Chiari Malformation
Chiari Malformation
What it is, how it's diagnosed, and the treatment options available today.
What Is Chiari Malformation?
The Chiari malformation (CM) is an abnormality in the lower part of the brain called the cerebellum. There are several different forms. The most common type is the Chiari I malformation (CMI). Less commonly, it may be known as Arnold-Chiari malformation, tonsillar herniation, or tonsillar ectopia. Most cases of Chiari are congenital, meaning they are present from birth, though many people are not diagnosed until adolescence or adulthood.
In normal anatomy, the cerebellar tonsils are located just above the foramen magnum — the opening at the base of the skull. In an individual with CM, the cerebellar tonsils hang below that line (herniate) into the spinal canal. The degree to which the tonsils extend can vary tremendously.
Types of Chiari Malformation
Chiari 0
Little or no cerebellar tonsillar descent below the foramen magnum. Significant crowding at the craniocervical junction may still block or alter CSF flow, and it may be associated with a syrinx or dilated central canal.
Chiari 1
Defined by radiologists as descent of the cerebellar tonsils 5 mm or more below the foramen magnum. This is the most common form of CM.
Chiari 2
More brain tissue — including parts of the cerebellum and brainstem — extends down into the spinal canal through the normal opening at the base of the skull.
Chiari 3
A rare and severe form of CM in which the cerebellum and brainstem extend through an abnormal opening in the back of the skull.
Chiari 4
An extremely rare condition involving a severely underdeveloped cerebellum, typically fatal during infancy.
Chiari Symptoms
Symptoms of Chiari I malformation can vary widely from person to person. They may develop slowly and gradually over several years, and some people experience symptoms for years before receiving a diagnosis. Because many Chiari symptoms can also occur with other conditions, recognizing the overall pattern of symptoms can be an important part of the diagnostic process.
Headaches and Neck Pain
The most common symptom of Chiari malformation (CM) is a headache, which begins at the back of the head (neck) and radiates upward. The pain is often made worse by, or brought on by, coughing, sneezing, or straining — activities known as Valsalva maneuvers.
Balance, Dizziness & Coordination
- Dizziness or vertigo, especially during a headache or when changing positions
- Poor balance or difficulty walking
- Problems with coordination or gait
Vision & Eye Symptoms
- Blurred or double vision
- Light sensitivity or visual disturbances
- Nystagmus or involuntary eye movements
Numbness, Weakness & Pain
Chiari and related conditions may cause:
- Numbness or tingling in the face, arms, or legs
- Weakness, sometimes affecting one side more than the other
- Pain in the head, neck, back, or limbs
- Difficulty with coordination
CM can also cause a syrinx — a fluid-filled cavity within the spinal cord — which can contribute to neurological symptoms in the arms, legs, or other areas.
Swallowing & Other Neurological Symptoms
Compression or dysfunction involving the brainstem and cranial nerves may cause:
- Difficulty swallowing or choking
- Hoarseness or changes in speech
- Facial tingling or numbness
- Fainting (syncope) or episodes of altered consciousness
- Sleep apnea or other breathing problems
Other Symptoms
People with Chiari may also report symptoms that affect their overall well-being and daily functioning, including:
- Fatigue
- Sleep difficulties
- Nausea or vomiting
- Difficulty concentrating or remembering
- "Brain fog"
- Changes in heart rate or blood pressure (tachycardia, POTS)
Symptoms vary and do not always correspond directly to the amount of tonsillar descent seen on an MRI.
Chiari Testing & Treatment
Chiari Evaluation
Chiari I malformation is usually identified through magnetic resonance imaging (MRI). MRI can show the position of the cerebellar tonsils, the amount of space at the base of the skull, and whether there is a syrinx or other abnormalities involving the brain or spinal cord.
Additional testing may include:
- MRI of the brain and spine to evaluate the brain, craniocervical junction, and spinal cord
- Cine MRI (CSF flow study) to evaluate how cerebrospinal fluid (CSF) moves around the brain and spinal cord
- Neurological examination to assess strength, sensation, reflexes, balance, coordination, and other neurological function
- Additional testing when needed to evaluate other conditions that may cause similar symptoms
Getting Started
The first step after diagnosis is to consult with a neurosurgeon who has experience treating and managing this disorder. You may need to travel to find a specialist, and getting a second opinion can be helpful when considering treatment options. A neurologist may also be involved to evaluate symptoms and rule out other neurological conditions.
Nonsurgical Treatment
If symptoms are mild and not progressing, your doctor may recommend monitoring and conservative management. Depending on your symptoms, this may include:
- Medications to manage pain or other symptoms
- Physical therapy
- Activity modification
- Evaluation by a chronic pain specialist
- Regular follow-up and imaging when appropriate
Treatment for CMI depends on a person's symptoms, their severity, and whether symptoms are changing over time. It is estimated that roughly 30% of CMI patients require surgical intervention.
Related Talks
- Decision Tree for Chiari Malformation TreatmentErol Veznedaroglu, MD
- CM/SM: Is Surgery the Only Option?Paramita Das, MD
Chiari Surgery
When symptoms are significant, worsening, or related to complications such as a syrinx, surgery may be recommended. The most common surgery for Chiari I is called posterior fossa decompression.
The goal of decompression surgery is to create more space at the base of the skull and upper spine, reduce crowding, and improve the flow of cerebrospinal fluid (CSF).
During surgery, the surgeon removes a small portion of bone from the back of the skull and, in some cases, the upper cervical vertebra. Some surgeons also open the dura, the protective covering around the brain and spinal cord, and may place a patch to create additional space. Specific surgical techniques will vary among surgeons, and there is not yet a consensus on which specific approach is best for every patient.
Understanding the Risks and Benefits
As with any surgery, Chiari decompression has potential risks. These may include CSF leakage or pseudomeningocele, infection or meningitis, nerve or neurological injury, bleeding, and other complications associated with major surgery.
The decision to have surgery should take into account your symptoms, quality of life, potential benefits, and possible risks. Ask your specialist questions until you understand the recommended procedure and feel comfortable making an informed decision. During an ASAP annual conference, Dr. John Heiss explains what to expect after Chiari surgery.
Learn More From the ASAP Medical Advisory Board
- Chiari Malformation Decompression SurgeryGerald Grant, MD
- New Surgical Technique for Chiari Malformation DecompressionErol Veznedaroglu, MD
- Surgical Management of the Complex Chiari MalformationDeb Bhowmick, MD
- Surgical Failure in Chiari Malformation – What to Do NextBrian Dlouhy, MD
- Don't Touch my Tonsils! (Tonsillectomy)Robert Keating, MD
- Counterpoint: Take Out My Tonsils! (Tonsillectomy)Paolo Bolognese, MD
- Enhancing Recovery Following Chiari SurgeryJohn Oro, MD
Is Chiari Malformation Hereditary?
Research suggests that Chiari malformation may have a hereditary component, though it is not considered a strictly genetic disorder. There appears to be a possible inherited susceptibility; however, no single gene mutation has been identified that fully explains the condition.
Research suggests that both genetic and structural traits may contribute to Chiari malformation. Investigators have found strong overlap between Chiari and several connective-tissue and craniofacial syndromes. Learn more about Chiari and genetics.
MRI scanning is recommended for family members who have signs or symptoms of the disorder.
