Chiari malformation: what is it and why does it occur?

Chiari malformation is a condition of the central nervous system. It actually comprises a group of complex abnormalities in which part of the brain tissue extends into the vertebral canal.

This pathology usually appears in people who have a small skull or with some deformity. Although many patients can remain asymptomatic for years, very serious cases are also reported.

Fortunately, there are currently different forms of treatment. However, there is no zero risk either. In this article we explain everything you need to know about the Chiari malformation and how it is approached.

What is Chiari malformation?

The Chiari malformation, as we have pointed out in the introduction, encompasses a group of brain abnormalities. According to an article in the National Organization for Rare Disorders, most cases are congenital. That is, the problem is present from birth.

To understand Chiari malformation, one must know what the anatomy of the brain and spinal cord is like. The brain and spinal cord are connected to each other by a thick bundle of nerves, which pass through a hole called foramen magnum.

The cerebellum is housed on the base of the skull. It is one of the organs that is part of the brain and is responsible for balance and coordination. Specific parts of it are called cerebellar tonsils.

What happens in Chiari malformation is that the cerebellar tonsils exceed the foramen magnum. In this way, they move from their usual place on the posterior fossa and access the spinal canal.

As explained in an article published in American Association of Neurological Surgeons, most of the people with this disease are asymptomatic. It is estimated that it affects 1 in every 1000 inhabitants in the general population.

The cerebellum is an organ located behind and below the brain, with functions related to balance and coordination.

Types of Chiari malformation

Chiari malformation can be of different types, depending on the anatomy of the injury and the symptoms. In general, four variants are distinguished.

Type I

Chiari type I malformation is one of the most common. It usually causes few symptoms, so it is not detected until adulthood. In addition, it is not associated with any other neurological problem.

Type II

This type is more serious than the previous one. What happens is that the cerebellar tissue penetrates further into the spinal canal. It is usually accompanied by hydrocephalus, which is the excessive accumulation of cerebrospinal fluid.

This accumulation causes the intracranial pressure to increase. This is why vomiting, seizures and irritability may appear. It is also associated with spina bifida and myelomeningocele.

So, These children are likely to have paralysis or an inability to control their bowels. Due to the severity of the condition and its associations, type II Chiari malformation is diagnosed very early.

Type III

This type is rarer than type II, but more serious. It is associated with encephalocele. It is a pathology that consists of part of the brain and the meninges protruding through the skull. The reason is that there is no proper closure of the cranial bones. Mortality is very high.

Type IV

Chiari type IV malformation differs greatly from the previous ones. The cerebellum is not herniated through the foramen magnum. What happens is that it does not develop normally. Most patients die in infancy.

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What symptoms does this pathology produce?

As we have explained throughout the article, Chiari malformation doesn't always cause symptoms. In fact, as the most common is type I, most cases are not detected or diagnosed in adulthood.

As explained by specialists from the Mayo Clinic, in the type I variant, headaches are common. This pain is aggravated by coughing, sneezing, or straining. Dizziness, unsteady gait, poor coordination, and neck pain are also common.

Although it is less usual, some patients experience breathing abnormalities and have a slow heart rate. There may be constant ringing in the ears and weakness.

In type II the symptoms are similar. However, those produced by myelomeningocele are added to them. That is why it is more common to have swallowing problems, weak arms and respiratory disorders. In type III there are even more neurological disorders and mortality is very high.

Causes and risk factors

Chiari malformation occurs because part of the cerebellum herniates into the spinal canal. This happens due to a deformed or too small base of the skull.

It is believed that there may be a hereditary component in the development of the disease. However, to this day it is unknown exactly why. Genetic mutations that cause alterations in brain development have been identified, but research is still ongoing.

Possible complications of Chiari malformation

Chiari malformation, depending on the type, can be very serious. As we have seen, type II is frequently associated with hydrocephalus, spina bifida, and syringomyelia. What happens in spina bifida is that part of the spinal cord is exposed.

Syringomyelia, on the other hand, consists of the formation of a cyst within the spinal column. This disease can also lead to tethered spinal cord syndrome. It is a problem that tends to cause serious damage to the nerves.

You might be interested in: Syringomyelia: causes, symptoms and complications

How is it diagnosed?

Although, in some cases, the clinic can guide the diagnosis almost decisively, complementary tests are usually needed. Magnetic resonance imaging is one of the most useful in Chiari malformation.

It allows obtaining detailed images of the structures of the brain and spinal cord. In addition, it does not use radiation, so it is harmless for the patient. Another option is to do a CT scan.

An MRI is an appropriate study to determine the presence of Chiari malformation.

Treatments currently available

Chiari malformation is not always treated. Asymptomatic people usually remain for follow-up only. In fact, if only mild headaches appear, the first thing to do is try to eliminate them with common painkillers.

However, if symptoms are severe, surgery is the only option. According to an article in the National Institute of Neurological Disorders and Stroke, the goal is to reduce intracranial pressure caused by hydrocephalus. To do this, an attempt is made to decompress the posterior fossa, severing a part of that bone.

In this way, the cerebrospinal fluid can circulate again normally. Another option is to perform decompression at the level of the spinal cord. The surgical technique varies depending on the type of malformation and associated disorders.

For example, if there is syringomyelia or hydrocephalus, a special drainage for the cerebrospinal fluid is usually required. In many cases, if the malformation is detected before birth prenatal surgery can be tried.

It is important to bear in mind that these are very complex surgeries. Like any other intervention, there is a risk of infection, healing problems and bleeding. In addition, there may be fluid leaks or nerve sequelae.

So, it is always preferable to leave this option reserved for severe cases. In fact, some people who have surgery already have irreversible nerve damage prior to surgery, so the result may not be as expected.

Chiari malformation can be very serious

Chiari malformation encompasses different cerebellar abnormalities. In general, what happens is that part of the cerebellum herniates into the spinal canal. In addition, in several types there are associations with other serious malformations, such as encephalocele and meningocele.

It is essential to try to diagnose this pathology as soon as possible. If treatment is started early, irreversible damage to nerve structures can be prevented.

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