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Chiari Malformation Fast Facts

Chiari malformation is a condition in which part of the brain protrudes abnormally through the base of the skull and into the spinal canal.

In severe cases, chiari malformation may cause symptoms such as headache, dizziness, or balance problems.

In some cases, chiari malformation may cause no symptoms.

At one time, chiari malformation was thought to occur in about 1 in every 1,000 people. With recent developments in diagnostic technologies, the condition is being diagnosed more often and may be much more common than originally thought.

Chiari malformation is more common in women than in men. One type of the condition is more common in people of Celtic ancestry.

Some types of chiari malformation are linked to other central nervous system conditions such as spina bifida, syringomyelia, and tethered cord syndrome.

Chiari malformation occurs when part of the brain called the cerebellum develops in an abnormal position.

What is Chiari Malformation?

Chiari malformation occurs when part of the brain called the cerebellum develops in an abnormal position. The cerebellum is at the base of the brain and normally sits above the opening in the base of the skull through which the spinal cord passes. In the case of chiari malformation, part of the cerebellum protrudes through the opening and into the spinal canal.

In some cases, chiari malformation causes no symptoms and may go undetected. In more severe cases, pressure on the cerebellum, which controls balance, results in a range of symptoms. In the most severe cases, symptoms and complications can be life-threatening.

Symptoms of Chiari Malformation

Symptoms associated with chiari malformation vary depending on the severity of the condition and the part of the cerebellum and other tissues that are affected. Common symptoms include:

  • Headache
  • Neck pain
  • Balance problems
  • Dizziness
  • Muscle weakness
  • Numbness in the extremities
  • Ringing in the ears or other hearing problems
  • Vomiting
  • Difficulty swallowing
  • Speech difficulties

Types of Chiari Malformation

Chiari malformation is classified according to the severity of the malformation and the part of the central nervous system affected.

Type I. In this type of malformation, only the lower part of the cerebellum extends through the opening in the skull. This type of chiari malformation may cause no symptoms, and when symptoms do occur, they may not develop until adolescence or adulthood.

Common symptoms of chiari malformation type I  include:

  • Headache
  • Neck pain
  • Balance difficulties
  • Dizziness
  • Numbness or tingling in the hands or feet
  • Problems with swallowing or speaking

Type II. In this type, the cerebellum and brain stem protrude through the opening in the skull. Sometimes the cerebellum is also abnormally developed or partially missing. Symptoms of this type are more severe and may be life-threatening. Symptoms typically appear during childhood and require surgery. This type is commonly associated with spina bifida, in which the spinal canal does not develop properly before birth.

Symptoms of chiari malformation type II may include:

  • Breathing difficulties
  • Difficulty swallowing
  • Muscle weakness
  • Abnormal eye movements

Type III. This type is characterized by an abnormal opening in the back of the skull through which part of the cerebellum, brain stem and/or other central nervous system tissue protrude. This severe form of chiari malformation is rare and life-threatening.

Symptoms of chiari malformation type III may include:

  • Mental disabilities
  • Physical developmental delays
  • Seizures

Type IV. In this type, the cerebellum does not protrude through the skull but is abnormally developed or partially undeveloped.

What Causes Chiari Malformation?

Chiari malformation happens when part of the cerebellum and/or brain stem is not protected by the skull as it usually is. The disorder occurs when the part of the skull that normally houses the cerebellum is deformed, resulting in increased pressure that forces part of the brain through the opening in the base of the skull and into the spinal canal. When the deformation is minor, the central nervous system (CNS) may continue to function normally, and no symptoms result.

A potential complication of chiari malformation is disruption of cerebrospinal fluid circulation through the CNS. This fluid protects and nourishes the brain and spinal cord, and if its circulation is impaired, symptoms can result. Excess fluid may build up in and around the brain, causing damaging pressure and disruption of nerve-cell function.

In some cases, damage to (or pressure on) the cerebellum or brain stem can cause other symptoms.

Chiari malformation type II is very often associated with spina bifida. In this disorder, the spinal cord and bones of the spine fail to develop properly before birth, and some central nervous system tissue protrudes through an abnormal opening in the spinal column. This condition is called myelomeningocele.

Is Chiari Malformation Hereditary?

Studies suggest that chiari malformation, as well as associated central nervous system disorders such as spina bifida and hydrocephalus, have an inherited component. These disorders seem to run in some families, and an individual is at increased risk if a close relative has also had one of the disorders.

Research into a possible genetic cause of chiari malformation in ongoing. Preliminary research has identified a genetic variation that may be associated with chiari malformation and other related disorders, but more research is needed to confirm the connection.

How Is Chiari Malformation Detected?

