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What Is Basilar Invagination?

Medically Reviewed by Poonam Sachdev on April 28, 2022

Basilar invagination is when the top of your spine gets pushed into the base of your skull. It leads to pinching or pressure on the brain stem, which is a bundle of nerves connecting the brain to the spinal cord. 

It can be painful and cause various neurological symptoms. Here’s all you need to know about basilar invagination. 

What Is Basilar Invagination?

Basilar invagination is a rare condition that affects the junction where your head meets the neck. It occurs when your neck bone pushes into the opening at your skull’s base. 

Your spine has 33 bones or vertebrae connected by discs. The spine protects the spinal cord and nerves, which connect your body to your brain.

The spine in your neck is made of seven vertebrae, called cervical vertebrae. They are numbered from C1 to C7. C1 is at the top of the spine and supports your skull. C2 lies just below C1 and has an upward peg that enters a hole in C1. The peg lets C1 pivot on C2, which allows you to turn your head sideways.

If C2’s peg pushes into C1 more than it should, it increases pressure on the brain stem. The brain stem is the base of your brain. It is a long, cylindrical stem made of a bundle of nerves that connect the brain to the spinal cord. It leaves the skull and enters the spine through an opening at the base of your skull called the foramen magnum.

When you have basilar invagination, the C2 vertebra pushes into C1 toward the opening in the skull. It can cause the opening or foramen magnum to close. This leads to brain stem compression, which is pinching or pressure on the brain stem.

What Causes Basilar Invagination?

Basilar invagination occurs when you have problems with the neck bones or vertebrae. It can also occur due to platybasia, which is the flattening of the skull’s base. Basilar invagination may be present at birth. But it can develop later due to injury or illness. Vehicle or bike accidents, falls, or accidents during activities like diving can cause basilar invagination.

It may occur in people with the following conditions: 

Basilar invagination is similar to conditions like basilar impression and Chiari malformation. Basilar impression is a mild form of basilar invagination. It occurs due to softening of the neck bones or flattening of the skull’s base.

Chiari malformation is when the brain tissue enters the spine. It is similar to basilar invagination but is present at birth.

What Are Basilar Invagination Symptoms?

BasiIar invagination symptoms can vary based on the pressure on the brain stem, spinal cord, or nerves. You may notice symptoms when you bend your neck. 

BasiIar invagination symptoms include:

  • Headache or pain in the back of the head
  • Feeling dizzy or lightheaded
  • Confusion 
  • Difficulty swallowing or talking due to loss of muscle control caused by nerve damage 
  • Loss of feeling or sensation
  • Inability to tell the position of body parts without looking 
  • Tingling or numbness in hands or feet
  • Tingling when you bend your neck 
  • Twitching eye movements or nystagmus
  • Weakness in the neck, arms, and legs

You may feel a shock down your back when you bend your neck forward. Some may not be able to move their arms or legs, which is called paralysis.

If basilar invagination goes untreated, it can cause complications such as hydrocephalus or syringomyelia. They occur when the flow of fluid around the brain and spinal cord is blocked. The fluid starts collecting in the brain or spinal cord. 

Also, if the lower brainstem gets compressed, it may result in death.

How Is Basilar Invagination Diagnosed?

Your doctor will look for basilar invagination symptoms and ask about your medical history. They’ll use the following tests to check if your spine and nerves are affected:

  1. X-rays
  2. Magnetic resonance imaging (MRI)
  3. Computed tomography (CT) scan
  4. Myelography, which uses x-rays or CT scans to check the spine
  5. Nerve conduction studies, which measure electrical activity in muscles and nerves

How Is Basilar Invagination Treated?

Basilar invagination treatment depends on your symptoms and the severity of your condition. If you have basilar invagination without signs of brain stem compression or pressure on your spinal cord, your doctor will use:

  • Non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin to relieve pain or swelling
  • Neck traction, which involves gently stretching the neck to increase the space between the bones and relieve pressure 
  • A neck collar or brace to support the neck and limit movement 
  • Physical therapy with neck exercises

If you have signs of brain stem compression and nerve problems, you’ll need surgery. Surgery can be done through the nose or mouth. It can also be done at the junction of the head and neck.

Through surgery, doctors aim to decompress or relieve the pressure on the brainstem or spinal cord and stabilize the joint. 

Decompression. This involves a procedure called odontoidectomy. It is the surgical removal of the peg from the C2 vertebra. 

Stabilization. This involves fusing the neck bones with screws and rods to fix or stabilize the joint. Doctors may also use bone transplants or grafts. They are pieces of bone taken from elsewhere and placed into the joint. This bone grows and fuses with the problematic joint to make it stable.

Outlook

If you have basilar invagination symptoms, visit your doctor immediately for diagnosis and treatment. Delaying treatment can worsen the symptoms.

Surgery can improve your condition. But some people may not recover completely. Some neurological symptoms may remain even after treatment. This is why doctors recommend rehabilitation after treatment.

You’ll have to visit a physical therapist to improve muscle movement. Apart from this, you may have to visit a speech and occupational therapist. You’ll also have to visit your doctor for follow-up sessions to check your progress. If your symptoms worsen or you notice new symptoms, contact your doctor immediately.

Show Sources

Sources:

Cedars Sinai: “Basilar Invagination.”

Columbia University Irving Medical Center: “Basilar Invagination.”

Donnally III, C.J., Munakomi, S., Varacallo, M. StatPearls, “Basilar Invagination,” StatPearls Publishing, 2022.

KidsHealth: “Basilar Invagination.”

UT Southwestern Medical Center: “Basilar Invagination, Basilar Impression, and Cranial Settling.”

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