Chiari Malformations

Chiari malformations are classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal.

Type 1 happens when the lower part of the cerebellum (called the cerebellar tonsils) extends into the foramen magnum. Normally, only the spinal cord passes through this opening. Type 1—which may not cause symptoms—is the most common form of CM. It is usually first noticed in adolescence or adulthood, often by accident during an examination for another condition. Adolescents and adults who have CM but no symptoms initially may develop signs of the disorder later in life.

Individuals with type II have symptoms that are generally more severe than in type 1 and usually appear during childhood. This disorder can cause life-threatening complications during infancy or early childhood, and treating it requires surgery. In type II, also called classic CM, both the cerebellum and brain stem tissue protrude into the foramen magnum. Also, the nerve tissue that connects the two halves of the cerebellum may be missing or only partially formed. Type II is usually accompanied by a myelomeningocele— a form of spina bifida that occurs when the spinal canal and backbone do not close before birth. (Spina bifida is a disorder characterized by the incomplete development of the brain, spinal cord and/or their protective covering.) A myelomeningocele usually results in partial or complete paralysis of the area below the spinal opening. The term Arnold-Chiari malformation (named after two pioneering researchers) is specific to type II malformations.

Type III is very rare and the most serious form of Chiari malformation. In type III, some of the cerebellum and the brain stem stick out, or herniate, through an abnormal opening in the back of the skull. This can also include the membranes surrounding the brain or spinal cord. The symptoms of type III appear in infancy and can cause debilitating and life-threatening complications. Babies with type III can have many of the same symptoms as those with type II but can also have additional severe neurological defects such as mental and physical delays, and seizures.

Type IV involves an incomplete or underdeveloped cerebellum (a condition known as cerebellar hypoplasia). In this rare form of CM, the cerebellum is located in its normal position but parts of it are missing, and portions of the skull and spinal cord may be visible.

Chiari malformations (CM) are most often caused by structural defects in the brain and spinal cord that occur during fetal development. This is called primary or congenital CM. The disorder also can be caused later in life if spinal fluid is drained excessively from the spine due to traumatic injury, disease or infection. This is called acquired or secondary CM. Primary CM is much more common than secondary CM.

CMs are classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal.

• CM type I: the most common form—happens when the lower part of the cerebellum (called the cerebellar tonsils) pushes into the foramen magnum. Normally, only the spinal cord passes through this opening. It is usually first noticed in adolescence or adulthood, often by accident during an examination for another condition. Adolescents and adults who have CM but no symptoms initially may develop signs of the disorder later in life.
• CM type II: also called classic CM—involves both the cerebellum and brain stem tissue pushing into the foramen magnum. The nerve tissue that connects the two halves of the cerebellum may be missing or only partially formed. Type II is usually accompanied by a myelomeningocele—a form of spina bifida that occurs when the spinal canal and backbone do not close before birth (see below). A myelomeningocele usually results in partial or complete paralysis of the area below the spinal opening. Symptoms of type II usually appear during childhood and are generally more severe than in type 1. It can cause life-threatening complications during infancy or early childhood, and treating it requires surgery. The term Arnold-Chiari malformation is specific to type II malformations.
• CM type III: the most serious form—has some of the cerebellum and the brain stem stick out, or herniate, through an abnormal opening in the back of the skull. This can also include the membranes surrounding the brain or spinal cord. Symptoms of this very rare form of CM appear in infancy and can cause debilitating and life-threatening complications. Babies with type III can have many of the same symptoms as those with type II but can also have additional severe neurological defects such as seizures and mental and physical delays.
• CM type IV involves an incomplete or underdeveloped cerebellum (a condition known as cerebellar hypoplasia). In this rare form of CM, the cerebellum is in its normal position but parts of it are missing, and portions of the skull and spinal cord may be visible.

What other conditions are associated with CMs?

• Hydrocephalus is an excessive buildup of cerebrospinal fluid (CSF) in the brain. A CM can block the normal flow of this fluid and cause pressure within the head that can result in mental impairment and/or an enlarged or misshapen skull. Severe hydrocephalus, if left untreated, can be fatal. Hydrocephalus can occur with any type of CM but is most commonly associated with type II.
• Spina bifida is the incomplete closing of the backbone and membranes around the spinal cord. Individuals with CM type II usually have myelomeningocele, and a baby’s spinal cord remains open in one area of the back and lower spine. The membranes and spinal cord protrude through the opening in the spine, creating a sac on the baby’s back. This can cause neurological impairments such as muscle weakness, paralysis and scoliosis.
• Syringomyelia is a disorder in which a CSF-filled tubular cyst called a syrinx forms within the spinal cord’s central canal. The growing syrinx destroys the center of the spinal cord and presses on the nerves, resulting in pain, weakness and stiffness. You may lose the ability to feel extremes of hot or cold, especially in your hands.
• Tethered cord syndrome occurs when a child’s spinal cord abnormally attaches to the tissues around the bottom of the spine—preventing the spinal cord from moving freely within the spinal canal. As a child grows, the disorder worsens and can result in permanent damage to the nerves that control the muscles in the lower body and legs. Children who have a myelomeningocele have an increased risk of developing a tethered cord later in life.
• Spinal curvature is common among individuals with syringomyelia or CM Type I. The spine either may bend to the left or right (scoliosis) or may bend forward (kyphosis).

In the past, it was estimated that the condition occurs in about one in every 1,000 births. However, the increased use of diagnostic imaging has shown that Chiari malformation may be much more common. Complicating this estimation is the fact that some children who are born with this condition may never develop symptoms or show symptoms only in adolescence or adulthood. Chiari malformations occur more often in women than in men, and type II malformations are more prevalent in certain groups, including people of Celtic descent. 

