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Basilar Invagination
Monday, 26 September 2005
Monday, 26 September 2005
Basilar Impression


Basilar invagination is a disorder in which the base of the skull is not formed correctly. As a result, the upper tip of the spine tends to protrude into the area where the spinal cord leaves the brain, and can cause pressure in this area. Basilar invagination and basilar impression are not exactly the same, but the signs, symptoms and treatment are almost identical.


Though mostly found in patients who have other spinal or bone problems, such as Arnold-Chiari malformations or osteogenesis imperfecta, occasionally some children have this problem alone. The exact number of people affected is unknown, but is believed to be extremely unusual.

Signs and Symptoms

If your child has other associated problems, like osteogenesis imperfecta, the basilar invagination may be detected during the evaluation of these problems. Otherwise, the problem can be difficult to detect. The symptoms can include pain in the back of the skull, tingling and numbness in the fourth and fifth fingers or forearm, or tingling in the arms with neck movement. There can be differences in the perception of temperature above and below the belly button, and there can be swallowing problems, speech problems, or difficulty walking. However, importantly, there may be no symptoms at all. This could be dangerous, because if the area in the skull and spine that is not formed right is unstable, the tip of the spine can slip and put pressure on the brain, causing sudden death.

Possible Causes

The cause of the basilar invagination is change in the shape of the bottom of the skull, which can be something the child is born with, or can be associated with other problems such as the Arnold-Chiari malformation, or can develop in diseases that cause softening or deterioration of the bones, such as osteogenesis imperfecta, rickets, juvenile Paget’s disease or rheumatoid arthritis.


This disorder can only be diagnosed by x-ray or MRI. Sometimes an x-ray of the skull can diagnose this, but it may not identify all people who have the disorder. MRI is the standard to diagnose this problem. In the MRI, the radiologist can measure the relationships between the skull, spine and brain, and determine whether there are other associated problems.


The treatment of this disorder is surgery to relieve the pressure on the brain and spinal cord and to stabilize skull and keep it from sinking down further on the spine. There are a variety of different types of surgery used to deal with this problem, and there is considerable debate about which is best. The most common procedure removes the tip of the spine that is protruding and stabilizes the bones around it to try and prevent any progression of the problem.


The ultimate outcome of this disorder is not certain, but deaths have been reported due to the instability of the skull on the spine. Surgery may improve this, but if there were symptoms beforehand, such as weakness or swallowing problems, they may or may not improve. If there are other related problems due to osteogenesis imperfecta or Arnold-Chiari malformation, these may affect the ultimate outcome as well. In some people, the abnormality worsens over time, and in other people it appear to stay the same.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


Because of the rarity, there are few sites devoted exclusively to this problem, and most are written for doctors. Some websites for Arnold-Chiari malformation and osteogenesis imperfecta have limited information about basilar invagination.

Children’s Hospital of Atlanta
This has a reasonably easy to understand explanation of the disorder and its treatment, put together by a group of treating physicians. 

Cedars-Sinai Medical Center
Another explanation written by a treating center, reasonably easy to understand.

Google Search for Basilar Invagination