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Chiari Malformation: An Abnormality Of the Skull Base

Chiari Malformation: An Abnormality Of the Skull Base
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Chiari Malformation


Chiari Malformation is a deformity of the back, bottom portion of the skull. This deformity results in herniation of the cerebellum, the bottom, hind portion of the brain. The bottom of the skull is too small, leaving little room for the cerebellum to fit comfortably. This causes a portion of the cerebellum to herniate downwards into the spinal canal. This herniated brain matter is referred to as the “cerebellar tonsils.” Herniation of this brain matter can lead to several serious medical problems. The cerebellar tonsils can create pressure on the brainstem, which can result in impaired autonomic functions or sleep apnea. The cerebellar tonsils can also block cerebrospinal fluid from flowing freely throughout the spinal canal. This results in an accumulation of fluid in the spinal cord, which is called a syrinx. It can also lead to an accumulation of cerebrospinal fluid in the brain, which is called hydrocephalus.

What Causes Chiari Malformation?

Many people who have Chiari have no idea they have it until symptoms arise. In most cases, Chiari is congenital. This means that it is present at birth. With that said, there have been some recorded cases of acquired Chiari from traumatic events such as car accidents.

Types of Chiari Malformation

There are five different types of Chiari Malformation, with each one more severe than the prior. You do not progress from one type to another.

Chiari 1

Chiari 1 is the most common type of Chiari Malformation. This type refers to the lower part of the cerebellum, the cerebellar tonsils, extending downward into the spinal canal. Previously, medical literature stated that cerebellar tonsils extending less than 5mm past the foramen magnum were not considered Chiari. Despite this, recent studies show that patients whose cerebellar tonsils extend less than 5mm into the foramen magnum can have symptoms just as severe as those with larger herniations.

Chiari 1.5

Chiari 1.5 has only just recently been recognized as a type of Chiari Malformation. In this type of Chiari, the cerebellar tonsils and brainstem both herniate downwards into the spinal canal. This may result in very serious medical complications, such as severe brainstem compression.

Chiari 2

Chiari 2 is a more serious type than the previous two. It is evident early in infancy and can lead to life-threatening complications. Chiari 2 occurs when both the cerebellum and the brainstem herniate downwards into the spinal canal along with the presence of a myelomeningocele. A myelomeningocele is a form of spinal bifida that occurs when the spinal canal and backbone fail to close before birth.

Chiari 3

Chiari 3 is a very rare and very serious type of Chiari Malformation. This type occurs when the cerebellum and brainstem protrude out of an opening in the back of the skull. Babies born with this type of Chiari typically suffer life-threatening complications and ultimately have a very poor prognosis.

Chiari 4

Chiari 4 is the rarest type of Chiari Malformation. This type refers to the incomplete development of the cerebellum. In this type of Chiari, entire parts of the cerebellum do not develop and portions of the spinal cord may be visible outside the spinal column.

Chiari Malformation Symptoms

Chiari Malformation can lead to a multitude of wide-ranging symptoms including, but not limited to the following:

  • Headaches
  • Dizziness
  • Fainting
  • Head Pressure
  • Heart Palpitations/Tachycardia
  • Ringing in the Ears
  • Difficulty Swallowing
  • Difficulty Breathing/Shortness of Breath
  • Nausea
  • Vomiting
  • Numbness and Tingling in Extremities
  • Weakness in Extremities
  • Sleep Disturbances/Sleep Apnea
  • Visual Disturbances and Blurry Vision
  • Incontinence
  • Difficulty With Fine Motor Skills
  • Neck Pain
  • Back Pain
  • Pain in the Extremities
  • Loss of Coordination
  • Memory Issues
  • Seizures

Diagnosing Chiari Malformation

In some cases of Chiari Malformation, the condition can be diagnosed through a CT scan of the brain. However, the preferred method is an MRI of the brain. An MRI scan can provide a more detailed picture of the Chiari Malformation. With the diagnosis of Chiari Malformation, it is recommended the patient have a full spinal MRI to check the spinal cord for syrinx formation.
For many patients, it takes years or even decades to diagnose Chiari Malformation. Since the condition presents such wide-ranging symptoms, it is notoriously misdiagnosed as other conditions. If a patient suspects they have Chiari Malformation, they may want to request a CT scan or MRI of the brain.

Treating Chiari Malformation

If Chiari Malformation is found inadvertently and the patient is not experiencing symptoms, no treatment may be necessary. Once a patient has become symptomatic, the only treatment for Chiari Malformation is brain surgery. This surgery is essentially to “decompress” the herniated brain matter and resolve any brainstem compression or cerebrospinal fluid blockage. Decompression surgery consists of removing a small portion of bone at the bottom of the skull, giving more room for the cerebellum to sit comfortably. If the cerebellar tonsils extend further down into the spinal column, the back of the C1 and C2 vertebrae may be removed as well. Many surgeons will also expand the dura, the outer casing of the brain, using a dural patch made from the patient’s own muscular tissue. In some cases, the herniated portion of the cerebellum may need to be cauterized or resected to make more room for cerebrospinal fluid flow. It is important to note that since Chiari Malformation is a structural deformity, rather than a disease, it cannot be cured. Surgery is only used to alleviate symptoms and decrease the likelihood of progression.

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