Individuals with CM often have these related conditions: 

• Hydrocephalus is an excessive buildup of CSF in the brain. A CM can block the normal flow of this fluid and cause pressure within the head that can result in mental defects and/or an enlarged or misshapen skull. Severe hydrocephalus, if left untreated, can be fatal. The disorder can occur with any type of Chiari malformation, but is most commonly associated with type II. 
• Spina bifida is the incomplete closing of the backbone and membranes around the spinal cord. In babies with spina bifida, the bones around the spinal cord do not form properly, causing defects in the lower spine. While most children with this birth defect have such a mild form that they have no neurological problems, individuals with type II Chiari malformation usually have myelomeningocele, and a baby’s spinal cord remains open in one area of the back and lower spine. The membranes and spinal cord protrude through the opening in the spine, creating a sac on the baby’s back. This can cause a number of neurological impairments, such as muscle weakness, paralysis and scoliosis. 
• Syringomyelia is a disorder in which a CSF-filled tubular cyst, or syrinx, forms within the spinal cord’s central canal. The growing syrinx destroys the center of the spinal cord, resulting in pain, weakness and stiffness in the back, shoulders, arms or legs. Other symptoms may include a loss of the ability to feel extremes of hot or cold, especially in the hands. Some individuals also have severe arm and neck pain. 
• Tethered cord syndrome occurs when a child’s spinal cord abnormally attaches to the tissues around the bottom of the spine. This means the spinal cord cannot move freely within the spinal canal. As a child grows, the disorder worsens, and can result in permanent damage to the nerves that control the muscles in the lower body and legs. Children who have a myelomeningocele have an increased risk of developing a tethered cord later in life. 
• Spinal curvature is common among individuals with syringomyelia or CM type I. The spine either may bend to the left or right (scoliosis) or may bend forward (kyphosis).

Because Chiari malformations (CM) are most often caused by structural defects in the brain and spinal cord that occur during fetal development, they cannot be prevented. If a CM is suspected, an MRI is performed to create three-dimensional images of the brain and upper spinal cord for review.

Some people with Chiari malformations do not show symptoms. Symptoms may change for some individuals, depending on the compression of the tissue and nerves and on the buildup of cerebrospinal fluid (CSF) pressure. If you have a CM, your symptoms may include:

• Headache, especially after sudden coughing, sneezing or straining
• Neck pain
• Hearing or balance problems
• Muscle weakness or numbness
• Dizziness
• Difficulty swallowing or speaking
• Vomiting
• Ringing or buzzing in the ears (tinnitus)
• Curvature of the spine (scoliosis)
• Insomnia
• Depression
• Problems with hand coordination and fine motor skills
• Difficulty swallowing
• Excessive drooling, gagging or vomiting
• Breathing problems
• Difficulty eating and an inability to gain weight

Currently, no test is available to determine if a baby will be born with a Chiari malformation. Since Chiari malformations are associated with certain birth defects like spina bifida, children born with those defects are often tested for malformations. However, some malformations can be seen on ultrasound images before birth. 

Many people with Chiari malformations have no symptoms and their malformations are discovered only during the course of diagnosis or treatment for another disorder. The doctor will perform a physical exam and check the person’s memory, cognition, balance (functions controlled by the cerebellum), touch, reflexes, sensation and motor skills (functions controlled by the spinal cord). The physician may also order one of the following diagnostic tests: 

• Magnetic resonance imaging (MRI) is the imaging procedure most often used to diagnose a Chiari malformation. It uses radio waves and a powerful magnetic field to painlessly produce either a detailed three dimensional picture or a two-dimensional “slice” of body structures, including tissues, organs, bones and nerves.
• X-rays use electromagnetic energy to produce images of bones and certain tissues on film. An X-ray of the head and neck cannot reveal a CM but can identify bone abnormalities that are often associated with the disorder. 
• Computed tomography (CT) uses X-rays and a computer to produce two-dimensional pictures of bone and blood vessels. CT can identify hydrocephalus and bone abnormalities associated with Chiari malformation.

Treatment for Chiari malformations depends on your symptoms and their severity. Talk with your doctor about your symptoms and how they affect you, as well as what treatments you may need. CMs that do not show symptoms and do not interfere with your activities of daily living may only need regular monitoring by a physician with diagnostic imaging. Medications may be prescribed to ease headache and pain.

In many cases, surgery is the only treatment available to ease symptoms or halt the progression of damage to the central nervous system. Surgery can improve or stabilize symptoms in most individuals. More than one surgery may be needed to treat the condition.

The most common surgery to treat CM is posterior fossa decompression, which creates more space for the cerebellum and reduces pressure on the spinal cord and restores the normal flow of cerebrospinal fluid (CSF). It involves making an incision at the back of the head and removing a small portion of the bone at the bottom of the skull (a procedure called a craniectomy). In some cases, the arched, bony roof of the spinal canal, called the lamina, may also be removed (spinal laminectomy).

In some instances, the surgeon may use a procedure called electrocautery to remove the cerebellar tonsils, allowing for more free space. These tonsils do not have a recognized function and can be removed without causing any known neurological problems.

The severity of Chiari malformations can vary from person to person, but generally CMs are not considered life-threatening. Some people experience painful headaches, movement problems and other unpleasant symptoms that can be treated with prescribed pain medication, but many people will not have any symptoms.

To further your understanding of your diagnosis and to contribute to cutting-edge research, consider participating in a clinical trial so clinicians and scientists can learn more about causes, symptoms, treatment and prevention. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research, visit NIH Clinical Research Trials and You. Learn about clinical trials currently looking for participants at Clinicaltrials.gov.