Chiari Malformation Type 1

Chiari malformation type 1 (CM1) is a congenital anomaly of the cerebellum — the part of brain located at the base of the skull and brain stem. In CM1, the tissue in the lower part of the cerebellum protrudes into the spinal canal, which can obstruct cerebrospinal fluid from flowing into the spinal canal. This causes pressure on surrounding tissues. The cerebellum is important for movement and balance, and the brain stem is important for basic body functions. The malformation can be mild with few to no symptoms, or it can be severe.

Signs & Symptoms

Symptoms may vary depending on the severity of your CM. The most common symptom is a severe headache in the back of the head. The headache:

  • May come and go
  • Radiate to your neck and shoulders
  • Worsen when you cough, sneeze, or strain

Other symptoms include:

  • Loss of coordination
  • Difficulty swallowing or speaking
  • Muscle weakness
  • Trouble sleeping
  • Ringing in the ears or hearing problems
  • Dizziness
  • Fatigue
  • Vision problems
  • Numbing or tingling in extremities

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Causes & Risks

While the cause of Chiari malformation in children and adults is unknown, it is thought to begin in the early stages of brainstem and spinal cord development (congenital). Symptoms for Chiari malformation may also develop later in life (secondary CM). These cases may be caused by a leak of cerebrospinal fluid (CSF) around the brain and spinal cord, leading to low pressure.

In children, CM occurs equally in boys and girls. In adults, it is three times more common in women than men. Family history also increases the risk of CM.

Chiari malformation is evaluated with a medical history and physical exam along with imaging tests such as MRI and/or CT scan.

Treatment for Chiari malformation depends on the severity of symptoms. Treatment may include:

  • Medicine or alternative treatment to relieve head and neck pain
  • Decompression surgery to prevent the worsening of malformation, or to treat severe symptoms

If you are not experiencing any symptoms, you may not need treatment.