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What is a Chiari malformation?

A Chiari malformation (CM) is a structural defect in the cerebellum which is the part of the brain that controls the balance. The cerebellum and parts of the brain stem normally sit in an indented space at the lower end of the skull, above the foramen magnum, a funnel-like opening to the spinal canal. When part of the cerebellum is located below the foramen magnum, it is called al Chiari malformation; this develops when the bony space is smaller than normal, causing the cerebellum and brain stem to be pushed downward into the foramen magnum and into the upper spinal canal. This pressure on the cerebellum and the brain stem can affect functions controlled by these areas and block the flow of cerebrospinal fluid (CSF), a clear liquid that surrounds and cushions the brain and spinal cord, to and from the brain.


What causes a Chiari malformation?

There following are causes of Chiari malformations:

  • Primary or congenital Chiari malformation – is caused by structural defects in the brain and spinal cord that occur during fetal development, either by genetic mutations or lack of proper vitamins or nutrients in the maternal diet; this cause is much more common. 
  • Acquired or secondary Chiari malformation – is caused later in life if spinal fluid is drained excessively from the lumbar or thoracic areas of the spine either due to injury, exposure to harmful substances or infection.

There are also four classifications of Chiari malformations. They are classified by the severity of the disorder and the parts of the brain that protrude into the spinal cord.

  • Type I involves the extension of the cerebellar tonsils which is the lower part of the cerebellum into the foramen magnum, without involving the brain stem; Normally, the spinal cord only passes through this opening. Type I is the only type of CM that can be acquired and may not cause symptoms; it is the most common form of CM and usually first noticed in adolescence or adulthood, usually be an accident during an exam for another condition.
  • Type II, also known as classic CM, involves the extension of both cerebellar and brain stem tissue into the foramen magnum and the cerebellar vermis, the nerve that connects the two halves of the cerebellum, may only be partially complete or absent. Type II is usually accompanied by a form a spina bifida that occurs when the spinal canal and backbone do not close before birth, called myelomeningocele. This causes the spinal cord and its protective membrane to protrude through a sac-like opening in the back. A myelomeningocele usually results in partial or complete paralysis of the area below the spinal opening. 
  • Type III involves the cerebellum and brain stem protruding or herniating through the foramen magnum into the spinal cord. Part of the brain's fourth ventricle, a cavity that connects with the upper parts of the brain and circulates CSF, may also protrude through the hole and into the spinal cord. Type III causes severe neurological defects and is the most serious form. 
  • Type IV is rare and involves an incomplete or underdeveloped cerebellum which is a condition known as cerebellar hypoplasia. The cerebellar tonsils are located in a normal position but parts of the cerebellum are missing, and portions of the skull and spinal cord may be visible.


What are the symptoms of Chiari malformation?

Symptoms of CM can include:

  • Neck pain
  • Balance problems
  • Muscle weakness
  • Numbness or other abnormal feelings in the arms or legs
  • Dizziness
  • Vision problems
  • Difficulty swallowing
  • Ringing or buzzing in the ears
  • Hearing loss
  • Vomiting
  • Insomnia
  • Depression
  • Headache made worse by coughing or straining
  • Hand coordination and fine motor skills may be affected

Symptoms may be different or may change for patients, depending on the buildup of CSF and resulting in pressure on the tissues and nerves. Patients with Type I CM may not have symptoms. Adolescents and adults who have CM but show no symptoms at first, may develop signs of the disorder later in life.


How are Chiari malformations diagnosed?

Many patients who have CM usually have no symptoms and their malformations are discovered for the diagnosis or treatments of another disorder. Your physician will perform a physical exam and check your memory, cognition, balance, touch, reflexes, sensation and motor skills. One of the following diagnostic tests may be done as well:

  • X-Ray; this is a fast and painless medical test that helps physicians diagnose and treat medical conditions. X-ray involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the older and most frequently used form of medical imaging. 
  • CT (computed tomography); also known as a CAT scan, uses special x-ray equipment to obtain image data from different angles around the body and then uses computer processing of the information to show 3-D images and cross-sectional images of body tissues and organs.
  • MRI (magnetic resonance imaging); is the imaging procedure most often used to diagnose Chiari malformations. An MRI uses radio waves and a powerful magnetic field to produce a detailed 3-D or 2-D images of the body tissues and organs.


How are Chiari malformations treated?

Some Chiari malformations are asymptomatic and do not interfere with daily activities. In other cases, medications may be taken to ease certain symptoms. Surgery is the only treatment available to correct functional disturbances or stop the progression of damage to the center nervous system. Most patients who have surgery see a reduction in their symptoms and/or prolonged periods of relative stability. 

Please talk to your physician or schedule a consultation at Baylor Scott & White Neurosurgery Associates ​to determine what approach is best for you.