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What

An Arnold-Chiari Malformation (ACM) occurs when the brain forms incorrectly. This abnormality occurs very early in pregnancy, when the brain is still forming. This malformation involves the base, or bottom, of the brain, where the skull and the spine meet. This malformation results in some of the brain’s structures being moved downward into the spinal canal. This pushing down of the brain into the spinal canal can lead to pressure on the lower parts of the brain and spinal cord. The symptoms found with this malformation are related to the damage done to the lower parts of the brain and spinal cord. The amount of displacement of the brain’s structures determines the type and severity of the Arnold Chiari Malformation. There are four types of Arnold Chiari Malformation called ACM 1, ACM 2, ACM 3, and ACM 4.

Who

An Arnold Chiari malformation can occur in all ethnic groups and in both females and males. For unknown reasons, there is a slightly higher rate of occurrence among females. Rarely, this has been found in several members of one family, but it is not known if any genes are involved. While the malformation is present from birth, symptoms sometimes do not appear until childhood or adulthood.

Signs and Symptoms

Symptoms can vary according to the type of ACM. In general, the symptoms of the type I malformations are less severe than that of the type II malformation. ACM 1 symptoms: • Pain: headache, neck pain, arm pain, leg pain (the most common symptom) • Weakness in the arms and legs (more in the arms) • Change of feeling in the arms and legs • Difficulty with balance and coordination • Double vision • Slurred speech • Difficulty swallowing • Vomiting • Ringing in the ears (tinnitus) • Abnormally high muscle tightness ACM 2 symptoms are due to brain stem and cranial nerve damage. Most people who have this malformation have these symptoms in early childhood or in the newborn period. Symptoms include: • Swallowing difficulties: which result in poor eating, cyanosis (turning blue) during feeding, swallowed food coming out through the nose, prolonged feeding time, drooling • Apneic spells (periods when the child does not breathe) • Stridor (difficulty taking a breath) • Aspiration (food entering the lungs) • Arm weakness • Nystagmus (abnormal eye movements) • Weak or absent cry • Progressive scoliosis (curvature of the spine) • Weakness of the muscles of the face Untreated, ACM can lead to very serious consequences including paralysis.

Possible Causes

The cause of an Arnold Chiari Malformation is unknown. It is thought that the bones of the skull may form incorrectly and that this may cause the brain to form incorrectly. The four types of ACM are divided according to the severity and how much of the brain is moved down into the skull’s opening. Listed below are the structural and functional causes of each type of ACM. ACM 1: Involves a part of the brain called the cerebellar tonsils. This is the part of the brain found on the back and underside of the brain. No other brain structures are displaced in ACM 1. The protrusion of brain tissue may also interfere with the flow of CSF (Cerebral Spinal Fluid- the fluid that bathes the brain and the spinal cord) to and from the brain. There is frequently an associated accumulation of fluid within the spinal cord (syringomyelia). ACM 2: This type also involves the cerebellar tonsils, but also includes the brain stem and other near by brain structures. This form of the malformation may be accompanied by syringomyelia, hydrocephalus (the accumulation of fluid in the brain), and spina bifida. (Spina bifida is a disorder that occurs from birth in which the vertebrae fail to close or completely encircle the spinal cord.) ACM 3: This more severe form includes all of the characteristics listed in ACM 1 and ACM 2 plus a fluid-filled, balloon-like bulge of the spinal cord in the neck region (myelomeningocele) that may contain CSF, and/or tissue from the spinal cord. ACM 4: In this very rare form, there is incomplete or total lack of development of the cerebellum. There is no protrusion of brain structures into the spinal canal in this form of ACM.

Diagnosis

When the diagnosis of Arnold Chiari is suspected, the diagnostic tool of choice is a specialized photographic-like study called a MRI (magnetic resonance imaging) scan. This test easily shows the protrusion of the brain substance through the skull’s opening and into the spinal canal. If there is abnormal fluid accumulation this will also be visible with an MRI scan. These malformations are very difficult to see on CT (computed tomography) scans and almost impossible to see on plain x-rays, however CT scans can identify abnormal bone structure in the skull if it is present.

Treatment

There are many ways to treat these malformations, but all require surgery. The basic concept of the operation is to uncrowd the area at the base of the cerebellum (part of the brain) where it is pushing against the brainstem and spinal cord. This is done by removing a small portion of bone at the base of the skull as well as often removing a part of the back of some of the vertebrae. The operation is often modified if there is a syringomyelia (fluid accumulation in the spinal cord) present or if the child has hydrocephalus (fluid accumulation in the brain). This abnormal fluid accumulation must be dealt with prior to the surgical treatment. Typically, a shunt is inserted to establish a pathway for continued drainage of the fluid-filled region. The main goal of the surgical therapy is to stop the progression of symptoms. This goal is achieved in the most cases.

Prognosis

Most children who have the surgery do very well and have improvement in their symptoms. Generally, children do better than newborns. Children should be watched closely to monitor for any signs or symptoms which may indicate that there is a recurrence. While most children have a great deal of improvement after surgery there may be permanent damage that cannot be corrected. Children who receive surgical treatment for this condition are expected to have a normal life span.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

World Arnold Chiari Malformation Association
The website has an online support group, links to current studies, contact information of group members.

Columbia University Pediatric Neurosurgery
Site contains information about Chiari Malformations and has links to information on surgical treatment and research.

Wake Forest University Dept. of Neurosurgery
Site contains links to information about Arnold-Chiari and Syringomyelia

Google Search for Arnold Chiari Malformation (ACM)

References and Sources

1. Andreoli (2001), Chapter 4 Developmental and Neurocutaneous Disorders, CECIL Essentials of Medicine 5th Ed., Saunders p. 939 2. www.nyneurosurgery.org/chiari_diagnosis.htm 3. www.cpmcnet.columbia.edu/dept/nsg/psn/ChiariMalformation.html 4. www.ninds.nih.gov.health_and_medical/disorders/chiari_doc.htm