Arnold-Chiari malformations, often referred to simply as Chiari malformations, are a group of congenital (present at birth) structural abnormalities in the brain and spinal cord. These malformations involve the cerebellum, which is the part of the brain responsible for coordinating voluntary muscle movements, and the brainstem, which connects the brain to the spinal cord. Chiari malformations are named after the Austrian pathologist Hans Chiari, who first described them in the late 19th century, and the American pathologist Julius Arnold.

There are several types of Chiari malformations, with Type I and Type II being the most common:

1. Chiari Type I (CM-I): This is the most common type of Chiari malformation. In CM-I, the cerebellar tonsils (the lower part of the cerebellum) extend downward into the upper spinal canal through the foramen magnum, which is the opening at the base of the skull. This can block the flow of cerebrospinal fluid (CSF) and put pressure on the brainstem, causing a variety of symptoms.

2. Chiari Type II (CM-II): CM-II is typically associated with a more severe form of spina bifida called myelomeningocele. In this type, both the cerebellar tonsils and the brainstem are displaced downward into the spinal canal. It often presents with more pronounced neurological issues and is usually diagnosed shortly after birth.

3. Chiari Type III (CM-III): CM-III is extremely rare and involves even more significant herniation of the cerebellum and brainstem into the spinal canal. It is often associated with severe neurological deficits and is frequently fatal.

4. Chiari Type IV (CM-IV): CM-IV is also very rare and involves an underdeveloped cerebellum. This type is often associated with other brain abnormalities and is usually diagnosed in infancy or early childhood.

The exact cause of Chiari malformations is not always clear, but they are thought to result from a combination of genetic and environmental factors. Most often, Chiari malformations are diagnosed during childhood or adolescence, although they can go unnoticed until adulthood.

Symptoms of Chiari malformations can vary widely and may include:

- Headaches, particularly at the back of the head and worsened by coughing or straining.
- Neck pain.
- Dizziness.
- Balance and coordination problems.
- Muscle weakness.
- Numbness or tingling in the hands and feet.
- Difficulty swallowing.
- Breathing problems, particularly in severe cases.

Treatment for Chiari malformations depends on the severity of the condition and the specific symptoms. In some cases, conservative approaches like pain management and physical therapy may be sufficient. However, more severe cases may require surgical intervention to relieve pressure on the brainstem and restore normal CSF flow. Surgery often involves removing a small portion of the bone at the back of the skull and spine (craniectomy and laminectomy) to create more space for the brain and spinal cord.

It's essential for individuals with Chiari malformations to work closely with healthcare professionals to manage their condition and address any related symptoms or complications. Regular medical follow-ups are typically recommended to monitor the condition's progression and ensure appropriate care.

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