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Chiari Malformation

What are Chiari Malformations? Chiari malformations (CMs) are structural defects in the cerebellum, the part of the brain that controls balance. When the indented bony space at the lower rear of the skull is smaller than normal, the cerebellum and brain stem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid (the liquid that surrounds and protects the brain and spinal cord) and can cause a range of symptoms including dizziness, muscle weakness, numbness, vision problems, headache, and problems with balance and coordination.

Symptoms may change for some individuals depending on buildup of CNS and any resulting pressure on tissue and nerves. CMs are classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal. The most common is Type I, which may not cause symptoms and is often found by accident during an examination for another condition. Type II (also called Arnold-Chiari malformation) is usually accompanied by a myelomeningocele-a form of spina bifida that occurs when the spinal canal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening. Type III is the most serious form of CM, and causes severe neurological defects. Other conditions sometimes associated with CM include hydrocephalus, syringomyelia (a fluid-filled cyst in the spinal cord), and spinal curvature.

Chiari Frequently Asked Questions:

These FAQ's are for informational purposes only and in no way represent an attempt to provide medical advice. This information may or may not apply to your case and anyone with a question or concern about their health is strongly encouraged to consult with a medical professional.

1. What is a Chiari Malformation?

Chiari Malformation Type I (CM) is a neurological disorder where part of the brain, the cerebellum (or more specifically the cerebellar tonsils), descends out of the skull into the spinal area. This results in compression of parts of the brain and spinal cord, and disrupts the normal flow of cerebrospinal fluid (a clear fluid which bathes the brain and spinal cord).

2. Is Arnold-Chiari different from Chiari?

Not everyone uses the same terminology when describing Chiari. Some people use Arnold-Chiari (ACM) interchangeably with Chiari. Others only use Arnold-Chiari to refer to Chiari Type II which involves more of the brain descending out of the skull, is predominantly diagnosed in children, and is commonly associated with Spina Bifida. Other terms for Chiari include tonsillar ectopia and hindbrain herniation, meaning the cerebellar tonsils are out of position.

3. What are the symptoms?

Because Chiari involves the nervous system, symptoms can be numerous and varied. In fact, one large study showed that the vast majority of Chiari patients reported 5 or more symptoms, and 49 distinct symptoms were reported by 2 or more patients. Despite this variety, the most common Chiari symptom, and the hallmark of the disease, is a headache. Usually, the Chiari headache is described as an intense pressure in the back of the head and is brought on, or aggravated, by exercise, straining, coughing, sneezing, laughing, bending over, or similar activities. Other common symptoms include balance problems and fullness in the ears. In very young children, trouble swallowing is one of the most frequent symptoms. When thinking about symptoms, it is also important to keep in mind that once a person's health is compromised in one way (with Chiari for example), secondary problems are more likely to develop, especially if a person is in chronic pain. Research has shown that people with chronic pain are much more likely to develop other chronic conditions, so not every symptom may be a direct result of a Chiari Malformation.

4. Does the size of the malformation matter?

Traditionally, Chiari Malformation has been defined as the cerebellar tonsils descending more than 3-5mm out of the skull. However, research has shown there is no real correlation between the amount of descent (or herniation) and clinical symptoms. Some people with herniations of less than 3mm are extremely symptomatic and some people with quite large herniations are symptom free. Because of this, doctors are now focusing on whether the cerebellar tonsils block the normal flow of cerebrospinal fluid (CSF). The current theory is that disruption of CSF flow is a more important measure than the size of the herniation.

5. How is a Chiari Malformation diagnosed?

An MRI (Magnetic Resonance Imaging - a non-invasive test which uses a large magnet to create a picture of internal organs) can clearly show if the cerebellar tonsils are out of position. However, since the definition of Chiari is changing, most doctors will use a combination of reported symptoms, a neurological exam, MRI results, and their experience and judgment to determine if a person has Chiari. Unfortunately, there is no single, objective test which can clearly say that someone has a Chiari malformation which is causing problems.

6. What is a cine MRI?

Cine MRI is a type of MRI where the machine is programmed to measure the flow of cerebrospinal fluid (CSF). Doctors use this to see if the cerebellar tonsils are blocking the normal flow of CSF from the brain to the spinal area and back. While many doctors now consider cine MRI to be a routine test in diagnosing Chiari, some experts question it's usefulness and are reserving judgment.

7. What is a borderline Chiari?

Since Chiari was traditionally defined based on the size of tonsillar herniation, a borderline Chiari can refer to when the cerebellar tonsils are descended only a couple of millimeters out of the skull. Alternatively, borderline Chiari can refer to someone with mild symptoms which may not be directly attributable to Chiari.

8. How did I get this condition?

Chiari was originally thought to be a congenital condition - meaning you are born with it. While this may be true for many people, published case studies have also demonstrated that Chiari can be acquired and even reverse itself if the source of the problem is removed. It is not known how many cases are congenital and how many are acquired. Complicating the situation is that for reasons that aren't clear, some people develop symptoms as children, and some people develop symptoms as adults. What triggers symptoms is not fully understood.

9. I don't have any symptoms, but an MRI shows a malformation. What does this mean?

This is sometimes referred to as an incidental finding. Someone has an MRI for an unrelated reason, but it shows a Chiari malformation - meaning the cerebellar tonsils are descended - yet the person has no Chiari type symptoms. As MRI's become more common, this is happening more frequently and is one reason that diagnosing Chiari can be difficult and cannot be based on an MRI alone.

10. Does Chiari run in families?

An ongoing study at Duke University has identified more than 100 families where two or more members are affected by Chiari. This implies that for some cases there is a genetic basis for Chiari. It is not known, however, what percent of cases may have a genetic component. In other words, this does not mean that the family of everyone with Chiari is carrying a Chiari gene.

11. Will my children get it? Is there a genetic test to see if someone has Chiari?

A Chiari gene has not yet been identified, so there is currently no genetic test.

12. How is Chiari treated?

If the symptoms aren't severe, doctors may recommend just monitoring the situation with regular MRI's and treating the symptoms individually. However, if symptoms are interfering with quality of life, are getting worse, or if the nervous system is being impaired, doctors may recommend surgery. The most common surgical treatment, performed by a neurosurgeon, is known as decompression surgery. An alternative surgery involves placing a shunt (a tube-like device) to channel the flow of CSF and relieve pressure.

13. How do I know whether to have surgery?

The decision whether to have surgery is up to each individual and their doctor. Some of the factors that are considered are the severity of symptoms, whether the symptoms are getting worse, whether the nervous system is being compromised, whether there are any complicating issues, and the surgeon's own experience and judgment. Unfortunately, there is no single, objective measure to say whether someone should have surgery and many patients will find that different doctors may have different opinions. Some doctors are more aggressive in their treatment approach and some are more conservative.

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