Chiari Malformation: A Basic Overview
Chiari malformation is a condition that causes brain tissue to settle into the spinal
canal. It develops where your skull and neck (cervical spine) come together; when part of
the skull is either too small or misshapen, part of the brain can settle into the foramen
magnum. The foramen magnum is a large opening at the bottom of your skull. Nerves from the
brain go through it and into the spinal canal, joining the spinal cord.
The brain shouldn't press through the foramen magnum; there should only be nerves in
there. If the brain does press into the foramen magnum, that's a Chiari malformation.
You can visualize a Chiari malformation by thinking about a funnel. The foramen magnum is
the skinny part at the bottom, and above that is where the brain should rest. With a
Chiari malformation, though, the brain goes into the skinny part of the funnel.
Chiari malformation can be caused by a structural problem with the brain, skull, or spinal
canal. Those structural problems can be present at birth, those are congenital defects.
Chiari malformation caused by structural defects is also called primary Chiari
malformation; it isn't caused by any other condition.
Secondary Chiari malformations are caused by something else, ost often by surgery. This is
very rare, but it is possible to develop a Chiari malformation after having surgery to
remove a tumor in the skull/neck area. The surgeon may remove too much bone along with the
tumor, allowing the brain to settle into the foramen magnum.
It's also possible to develop a more severe Chiari malformation after surgery to correct a
primary Chiari malformation. During a posterior fossa decompression, the surgeon may
remove too much bone, making it possible for the brain to settle further into the spinal
canal. Again: this is very rare, but it is a possible complication of Chiari malformation
surgery, one you should review with your surgeon.
There are four types of Chiari malformations, categorized by how much of the brain is
protruding into the spinal canal.
Type I: This is the adult version of Chiari malformation, and it's also the most
common. It's generally first noticed during adolescence or adulthood, and often, it's
discovered during an examination for something else, most people don't realize that they
have Chiari malformation, unless the symptoms are quite severe.
In Type I Chiari malformation, part of the brain settles into the foramen magnum,
the cerebellar tonsils, to be exact, is the part going into the foramen magnum.
Type II: This is one of the pediatric version of Chiari malformation. More brain
tissue pushes through the foramen magnum in Type II: the cerebellar tonsils and a portion
of the brainstem protrude. Because more tissue is protruding, the symptoms are more severe
with Type II than with Type I.
Also, Type II always involves myelomeningocele, a form of spina bifida. With
myelomeningocele, the vertebrae and spinal canal don't close correctly before birth, so
the spinal cord isn't protected.
Type II is called Arnold-Chiari malformation.
Type III: This is also a form that affects children, and it's more severe than
Types I or II. In it, a significant portion of the brain, the cerebellum, and the
brainstem push all the way through the foramen magnum and into the spinal canal.
Type IV: This is the most severe form of Chiari malformation. In Type IV, the
brain doesn't develop as it should.
A Chiari malformation can disrupt the flow of cerebrospinal fluid (CSF). CSF is necessary
to protect your brain and spinal cord, and if it can't flow normally, then it's more
difficult for your brain and spinal cord to send and receive nerve messages.
The pressure caused by parts of the brain pushing through the foramen magnum can also
cause nerve problems.
As you can tell, the majority of Chiari malformation symptoms relate to neurological
problems. The symptoms do vary based on the type and severity, but the most common symptom
is a headache. People with a Chiari malformation generally have headaches in the occipital
region of the brain; that's the back of your head, right where you skull joins with your
cervical spine (neck). These headaches are generally aggravated by particular positions
and actions, including tilting your head back and coughing.
Some other typical symptoms include:
- balance problems
- difficulty with fine motor skills (e.g., writing)
- vision issues
- trouble swallowing
For some patients, symptoms can come and go because they're dependent upon how much
CSF has built up.
Patients with Type I Chiari malformation may not have any symptoms, it all depends on the
severity of the condition.
The best way to diagnose Chiari malformation is with a magnetic resonance imaging test, an
MRI. The MRI will show the doctor the various parts of your brain, skull, spinal cord, and
spinal canal; he or she will be able to see any abnormalities that could point to Chiari
The recommended treatment depends on the severity of the Chiari malformation. As mentioned
above, it is possible to have Chiari malformation and not have any symptoms, then you
won't need treatment.
If you have pain, the doctor may suggest various pain medications to help control the
pain. You may need to take a non-steroidal anti-inflammatory (NSAID), a medication that
works to reduce inflammation as a way to reduce pain. Or you may need an analgesic, a pain
killer. Both NSAIDs and analgesics come in over-the-counter and prescription strength,
your doctor will work with you to figure out the best medication for your pain.
Surgery can be used to relieve some symptoms of Chiari malformation; surgery is the only
way to relieve the pressure on the spinal cord and nerves caused by the malformation. The
goal of surgery is to stop the malformation from getting worse.
Typically, surgeons use a posterior fossa decompression. In that surgery, the surgeon
removes part of the skull to make more room for the brain. The surgery takes pressure off
the brain and spinal cord, decompression means "to take pressure off", and should reduce
the neurological symptoms and problems. The surgeon may also do laminectomies at C1 and
C2, the first and second levels of the cervical spine. The laminectomies are also supposed
to make more room for the brain.
Also in a posterior fossa decompression, the surgeon may increase the size of the dura,
the sac around the brain. He or she does that by putting in a patch, made from either
animal-derived or synthetic tissues, that will grow into the dura. The patch will make the
dura bigger, giving more room for the brain. Not every surgery to treat a Chiari
malformation will involve this dural patch.