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Different Types of Chiari Malformations

What are Chiari malformations?

Chiari malformations are defects in the cerebellum and the brainstem that cause increase in pressure in the back of the brain producing symptoms.  Normally, the brainstem and cerebellum sit above the opening at the base of the skull called the foramen magnum.  In Chiari malformations, a part of the cerebellum is located below this opening.  The resulting pressure on the brainstem and cerebellum can block the flow of cerebrospinal fluid, clear liquid that surrounds the brain, producing symptoms.

What causes Chiari malformations?

The Chiari malformations can develop for many different reasons.  It can be developmental, meaning that there are structural defects in the development of the cerebellum, spinal cord, and brainstem.  It can also be because of excessive drainage of fluid from the lumbar spine or increased pressure in the brain.

How many types of Chiari malformations are there?

There are 4 types of Chiari malformations. Chiari Type I is the most common and in this type the cerebellar tonsils, which is the lowest part of the cerebellum, is found below the foramen magnum.  Normally, only the spinal cord passes through this opening.  This type I malformation affects older children and adults.  This is the only type of Chiari that can be acquired.  They are often incidentally found, in other words, they are found by accident.  The type II malformation involves both the brainstem and cerebellum below the foramen magnum.  This is usually associated with spina bifida and myelomeningocele, which is a sac-like opening in the back where the spinal cord is exposed to the air.  This is found in children and sometimes is also known as Arnold-Chiari malformation.  Type III is the most serious and is relatively uncommon.  The cerebellum and the brainstem produce a pouch‑like structure that protrudes from the back of the head and neck, which contains the brain matter.  This type causes severe neurological deficits.

Type IV is also very uncommon and involves an incomplete or underdeveloped cerebellum. 

* There is another form that has recently been suggested, which has been called "borderline" or type 0. This theory is under debate by scientists. Proponents of the theory believe a type 0 Chiari patient would have no protrusion of the cerebellum below the foramen magnum, but would exhibit signs and symptoms of Chiari malformation with a syrinx, a fluid cavity in the spinal cord.

How do patients with Chiari malformation present?

Many patients with type I Chiari malformation do not have symptoms and they are just found by accident.  Patients usually complain about difficulty with neck pain, headaches in the back of the head, balance problems, weakness, numbness and tingling, and headaches that get worse with coughing, or running, or laughing.  They may also complain of ringing in the ears, hearing loss, vomiting, depression, and difficulty using their hands.  In Chiari type II, infants may have symptoms from difficulty swallowing, irritability, drooling, gagging or vomiting, arm weakness, neck stiffness, and developmental delays.

 What are the conditions associated with Chiari malformations?

The patients with Chiari type I or type II malformations can develop hydrocephalus, which is a buildup of spinal fluid in the brain.  The pressure in the back of the brain can block the normal flow of spinal fluid causing fluid buildup.  As mentioned earlier, Chiari type II malformations are associated with spina bifida and myelomeningocele.  Patients with Chiari type I or type II malformations can also develop syringomyelia which is a fluid-filled spinal cord.  This can stretch the spinal cord and result in pain, weakness, stiffness, and bowel and bladder problems.  Tethered cord is associated with Chiari type II malformation secondary to myelomeningocele.  Children who have myelomeningocele have a high risk of developing tethered cord.  Patients with Chiari type I malformations may also develop scoliosis because of the syringomyelia.  Scoliosis is a bending of the spine in different directions affecting the curvature of the spine.  Chiari malformations can also be associated with other skeletal and neurological abnormalities affecting bone growth and fusion of bones in the neck.  They also may have extra folds in the brain.

What is the incidence of Chiari malformation?

It has been estimated that Chiari malformation occurs in about 1 in every 1000 births.  With the advent of MRI, the Chiari malformations are being diagnosed more commonly.

What tests are available to diagnose Chiari malformations?

Many people with Chiari malformations may not have any symptoms and accidentally find them on imaging studies.  MRI is the imaging procedure of choice used to diagnose Chiari malformations.  It is painless and noninvasive and it shows a detailed picture in 3 dimensions of the brain, spinal cord, and brainstem.

What is the treatment for Chiari malformations?

Some Chiari Type I malformations are asymptomatic, in other words they do not cause any symptoms and are just found accidentally and can be observed.  The main treatment for patients with symptoms of Chiari malformation is surgical.  Most patients who have surgery see resolution or reduction in their signs and symptoms.  More than 1 surgery may be needed to treat this condition.  The surgery involves decompression of the posterior fossa, which is the back of the skull.  This procedure involves making an incision in the back of the head and removing a small portion of the foramen magnum and possibly arches in the cervical spine at C1 and C2 to create room for the cerebellum and brainstem.  The dura, which is the covering of the brain, is opened and sometimes this is patched with a graft to create more room for the brain.  (Chiari type II malformations are usually found in infants and children and should be treated in a specialized children’s hospital dealing with myelomeningocele and Chiari type II).  Syringomyelia usually improves after a Chiari Decompression.  Hydrocephalus may be treated with a shunt system, which is a tubing that is inserted in the brain and drains fluid into the abdominal cavity in the chest.  Persistant syringomyelia can be treated with a small tube that is inserted in the spinal cord cyst for long-term drainage.

For more information on NIH, visit chiari malformation.

Chiari Malformation

LastUpdate: 2016-05-11 17:48:15


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