Because chiari malformation is often associated with disorders such as spina bifida and hydrocephalus, babies with these disorders are typically examined for chiari malformation. In some cases, the malformation may be visible on ultrasound scans before birth.

Early detection of mild cases of chiari malformation may be more difficult. If you experience any of the symptoms associated with the disorder, you should consult a medical professional.

How Is Chiari Malformation Diagnosed?

If a patient exhibits symptoms consistent with chiari malformation, a doctor will conduct a physical exam to rule out other potential causes of the symptoms. The doctor may also order laboratory tests to look for evidence of other underlying conditions. A neurological exam will test key areas of neurological function, including balance, coordination, cognition, muscle strength, and sensory perception.

If, after conducting initial exams and tests, the doctor suspects that chiari malformation might be the cause of the symptoms, they may order one or more imaging tests that can confirm the presence of the malformation. These imaging tests may include:

  • X-rays
  • Magnetic resonance imaging (MRI)
  • Computerized tomography (CT) scans


How Is Chiari Malformation Treated?

Cases of chiari malformation with no symptoms may not require any treatment at all. Doctors will often recommend that patients undergo regular imaging exams to watch for any changes in the condition of the malformation. Medications may be used to treat symptoms such as headaches or neck pain.

Surgical Treatment

In cases where symptoms are present or damage to central nervous system tissue is possible, surgical interventions may be required. Several different types of surgical procedures are possible depending on the particular characteristics of each case. Commonly used procedures include:

  • Posterior fossa decompression. This surgery involves moving a small area of bone at the base of the skull to give the cerebellum more room. This procedure often relieves pressure and helps with cerebrospinal fluid circulation.
  • Dura mater incision and patch. These procedures involve cutting through the protective tissue that covers the brain and spinal cord. An incision in the dura can help to relieve pressure, and the addition of a flexible patch can allow more room for the cerebellum, brain stem, and/or spinal cord. The patch may be made from tissue from another part of the body or from an artificial material.
  • Electrocautery. This procedure involves the removal of the lower part of the cerebellum (called the cerebellar tonsils). This part of the cerebellum has no known function, and its removal does not cause loss of neurological function. Removal of the cerebellar tonsils gives the rest of the cerebellum more room.

Other surgical procedures may be required if the patient is also suffering from other disorders, such as spina bifida or hydrocephalus.

How Does Chiari Malformation Progress?

Chiari malformation is not always a progressive disorder that gets worse over time, but some cases may eventually lead to symptoms and complications that require treatment. In cases where symptoms are not present at birth or during childhood, symptoms and complications may develop later in life.

Potential complications of chiari malformation include:

  • Hydrocephalus. This is the buildup of cerebrospinal fluid around the brain. The condition can be life-threatening.
  • Syringomyelia. This disorder involves the development of a fluid-filled cyst in the spinal column. The condition can cause severe neurological symptoms.
  • Tethered cord syndrome. In this disorder, the spinal cord becomes fused with the tissues surrounding it. Serious nerve damage can result.
  • Spinal curvature. Chiari malformation, particularly type I, may cause the spine to develop abnormally. Spinal curvature may also be associated with syringomyelia.

How Is Chiari Malformation Prevented?

There is no known way to prevent chiari malformation. However, research has identified some risk factors linked to spina bifida and other neural tube birth defects that are often associated with chiari malformation. Women who are pregnant or who could become pregnant can reduce their risk of having a baby with a neural tube defect by addressing these factors.

  • Ensure an adequate intake of folic acid. The recommended daily dose of folic acid is 400 micrograms (mcg). Women who have had a previous pregnancy with a neural tube defect may be encouraged to take a higher dose. Consult a doctor for guidance.
  • Manage diabetes according to your doctor’s instructions, and have blood-sugar levels under control before you become pregnant.
  • Take steps to control obesity.
  • Avoid hot tubs, saunas, and high-temperature environments during pregnancy. Treat high fevers promptly with the over-the-counter fever reducer acetaminophen.
  • Tell your doctor about any medications or dietary supplements you’re taking.

Chiari Malformation Caregiver Tips

If your child or loved one suffers from chiari malformation, keep these caregiving tips in mind:

  • Learn and educate. Find out all you can about chiari malformation so that you can be an effective advocate for your child. The more you know, the better you’ll be able to make informed decisions about treatment. You’ll also be able to educate teachers and others who will be responsible for supporting your child in the future.
  • Remember the positives. The disorder may be limiting in some ways, but your child will still be capable of living a full, happy life. Concentrate on the possibilities rather than the limitations.
  • Get help when you need it. Find a support group of people who share your experience with chiari malformation. The support of others who know what you’re going through can be invaluable.

