Arnold Chiari III Malformation

What Is It?

The Type III Arnold Chiari malformation is a complex malformation of the hindbrain and cranicervical junction. It is characterized by downward displacement of the hindbrain including the cerebellum, as in the case of Type II Chiari malformation. However, the Chiari III malformation is associated with an occipital encephalocele, rather than a lumbar myelomeningocele as usually seen in Type II.

An encephalocele is a defect in the development of a part of the brain and its coverings including the meninges and the skull. This usually presents as a bulging sac on the head with undeveloped brain tissue within. Encephaloceles can occur anywhere along the midline of the skull. In the case of Type III Chiari malformation, the associated encephalocele is at the back base of the brain and skull, called an occipital encephalocele. It is usually associated with an underdeveloped cerebellum.

What Types of Symptoms Are Typical?

The symptoms of a Type III Chiari are variable depending on the severity of the disease. In severe cases there can be quite severe brainstem and cerebellum involvement which can cause many neurological symptoms. Like the Type II, if the respiratory centers in the brainstem are involved, the infant may experience severe respiratory distress and apnea.

As with a Type II, Chiari III can be associated with hydrocephalus and other neurological disease.

How Is The Diagnosis Typically Made?

The encephalocele associated with Type III Chiari draws attention to the area. To further evaluate the internal anatomy, like other forms of Chiari formation, Type III malformations are usually evaluated 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.

What Are Some Common Treatments?

Treatment of Arnold Chiari III malformation varies depending on the specific malformation and clinical features of each patient. Patients and their families should consult their own treating physicians about the management options. Many patients with an encephalocele will require surgical treatment to close the encephalocele, with or without some form of surgical decompression of the posterior fossa in the area of the malformation.

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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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