A Chiari malformation occurs when parts of the brain protrude through an opening in the base of the skull (foramen magnum) that normally only contains the spinal cord. In most kinds of Chiari malformation, the cerebellum (controls motion and balance) pushes through the opening in the skull that connects to the spinal canal. The brain stem also can be affected. These structural abnormalities put pressure on the cerebellum and brain stem, and this can block the normal flow of cerebral spinal fluid, which cushions the brain and spinal cord.
The exact cause of Chiari malformations is unknown. Theories suggest that exposure to toxins (such as hazardous substances, drugs or alcohol) or poor nutrition during fetal development may play a role.
Chiari malformations are present in approximately 1 in 1,000 people. The condition is classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal. There are four types of Chiari malformation:
- Type I. Type I is the most common form of Chiari malformation. A type I Chiari malformation only involves parts of the cerebellum pushing outside of the skull. Many people with this form of Chiari malformation have no symptoms. The condition often is discovered by coincidence, usually during a test for another condition. It is most often diagnosed in adolescence and adulthood. Between 30 and 50 percent of patients with type I Chiari malformations also have abnormalities at the base of the skull and spine. This includes compression of the spine into the skull, bony unions of the cervical vertebrae, cervical spina bifida and scoliosis.
- Type II. Type II Chiari malformation is associated with spina bifida. In type II Chiari malformations, parts of the cerebellum and brain stem extend into the foramen magnum. This condition occurs with myelomeningocele, a form of spina bifida where the spinal canal and backbone do not properly close before birth. When this happens, the spinal cord protrudes through the back in a sac-like opening. A myelomeningocele can cause partial or complete paralysis of the area below the spinal opening. Hydrocephalus (buildup of cerebrospinal fluid in the brain) also may be associated with type II Chiari malformations and myelomeningocele.
- Type III. Type III Chiari malformation is the most severe form. It occurs infrequently. The cerebellum, brain stem and parts of the fourth ventricle (a structure that contains cerebrospinal fluid) herniate (push out) through the foramen magnum and compress the spinal cord. This can be accompanied by an occipital encephalocele (large sac that contains brain tissue and protrudes from the back of the skull and neck). This type of Chiari malformation is associated with severe neurological deficits.
- Type IV. Type IV Chiari malformation occurs when the cerebellum is not completely developed (hypoplastia). Portions of the skull may be missing.
Many adults and children with Chiari malformations have no symptoms at all. Symptoms can vary by age group and be present alone or in combination.
Infants with any form of Chiari malformation may show these symptoms:
- Arching of the back
- Feeding problems
- Swallowing problems (choking and gagging)
- Aspiration of food into the lungs
- Gastroesophageal reflux
- Breathing problems
- Stiff neck
- Arm weakness
- Developmental delay
- Inability to gain weight
Symptoms of type I Chiari malformation include:
- Severe head and neck pain
- Headache pain at the base of the skull
- Collapsing from muscle weakness
- Balance problems
- Blurred or double vision
- Sensitivity to bright lights
Symptoms of type II Chiari malformation include:
- Altered breathing
- Central sleep apnea
- Depressed gag reflex
- Involuntary rapid downward eye movements
- Loss of arm strength
Type III and type IV Chiari malformation is rare, and children who are born with these types often do not survive. Symptoms of type III and type IV Chiari malformation include:
- Severe neurological deficits
- Other severe birth defects
Chiari malformations may be associated with syringomyelia and hydromyelia. These disorders involve a buildup of cerebrospinal fluid that forms a cyst or cavity in the spinal cord. As the cyst (syrinx) grows, it can cause additional symptoms, including:
- Loss of pain sensations in the upper torso and arms
- Loss of hot and cold sensations
- Loss of muscle strength in the hands and arms
Diagnosis of Chiari malformation
If your child shows signs of a Chiari malformation, a neurosurgeon will evaluate him or her to make an accurate diagnosis.
Specialists with Riley at IU Health perform the following exams and tests to diagnose Chiari malformations:
- Computed tomography (CT) scan. This is an X-ray scan that combines cross-sectional images to create highly detailed pictures of the structures of the brain and spinal cord.
- Magnetic resonance imaging (MRI). MRI combines radio waves and a magnetic field to create computer images of the brain and spinal cord.
- X-ray. Electromagnetic energy is used to create images of the head and neck. This can show bone abnormalities in the skull and spine.
If diagnostic tests show that a Chiari malformation is present, a neurosurgeon will discuss with you the best treatment options for your child.
If no symptoms are present with a Chiari malformation, no treatment is needed. Your child’s neurosurgeon will simply monitor your child over time.
Treatment options include:
- Surgery. If symptoms are severe, surgery is the only treatment to relieve pressure on parts of the brain and spinal cord and restore the normal flow of cerebrospinal fluid. Surgery also may be used to reduce excess fluid in cases of hydrocephalus or to drain a syrinx or hydromyelia.
The type of procedure performed depends on the specific type of Chiari malformation and symptoms:
- Shunt placement. In rare circumstances, a shunt can be surgically placed to relieve pressure in the head caused by hydrocephalus or to drain fluid from a syrinx or hydromyelia. A shunt drains fluid through a small flexible tube. The tube carries the excess fluid to the abdomen or atria of the heart where it is absorbed by the body.
- Decompression surgery. This procedure involves removing the back of the foramen magnum to provide more space for the protruding brain structures. The back of the first few cervical vertebrae also may be removed.
- Orthopedic surgery evaluation. If a syrinx or scoliosis is present, your child’s doctor may also recommend evaluation by an orthopedic surgeon to determine if treatment can improve those specific symptomatic conditions.
Your child’s neurosurgeon will discuss the benefits of surgery with you. While many patients see a reduction in symptoms, it is possible that surgery may not bring relief for every patient.
Key Points to Remember
Key Points to Remember
- A Chiari malformation occurs when parts of the brain protrude through an opening in the base of the skull (foramen magnum) that normally only contains the spinal cord.
- There are four types of Chiari malformation.
- Doctors use imaging tests to diagnose Chiari malformations.
- Surgery is the only treatment for Chiari malformations that cause severe symptoms. Asymptomatic Chiari malformations require no treatment.
Support Services & Resources
Support Services & Resources
View these links to discover support groups and more resources for Chiari malformations.
Riley at IU Health offers a broad range of supportive services to make life better for families who choose us for their children's care.
This national group provides patient information about Chiari malformation.
The National Institutes of Health provide more information about the symptoms, treatment and research related to Chiari malformation.
Chiari Malformation Research
Chiari Malformation Research
The neurosurgery team at Riley at IU Health participates in research to find the best treatments for Chiari malformations and syringomyelia. We take part in the Park-Reeves Syringomyelia Research Consortium, a multicenter research effort that focuses on treatments for type I Chiari malformations.
Our neurosurgeons also actively work on the National Spina Bifida Patient Registry,
which is managed by the Centers for Disease Control and Prevention. This multicenter study evaluates the decision-making process and management of patients with myelomeningocele.
In addition to our primary hospital location at the Academic Health Center in Indianapolis, IN, we have convenient locations to better serve our communities throughout the state.