Chiari Malformation Brain Science

Scientists are conducting research to help them better understand what causes chiari malformation and other neural tube defects. Their hope is that a better understanding of the origins of the disorders could lead to preventive interventions or more effective treatments. Current areas of research include:

  • Genetics. Scientists have focused their attention on a particular chemical pathway that is important in regulating the body’s cell growth. Certain abnormal gene variations (mutations) that affect this pathway have been linked to cell overgrowth. These mutations may play a role in the development of some cancers, and they may also be connected to brain cell overgrowth that leads to conditions such as chiari malformation. Research in this area is preliminary.
  • Animal studies. Scientists are studying fish embryos in an attempt to better understand the development of a part of the nervous system called the midbrain-hindbrain boundary (MHB). In humans, activity in this area is instrumental in the development of the cerebellum. Understanding how the MHB develops in animals is a first step toward understanding this crucial process in humans.

Chiari Malformation Research

Title: Online Acceptance and Commitment Therapy for Chronic Pain in Sample of People With Chiari Malformation

Stage: Recruiting

Contact: Douglas L Delahanty, PhD

Kent State University

Kent, OH 

Twenty percent of US adults report chronic pain symptoms. Both psychological symptoms and sleep issues commonly co-occur with chronic pain. Chronic pain is a frequently reported symptom of Chiari Malformation (CM); however, the cause of pain symptoms is not fully understood, and pain is not associated with the extent of neural abnormality in CM.

ACT is not a set of techniques, but rather a way of thinking. ACT encourages acceptance, as opposed to avoidance of unwanted feelings, all in the context of mindfulness (i.e., being aware of one’s present environment and in tune with internal thoughts and emotions). ACT has been found to be successful at reducing pain perceptions and targeting multiple symptoms at one time. However, ACT has not been examined in CM and it is unknown whether ACT will improve sleep as well as pain-related symptoms. The purpose of the current study is to assess the efficacy of an online ACT intervention at reducing pain interference and sleep dysfunction symptoms in a sample with CM. It is hypothesized that CM patients may benefit from Acceptance and Commitment Therapy (ACT). More specifically it is hypothesized that the treatment group will report significantly less pain interference and psychological flexibility compared to the control group. It is also hypothesize that ACT will mediate the relationship between sleep dysfunction and pain interference.

Based on power analyses the sample size will be 56. The sample will be recruited online and randomized to the treatment or control group. The intervention will consist of eight modules that are administered weekly over eight weeks. Additionally, a 7-day sleep diary will be administered the week prior to the intervention and the week after the intervention. Follow up assessments will be administered upon completion of the 8-week intervention (at the beginning of week 9), 1-month after, and 3 months after the completion of the intervention.


Title: Analysis of the Chiari I Malformation

Stage: Recruiting

Principal investigator: John D Heiss, MD

National Institute of Neurological Disorders and Stroke (NINDS)

Bethesda, MD

The purpose of this study is to better understand the genetic factors related to the Chiari I malformation. In people with this abnormality, the lower part of the skull is smaller than normal. As a result, the lowest part of the brain, called the cerebellar tonsils, protrudes out of the hole at the bottom of the skull into the spinal canal. This study will try to discover the location of the genes responsible for the malformation.

Candidates for this study are: 1) Patients with Chiari I malformation who also have a family member with the abnormality or a family member with syringomyelia (a cyst in the spinal cord that is often associated with the Chiari I malformation). 2) Family members of patients with the Chiari I malformation.

Participants will have a medical history and physical and neurologic examinations. They will undergo magnetic resonance imaging (MRI) of the brain and cervical (neck) spinal cord to measure the size of the head and determine the presence of the Chiari I malformation and syringomyelia. A small blood sample (about 2 tablespoons) will be drawn for DNA studies relating to the Chiari I malformation.


Title: Fetoscopic Repair of Isolated Fetal Spina Bifida

Stage: Recruiting

Principal Investigator:  Jena Miller, MD  

Johns Hopkins University

Baltimore, MD

The purpose of this investigation is to evaluate maternal and fetal outcomes following fetoscopic repair of fetal spina bifida at the Johns Hopkins Hospital.

The hypothesis of this study is that fetoscopic spina bifida repair is feasible and has the same effectiveness as open repair of fetal spina bifida, but with the benefit of significantly lower maternal and fetal complication rates. The fetal benefit of the procedure will be the prenatal repair of spina bifida. The maternal benefit of fetoscopic spina bifida repair will be the avoidance of a large uterine incision. This type of incision increases the risk of uterine rupture and requires that all future deliveries are by cesarean section. The use of the minimally invasive fetoscopic surgical technique may also lower the risk of preterm premature rupture of membranes and preterm birth compared to open fetal surgery. Finally, successful fetoscopic spina bifida repair also makes vaginal delivery possible.

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