaning that a child was born with the abnormality. As MRI imaging became more commonplace, doctors saw that the malformation actually develops due to a mismatch between the rate of growth of the skull and the rate of growth of the brain, causing the bottom of the cerebellum to push out of the base of the skull into the spinal canal over time. 
    • Researchers have also observed links to genetics and developmental syndromes.

    Type II

    • Almost all children with type II malformations have spina bifida.  As a result, many of these children require treatment for hydrocephalus (build-up of fluid in the brain).

    Signs and symptoms

    What are the symptoms of Chiari malformation?

    The symptoms of type I Chiari malformation and type II Chiari malformation are different.

    Type I:

    • The symptoms of type I Chiari malformation and their degree of severity vary from person to person. In most cases, individuals with type I Chiari are asymptomatic and don’t even know that they have it. But if the malformation is severe, the following symptoms may occur:
    • One of the primary symptoms of type I Chiari malformation is pain in the lower back of the head into the neck (also known as suboccipital pain). This is a headache that tends to come on quickly and is made worse by any activity that increases pressure in the brain, such as coughing and sneezing.
    • In some cases, the cerebellar tissue can extend down low enough into the spinal canal that it blocks the normal flow of cerebral spinal fluid (CSF) or puts too much pressure on the brain or spinal cord. This can affect the child’s nervous system and cause symptoms such as dizziness and problems with balance and coordination.
    • Chiari I can also cause fluid to build-up in the spinal cord (syringomyelia), which may lead to scoliosis. The reason for this is still unknown, but many doctors believe that it’s because the fluid gets blocked by the malformation and then collects in the spinal cord. The harmful pressure of the fluid’s pressure on the nerve cells weakens the muscles and leads to a curvature of the spine. Untreated, it can lead to other neurological deficits.

    Other symptoms of type I can include:

    • Swallowing difficulties
    • Sleep apnea
    • Rarely, but occasionally, cough syncope can occur. Children who experience a cough syncope lose consciousness for a brief period of time and pass out after coughing or sneezing.

    Type II:

    Build-up of fluid in the brain (hydrocephalus) occurs in the majority of children with type II Chiari malformation. Older children may notice head pain with a cough or a sneeze, bending over, strenuous physical activities, or straining to have a bowel movement.

    More frequently, children with type II Chiari malformation have problems with the function of the nerves in the brain stem, such as:

    • Weakness of vocal cords
    • Swallowing difficulties
    • Breathing irregularities
    • Serious changes in the function of nerves of the throat and tongue
  • Boston Children’s Hospital, we know that an early and accurate diagnosis of your child’s Chiari malformation is the first step to efficient and effective treatment.

    How is Chiari malformation diagnosed?

    The diagnostic tests your child might require include:

    • Magnetic resonance imaging (MRI): the main tool in diagnosing Chiari malformations, thisimaging procedure uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of the body’s organ and brain structure
    • If the lower part of your child’s cerebellum (the part of the brain that controls balance, coordination and muscle movement) is displaced by more than 5 or 6 millimeters, your radiologist will typically make a diagnosis of a Chiari malformation. If there are symptoms of headache, other neurological dysfunction, or a build-up of spinal fluid, your child should be assessed by a neurosurgeon to determine if your child needs surgery for the malformation. 

    A Chiari malformation has been diagnosed in my child, but there are no obvious symptoms. What should we do? 

    Your child should be examined by a neurologist or neurosurgeon to determine if there are any neurological abnormalities. The neurologist will also assess the severity of your child’s malformation.

    If the malformation is minimal and there are no symptoms, we do not recommend treatment. If the malformation is pronounced and the child is young, follow-up may be more frequent, both clinically and by MRI.

    My child has scoliosis and a build-up of spinal fluid, but feels perfectly fine and has no other symptoms. Does my child need an operation?

    If scoliosis is present, its progression to a curve greater than 35 degrees may mean that spinal fusion will become necessary. We try to get surgery done before curves worsen in order to lessen the likelihood of the need for a spinal fusion later on.

    I have been told that my child has an occult tethered spinal cord in association with a Chiari malformation and that several operations will be necessary to treat it. Is this true?

