Basilar Invagination

What is basilar invagination?

Basilar invagination is a rare condition that happens when the top of the spine presses into the base of the skull. The condition can be mild or severe. In severe cases, the top of the spine compresses the brain stem and can cause neurological symptoms.

When a child has basilar invagination, a nob at the top of their spine presses into their brain stem.

Anatomy of the spine and basilar invagination

To understand basilar invagination, it helps to understand the structure of the spine and its location next to the brain.

The spine is made up of bones called vertebrae. Together, the vertebrae support the upper body and protect the spinal cord. The neck, also known as the cervical spine, is made up of seven vertebrae known by the letter C and numbers: C1 at the top of the neck through C7 at the bottom.

The joint between the C1 and C2 vertebrae is the most flexible joint in the spine. When you bend your neck to look down or bob or shake your head, this joint allows you to do that. These two vertebrae are connected by a nob on C2. The nob is called the “odontoid process” or “dens” and is about as wide as a pencil.

The C1 and C2 vertebrae at the top of the spine are connected by a nob called the odontoid process.

The top two vertebrae in the cervical spine are connected by a nob called the “odontoid process.”

In a healthy spine, the brain stem, a branch-like bundle of nerves that connects the brain to the spinal cord, exits the skull through a circular opening at the back of the skull and connects to the spinal cord that is surrounded and protected by the vertebrae.

When a child has basilar invagination, the C2 vertebra moves out of alignment and the dens presses up and back into the opening at the back of the skull, putting pressure on the brain stem.

What are the symptoms of basilar invagination?

Symptoms of basilar invagination depend on what part of the brain stem is pinched and to what degree. Many symptoms may flare up when your child bends forward at the neck.

Symptoms may include:

  • headaches
  • neck weakness
  • numbness or tingling in the fingers, arms, toes, or legs
  • dizziness/light headedness
  • trouble swallowing or talking
  • loss of body sense (knowing where body parts are without looking)
  • back pain or shock when bending forward at the neck
  • paralysis in the arms or legs

What causes basilar invagination?

Some children are born with basilar invagination for no known reason. Often, children born with basilar invagination also have Chiari malformation, an abnormality at the base of the skull that pushes some of the brain tissue into the spinal column.

Other genetic conditions such as osteogenesis (fragile bones that break easily) or Marfan syndrome (weak connective tissues) can increase a child’s risk of developing basilar invagination.

Children who were born with irregularities of their cervical spine may also have basilar invagination. In some children, basilar invagination may occur without a clear cause.

How is basilar invagination diagnosed?

Basilar invagination is typically diagnosed and treated by a specialist in spine care, neurology, or neurosurgery. The goal of diagnosis is to determine if the C2 vertebra is out of alignment and, if so, how much.

Typically, diagnosis starts with a physical exam to check your child’s muscles and nerves. The doctor may order one or more of the following imaging tests:

How is basilar invagination treated?

Treatment for basilar invagination depends on the severity of the condition.

Non-surgical treatment for basilar invagination

Children with mild basilar invagination can often be treated with physical therapy, anti-inflammatory medication, or a neck brace. However, basilar invagination may become more severe as children grow. Therefore, children with a mild form of the condition need to be followed by a spine specialist over time. The specialist will monitor their symptoms and watch for any changes in the alignment of their spine.

Surgical treatment for basilar invagination

Children with severe basilar invagination will probably need surgery to relieve pressure on their brain stem and stabilize their cervical spine. Because surgery involves a child’s spine, brain, and spinal cord, it’s important that the surgical team includes experts in both orthopedic surgery and neurosurgery.

Surgical treatment for basilar invagination involves realigning the spine and decompressing any pressure against the brain stem. The cervical spine will then be stabilized with spinal fusion.

How we care for basilar invagination at Boston Children’s Hospital

The Complex Cervical Spine Program at Boston Children’s Hospital is the first and only multidisciplinary pediatric cervical spine clinic in the United States. Our team includes specialists in neurology, neurosurgery, and orthopedic surgery who are experienced in correcting rare and complicated cervical spine disorders like basilar invagination. The extensive expertise and resources at Boston Children’s enable us to treat the most complex cases and perform the most delicate surgeries so our patients can lead full, independent lives.