Chiari malformation is a structural defect in the cerebellum, the part of the brain that controls balance.

What Is Chiari Malformation?

Normally the cerebellum and parts of the brainstem sit in an indented space at the lower rear 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 a chiari malformation (CM).

CMs may develop when the bony space is smaller than normal, causing the cerebellum and brainstem to be pushed downward into the foramen magnum and into the upper spinal canal. The resulting pressure on the cerebellum and brainstem may affect functions controlled by these areas and block the flow of cerebrospinal fluid (CSF) — the clear liquid that surrounds and cushions the brain and spinal cord — to and from the brain.

CMs may be congenital, or present at birth, the result of structural defects in the brain and spinal cord that occur during fetal development. They also may develop 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 four types of CM:

  • CM1, the most common form of CM, involves the extension of the lower part of the cerebellum into the foramen magnum without the involvement of the brainstem. (Normally, only the spinal cord passes through this opening.) CM1 typically appears in adolescence or adulthood and is the only type of CM that can be acquired.
  • CM2 (classic CM or Arnold-Chiari malformation) involves the extension of both cerebellar and brainstem tissue into the foramen magnum. The nerve tissue that connects the two halves of the cerebellum may be partially complete or absent. CM2 is usually accompanied by a myelomeningocele — a form of spina bifida that occurs when the spinal canal and backbone do not close before birth, causing the spinal cord and its protective membrane to protrude through a sac-like opening in the back – which usually results in partial or complete paralysis of the area below the spinal opening.
  • CM3 is characterized by serious neurological defects. The cerebellum and brainstem protrude, or herniate, through the foramen magnum into the spinal cord. Part of the brain’s fourth ventricle, a cavity that connects the upper parts of the brain and circulates CSF, may also protrude through the hole and into the spinal cord. In rare instances, the herniated cerebellar tissue can cause an occipital encephalocele, a pouch-like structure that protrudes out of the back of the head or the neck and contains brain matter. The covering of the brain or spinal cord can also protrude through an abnormal opening in the back or skull.
  • CM4 involves an incomplete or underdeveloped cerebellum — a condition known as cerebellar hypoplasia. In this rare form of CM, the lower cerebellum is located further down the spinal canal, parts of the cerebellum are missing and portions of the skull and spinal cord may be visible.

What Are The Symptoms Of Chiari Malformation?

Patients with CM1 often are asymptomatic and may not know they have the condition. Adolescents and young adults who have CM but no symptoms may, later in life, develop signs of the disorder, which 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, sneezing or straining
  • Hand coordination and fine motor skill impairment

Spinal curvature is common among patients with CM1. Two types that may occur in conjunction with CM include scoliosis – a lateral, or side-to-side, curvature of the spine – or kyphosis, a forward bending of the spine. Spinal curvature is seen most often in children with CM whose skeletons have not fully matured.

Symptoms of any of the above types of CM in infants may include:

  • Difficulty swallowing
  • Irritability during feeding
  • Excessive drooling
  • Weak cry
  • Gagging or vomiting
  • Arm weakness
  • Stiff neck
  • Breathing problems
  • Developmental delays
  • Inability to gain weight.

How Is Chiari Malformation Diagnosed?

To determine whether you have CM, your provider will examine your back and your medical history, and may order an X-ray, bone scan, myelogram, computed tomography (CT) scan and/or magnetic resonance imaging (MRI) to rule out another disorder as the cause of your symptoms.

How Is Chiari Malformation Treated?

Treatment options for CM vary. For those whose CMs are asymptomatic or whose symptoms, such as pain, can be addressed with conservative therapies such as medication, surgery may not be needed. For those whose symptoms are already severe or worsening, surgery may be required to correct the structural/functional defects affecting the spinal cord and halt the progression of damage to the central nervous system.

Surgical procedures for treating CM include:

  • Decompression surgery to create more space for the cerebellum and to relieve pressure on the spinal column, which 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.
  • Spinal laminectomy, which 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 also may 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 CSF.
  • Infants and children with myelomeningocele may require surgery to reposition the spinal cord and close the opening in the back.

The decision to treat CM surgically requires careful consultation between patient and physician. Factors to be considered are the patient’s current neurological condition and the progression of symptoms over a period of time.

Your surgeon will be able to discuss the risks and benefits of surgery with you, and the likely results of operative versus non-operative treatment.