    A child with a type I Chiari malformation almost never has a tethered spinal cord and we do not believe that such surgical explorations are needed. If your child has a type II Chiari malformation, the tethered spinal cord may occur as a result of spinal fluid build-up (syringomyelia) and not the malformation itself. In these cases, the alternative causes of tethered spinal cord will need to be explored further.

  • All of the members of the Center for Head, Neck and Skull Base at Boston Children's Hospital have extensive experience caring for children with Chiari malformation. Our specialists are dedicated to anticipating any complications that your child may experience and developing the best therapeutic plans to manage them.

    While no medical procedure is a guaranteed success, surgery for Chiari malformation is one of the most successful operations that pediatric neurosurgeons do and we can be optimistic with the patients and families about its outcome.

    What are the goals of treatment?

    The overall goals of treatment for type I and type II Chiari malformation are the same:

    • Relieve the pressure on the brain and spinal cord
    • Reestablish normal fluid circulation through and around the area

    How is Chiari malformation treated?

    During surgery, your child's neurosurgeon attempts to relieve the pressure on thecerebellum, brain stem and spinal cord in order to reestablish normal circulation of the fluid in the area. Here are the typical steps involved:

    Because the pressure of the bone is one of the most important causes of the compression, the neurosurgeon removes a bit of bone from the lowest part of your child's skull.

    The firm covering of the brain and spinal cord tissues (also known as the dura) are then opened and widened to make space for the fluid to circulate around the area.

    To reduce crowding in lower part of the cerebellum, surgeons use electrical forceps to shrink the tissue. This maneuver is safe and causes no neurological damage.

    Finally, if your child has a build-up of spinal fluid, we inspect the opening under the cerebellum where the cerebrospinal fluid normally exits to make sure that it is now clear of scar tissue and that fluid can circulate normally through the area. Sometimes, a small tube may be placed into this opening, like a doorstop, to keep it open.

    What are the chances that the surgery will treat the build-up of spinal fluid successfully?

    The surgery has a high success rate.

    • Virtually eliminated in 50 percent of children
    • Substantially reduced in another 45 percent
    • Stabilized in the remaining 5 percent

    Will the Chiari malformation recur as my child grows?

    Rarely, a Chiari malformation can reappear in children who were operated on under the age of 6 if their skull bone re-grow and recompress the area, or if there are other associated causes of the malformation.

    How long will the surgery take and how long will my child be in the hospital?

    Depending on what needs to be done, the surgery and operating time can take from two to four-and-a-half hours. Your child will be in the hospital for approximately four-and-a-half days, including the day of surgery.

    What are the immediate aftereffects of the operation?

    Your child will typically be awake and talking right after the operation, but will have headache, neck pain and nausea for the next 48 hours. We'll keep your child comfortable with medications to deal with each of these problems. Your child will probably begin to eat and get out of bed one to two days after the operation.

    Does my child need head protection after the operation, and will he have any long-term limitations after the surgery?

    No head protection is needed, since there are strong and thick muscles at the base of the back of the neck that protect the area. Many doctors allow their postoperative patients to participate in all activities including football, lacrosse, soccer, etc.

  • At Boston Children’s Hospital, important technical breakthroughs are taking place in the approach to treating Chiari malformation. 

    Improving outcomes for surgical treatment of syrinx

    Boston Children’s is currently involved in a multi-institution study looking at the way Chiari malformation treated, specifically when treatment is warranted because of fluid cavity in the spinal cord (syrinx). 

    As of right now, there is no standardized practice for the surgical treatment of syrinx. Some clinicians take a minimalist approach and believe that removal of the bone is all that’s necessary to fix the problem. The more mainstream medical consensus agrees that opening the spinal sac and sewing in a patch graft must be done in addition to removal of the bone.  While this method has a higher success rate, the additional steps add further potential for complication and increase the hospital stay and the recovery.

    Boston Children’s is participating in a national trial that focuses on collecting data on every patient that undergoes surgery to have their Chiari malformation treated for syrinx. The collective findings will go into a national database, and after information on hundreds of patients is collected, we will start looking at the specific outcomes of each procedure.

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