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Chiari Malformation

Chiari malformations (CM) are structural defects in the cerebellum, the part of the brain that controls balance. When the indented bony space at the lower rear of the skull is smaller than normal, the cerebellum and brainstem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid (the liquid that surrounds and protects the brain and spinal cord).

There are three primary types of CM. The most common is Type I, which may not cause symptoms and is often found accidently during an examination for another condition.

Type II, also called Arnold-Chiari malformation, is usually accompanied by myelomeningocele – a form of spina bifida that occurs when the spinal canal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening.

Type III, the most serious form of CM, causes severe neurological defects.

Individuals who have a Chiari malformation often have these related conditions:

Hydrocephalus is an excessive buildup of cerebrospinal fluid (CSF) in the brain. A CM can block the normal flow of fluid, resulting in pressure within the head that can cause 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 CM, but is most commonly associated with Type II.

Syringomyelia, or hydromyelia, is a disorder in which a cerebrospinal fluid-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 headaches and 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 the spinal cord attaches itself to the bony spine. This progressive disorder causes abnormal stretching of the spinal cord and can result in permanent damage to the muscles and nerves 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. Two types of spinal curvature can occur in conjunction with CMs: scoliosis, a bending of the spine to the left or right, and kyphosis, a forward bending of the spine. Spinal curvature is seen most often in children with CM, whose skeleton has not fully matured.

CMs may also be associated with certain hereditary syndromes that affect neurological and skeletal abnormalities, other disorders that affect bone formation and growth, fusion of segments of the bones in the neck and extra folds in the brain.

Common Symptoms

  • Dizziness
  • Muscle weakness
  • Numbness
  • Vision problems
  • Headache
  • Problems with balance and coordination
  • Neck pain
  • Difficulty swallowing
  • Ringing or buzzing in the ears, or hearing loss
  • Insomnia and depression


Symptoms may change for some individuals, depending on the buildup of cerebrospinal fluid and resulting pressure on the tissues and nerves. People with Type 1 CM may not have symptoms. Adolescents and adults who have CM but no symptoms initially may, later in life, develop signs of the disorder. Infants may have symptoms from any type of CM and may have difficulty swallowing, irritability when being fed, excessive drooling, a weak cry, gagging or vomiting, arm weakness, a stiff neck, breathing problems, developmental delays and an inability to gain weight.

Diagnosis

Many people with CM have no symptoms and their malformations are discovered only during the course of diagnosis or treatment for another disorder. Your doctor will perform a physical exam and check your memory, cognition, balance (a function controlled by the cerebellum), touch, reflexes, sensation and motor skills (functions controlled by the spinal cord).

Your doctor may also order one of the following diagnostic tests:

  • X-ray
  • CT scan
  • MRI


Treatment

While medications may ease certain symptoms, such as pain, surgery is the only treatment available to correct functional disturbances or halt the progression of damage to the central nervous system. Most individuals who have surgery see a reduction in their symptoms and/or prolonged periods of relative stability. More than one surgery may be needed to treat the condition.

Posterior fossa decompression surgery is performed on adults with CM to create more space for the cerebellum and to relieve pressure on the spinal column. Surgery involves making an incision at the back of the head and removing a small portion of the bottom of the skull (and sometimes part of the spinal column) to correct the irregular bony structure. Your neurosurgeon may use a procedure called electrocautery to shrink the cerebellar tonsils. This surgical technique involves destroying tissue with high-frequency electrical currents.

A related procedure, called a spinal laminectomy, involves the surgical removal of part of the arched, bony roof of the spinal canal (the lamina) to increase the size of the spinal canal and relieve pressure on the spinal cord and nerve roots.

The surgeon may also make an incision in the dura (the covering of the brain) to examine the brain and spinal cord. Additional tissue may be added to the dura to create more space for the flow of cerebrospinal fluid.

Infants and children with myelomeningocele may require surgery to reposition the spinal cord and close the opening in the back.

Hydrocephalus may be treated with a shunt system that drains excess fluid and relieves pressure inside the head. A sturdy tube that is surgically inserted into the head is connected to a flexible tube that is placed under the skin, where it can drain the excess fluid into either the chest wall or the abdomen so it can be absorbed by the body. An alternative surgical treatment to relieve hydrocephalus is third ventriculostomy, a procedure that improves the flow of cerebrospinal fluid.

A small perforation is made in the floor of the third ventricle and the cerebrospinal fluid is diverted into the subarachnoid space to relieve pressure.

Source: National Institute for Neurological Disorders and Stroke

For More Information

American Association of Neurological Surgeons

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