This is a rare condition. To understand it, it is important to know how the spine works. The spine is made up of 33 bones, or vertebrae. These and the discs between them provide a passage for the spinal cord and nerves. The spinal cord itself connects the nerves of the body to the brain.
Basilar invagination occurs when the top of the second vertebrae moves upward. It can cause the opening in the skull where the spinal cord passes through to the brain (the foramen magnum) to close. It also may press on the lower brainstem. The brainstem is a stalk-like part of the brain that connects the main portion of the brain to the spinal cord.
This is similar to Chiari malformation. That, however, usually is present at birth.
If there is pressure on the lower brainstem, its first symptom may be death. Otherwise symptoms vary depending on whether the spinal cord, brain stem, nerves or their blood supply is affected by the pressure.
Symptoms become apparent when the neck is bent. They include:
- Periods of confusion or conscious awareness that doesn't seem normal
- Difficulty swallowing or saying words due to loss of muscle control after damage to the nervous system (dysarthria)
- Loss of sensation
- Pain in the back of the head
- Loss of the ability to know how joints are positioned
- Tingling or numbness in the fourth and fifth fingers
- Tingling or numbness in the middle part of the forearm
- Tingling when the neck bends forward or backward
- Weakness or stiff,awkward movements of the of the arms and legs
Patients will go into a pool and notice that below the belly button the water is not as cold as it is above.
Causes and Risk Factors
Basilar invagination can be present at birth. If the condition develops after birth, it is usually the result of injury or diseases. If due to injury, about half the time it is caused by vehicle or bicycle accidents; 25% of the time by falls and 10% of the time by recreational activities such as diving accidents.
A doctor will base his or her diagnosis on the symptoms the patient has and the results of tests, including:
If there aren't neurological symptoms (such as difficulties moving, loss of sensation, confusion, etc.) and there is no evidence of pressure on the spinal cord, a conservative approach may be taken such as:
- Drugs, such as aspirin, without steroids to relieve inflammation (tenderness and swelling)
- Neck traction, in which the neck is pulled along its length, thus relieving pressure on the spinal cord
- Using a neck collar
If there is pressure on the spinal cord, surgery is recommended.