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Chiari Malformations (CM) are structural defects in the cerebellum (the
part of the brain that controls balance). When the indented bony space
at the lower rear of the skull is smaller than normal, the cerebellum
and brainstem can be pushed downward. The resulting pressure on the cerebellum
can block the flow of cerebrospinal fluid (the liquid that surrounds and
protects the brain and spinal cord). There are three primary types of
CM. The most common is Type I, which occurs during fetal development and
may not cause symptoms and is often found by accident during an examination
for another condition. Type II (also called Arnold-Chiari malformation)
is usually accompanied by a myelomeningocele, a form of spina bifida that
occurs when the spinal canal and backbone do not close before birth, causing
the spinal cord to protrude through an opening in the back. This can cause
partial or complete paralysis below the spinal opening. Type III includes
a form of dysraphism with a portion of the cerebellum and/or brainstem
pushing out through a defect in the back of the head or neck. Type III
is very rare the most serious form of CM. It is associated with an early
high mortality rate, or severe neurological deficits in patients that
survive. Type IV is the most severe and rarest form of CM. In Type IV,
the cerebellum fails to develop normally. There may be other associated
malformations of the brain and brainstem. Most babies born with this malformation
do not survive infancy.
There are different causes of Chiari Malformation. The most common is Primary
CM which is caused by structural defects in the brain and spinal cord
that occur during fetal development, whether caused by genetic mutations
or lack of proper vitamins or nutrients in the mother's diet. Secondary
CM can be caused later in life if spinal fluid is drained excessively
from the lumbar or thoracic areas of the spine due to injury, infection
or exposure to harmful substances.
Many people with Type I Chiari Malformation will have no symptoms and the
condition may be discovered while doing other tests. If patients do have
symptoms they may consists of any one or combination of the following:
- Severe head and neck pain
- Occipital headache felt at the base of the skull that is made worse by
coughing, sneezing, etc.
- Loss of pain and temperature sensation of upper torso and arms
- Loss of muscle strength in the hands and arms
- Drop attacks (collapsing to the ground due to muscle weakness)
- Blurred Vision
- Balance Problems
- Sensitivity to bright lights
This type of malformation is characterized by downward displacement of
the medulla, fourth ventricle, and cerebellum into the cervical spinal
canal. This type occurs almost exclusively with patients with myelomeningocele
(a form of spina bifida). Symptoms may include:
- Changed pattern of breathing, including periods of apnea
- Depressed gag reflex
- Involuntary, rapid, downward eye movements
- Loss of arm strength.
This type of malformation includes a form of spinal dysraphism with a portion
of the cerebellum and/or brainstem pushing out through a defect in the
back of the head and neck. Early operative closure of the defect is necessitated.
Shunting is necessary to treat hydrocephalus which is commonly present.
Additional severe birth defects are often present and will require extensive
Because many people with CMs have no symptoms and their condition is discovered
through coincidence, the physician will perform a physical exam and check
memory, balance, cognition, touch, reflexes, sensations. One of the following
may also be ordered.