Chiari I Malformation

What is a Chiari I Malformation?

Chiari I malformation is an anomaly that is unassociated with other congenital brain malformations.  The lowest part of the cerebellum, called the "tonsils" of the cerebellar, is displaced downward through the foramen magnum (the opening at the bottom of the skull) into the upper cervical spinal canal.  It is believed that the posterior bony skull fossa is relatively too small for the cerebellum, resulting in it's downward displacement into the cervical spine.

Normal

Chiari Type I

The image on the left is a normal patient.  The one on the right has Chiari Type I malformation.  The blue arrow is pointing to the cerebellum that is herniating down into the spinal canal.

Who gets Chiari I Malformations?

The average age at presentation is 41 years.  Females slightly outnumber males.  It is seen in adolescents but occasionally is first encountered in older individuals.  Rarely, it is seen in several members of one family.

What are the symptoms of Chiari I Malformation?

The most common symptom is pain, especially headache that is usually felt in the back of the head, and is aggravated by coughing and straining.  Weakness is also prominent, especially in the hands.  Other symptoms include the following:

• Pain: headache, neck pain, arm pain, leg pain
• Weakness
• Numbness
• Loss of temperature sensation
• Unsteadiness
• Double vision
• Slurred speech
• Trouble swallowing
• Vomiting
• Ringing in the ears (tinnitus)

How are Chiari I Malformations evaluated?

MRI: this is the diagnostic test of choice, and easily shows the herniation of the cerbellar tonsils.

What other anomalies is Chiari I Malformation associated with?

Chiari I malformation is usually not associated with other brain anomalies.  However, spinal cord, skull base, and spine problems are common in this disorder.

Spinal cord: Accumulation of cerebrospinal fluid (CSF) within the spinal cord is a frequent finding in patients with Chiari I.  A cyst, called a "syrinx", can form.  This can cause serious injury to the cord.  A syrinx is present in 20-40% of all patients with Chiari I.

Skull base and spine: Bony anomalies of the base of the skull are seen in about one quarter of all patients with Chiari I malformation.

How is Chiari I Malformation treated?

Surgical treatment is the treatment of choice for symptomatic Chiari I malformation.  Prior to treatment it must be clearly established that the Chiari malformation is the cause of the symptoms.  Once this is determined the operative treatment consists of a suboccipital decompression.  This operation essentially involves removing bone in the region of the tonsillar herniation (suboccipital) along with the posterior margin of the foramen magnum and usually the posterior ring of the C1 vertebrae.  Once the bone is removed the dura mater (covering over the spinal cord and brain) is opened.

The dura mater is then closed with a dural patch graft placed so as to increase the space available.  The main benefit of the surgical therapy is to arrest the progression of symptoms.  Severe complications following this treatment are rare.  In patients with syringomyelia, the spinal cord cyst generally becomes smaller following suboccipital decompression.