Chiari malformation type 2

Alternate names

Arnold-Chiari malformation; Chiari type II malformation; Chiari malformation type II; Arnold Chiari malformation type II

Definition

Chiari malformation type 2 (CM type II) is a type of Chiari malformation in which both the cerebellum and brain stem tissue extend into the foramen magnum (the hole at the skull base for passing of the spinal cord).

Cause

The exact cause of CM type II is not known but it appears to be due to defects in the brain and spinal cord that occur during fetal development.

Inheritance

• Chiari malformation type 2 usually occurs sporadically (in people with no family history of the condition).
• However, the exact cause is not known.
• Genes may play a role in predisposing a person to the condition, but environmental factors (such as lack of proper vitamins or nutrients in the maternal diet during pregnancy) may also contribute to the condition.
• There have been reports in the medical literature of families in which more than one family member had a Chiari malformation.
• However, limited information specific to familial cases of Chiari malformation type 2 is available.

Signs and symptoms

• Individuals with Type II have symptoms that are generally more severe than in Type 1 and usually appear during childhood.
• This disorder can cause life-threatening complications during infancy or early childhood, and treating it requires surgery.
• In Type II, also called classic CM, both the cerebellum and brain stem tissue protrude into the foramen magnum.
• Also the nerve tissue that connects the two halves of the cerebellum may be missing or only partially formed.
• Type II is usually accompanied by a myelomeningocele—a form of spina bifida that occurs when the spinal canal and backbone do not close before birth. (Spina bifida is a disorder characterized by the incomplete development of the brain, spinal cord, and/or their protective covering.)
• A myelomeningocele usually results in partial or complete paralysis of the area below the spinal opening.
• The term Arnold-Chiari malformation (named after two pioneering researchers) is specific to Type II malformations.

Diagnosis

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

The physician may also order one of the following diagnostic tests:

• Magnetic resonance imaging (MRI) is the imaging procedure most often used to diagnose a Chiari malformation.

It uses radio waves and a powerful magnetic field to painlessly produce either a detailed three-dimensional picture or a two-dimensional “slice” of body structures, including tissues, organs, bones, and nerves.

• X-rays use electromagnetic energy to produce images of bones and certain tissues on film.

An X-ray of the head and neck cannot reveal a CM but can identify bone abnormalities that are often associated with the disorder.

• Computed tomography (CT) uses X-rays and a computer to produce two-dimensional pictures of bone and blood vessels.

CT can identify hydrocephalus and bone abnormalities associated with Chiari malformation.

Treatment

• People with Chiari malformation type II are typically treated with surgery.
• Surgery may include closure of open neural tube defects shortly after birth, treatment for hydrocephalus (most often by use of a shunt), and posterior fossa decompression (creating more space for the cerebellum and relieving pressure on the spinal cord).
• Medical issues may involve management of neurogenic bowel and bladder, neonatal feeding difficulties, respiratory failure, and apnea.
• As with any form of surgery, there are risks associated with surgery to treat Chiari malformations.
• Sometimes, surgery leads to no improvement or even worsening of symptoms.
• For example, if nerve injury in the spinal canal has already occurred, surgery will not reverse the damage.
• However, most people who have surgery have improvement of symptoms afterwards.
• Even if symptoms do not improve significantly, surgery might prevent existing symptoms from worsening.

Prognosis

• The long-term outlook depends on the nature of the malformation and the symptoms present in each person.
• Although some people experience a reduction of symptoms, there is no guarantee that surgery will help every person.
• Nerve damage that has already occurred usually cannot be reversed with surgery, and pain from nerve damage can be difficult to treat.
• Some people may need repeat surgeries.

NIH genetic and rare disease info

• NIH info on Chiari malformation type 2

Chiari malformation type 2 is a rare disease.

Chiari malformation type 2 Resources
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