Arnold Chiari II Malformation

What Is It?

The Arnold Chiari II Malformation is a complex version of Chiari malformation. It is a rare congenital anomoly. Unlike the Type I Chiari which is a simpler malformation with only downward displacement of the cerebellar tonsils, the Type II involves many structures including parts of the brain itself. Rather than a normal appearing brain and brainstem with herniated tonsils as in Type I, Type II exhibits deformation of many parts of the brain, particularly malformation of the cerebellum and brain stem, both of which are displaced downward through the foramen magnum. Other structures including the dura covering the brain, the cerebrum and spinal cord can also be involved.

The exact cause of the Chairi II malformation is not known but it is almost always associated with a lumbar myelomeningocele, and abnormality of the development of the end of the spinal cord. Although the cause of myelomeningocele is also unknown, there is some data to suggest a link between this malformation and inadequate levels of folic acid (folate) in the maternal diet.

Most patients with Type II Chiari malformation and myelomeningocele also present with hydrocephalus.

What Types of Symptoms Are Typical?

Infants with this type of malformation can have considerable neurological symptoms. Depending on the severity of the malformation, many of the functions of the cerebellum and lower cranial nerves can be compromised. In particular, respiratory distress and apnea is a frequent feature due to the involvement of the respiratory centers in the brain stem. Severe respiratory compromise can be a cause of significant morbidity and death in these unfortunate infants.

In addition, as mentioned above, these patients with Chiari II malformation usually have concurrent myelomeningocele and hydrocephalus and all the symptomatology which corresponds to those disorders.

How Is The Diagnosis Typically Made?

Like other forms of Arnold-Chiari, Type II malformations are usually diagnosed by an MRI. However, because of the young age of patients at the time of diagnosis, head ultrasound and CT scan is also used in some cases, particularly to evaluate hydrocephalus. As mentioned previously, most of these patients have a concurrent diagnosis of myelomeningocele and hydrocephalus as well.

What Are Some Common Treatments?

There is no cure for Arnold Chiari II malformation. Surgical treatment is somewhat controversial. While surgical decompression of the posterior fossa may reduce crowding of vital brain structures, it does not change the underlying malformation or replace neurological function which is missing. Some patients will be recommended to undergo early decompression. Patients with significant neurological dysfunction, particularly significant respiratory problems, will need intensive care to prevent complications of this disease. Each case is different and each patient and their family should consult their own treating physicians about the best course of action.

It should be noted that these patients often will require surgical treatment for myelomeningocele. In addition, if hydrocephalus is present, a shunting procedure may be required.

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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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