Chiari Malformation
Chiari malformation is a rare abnormality at the base of the brain that results in brain tissue extending into the spinal canal. The condition may be present at birth (congenital). Medical experts divide Chiari malformation into several types, in part to reflect the degree of displacement of the brain tissue into the spinal canal. The most common are Chiari-I and Chiari-II.
In Chiari-I malformation, brain tissue (the cerebellum tonsils — two pegs of tissue which hang off the cerebellum at the base of the brain) protrudes below the opening of the base of the skull (foramen magnum). It may also include displacement of the lower part of the brain (medulla). Chiari-I malformation usually causes symptoms in young adults and is often associated with syringomyelia (a tubular, fluid-filled cavity within the spinal cord) and abnormalities in the bones of the skull and/or spine.
Chiari-II malformation involves a greater degree of brain tissue protruding into the spinal canal. In addition to the cerebellum tonsils, Chiari-II also includes the medulla and a cavity of the brain (fourth ventricle). Chiari-II malformation is almost always associated with myelomeningocele (a type of spina bifida) and hydrocephalus (excess fluid buildup within the brain), which usually are apparent at birth. Onset in adulthood is rare.
Chiari-III and Chiari-IV malformation are rare and are apparent at birth. They are more severe and are part of a larger syndrome seen in children with spina bifida. In Chiari-III, the back of the brain protrudes from an opening in the back of the skull area. It is part of a more severe set of birth defects, requiring extensive treatment. Infants with this form of Chiari malformation may have life-threatening complications.
Chiari-IV is the most severe form; the back of the brain fails to develop normally. Most infants with this malformation do not survive infancy.
Some symptoms of Chiari malformation may be subtle and can erroneously be attributed to similar symptoms of unrelated chronic conditions.
Many people with the Chiari I Malformation experience no symptoms. When symptoms are present, they usually do not appear until adolescence or early adulthood, but can occasionally be seen in young children. The majority of patients complain of severe head and neck pain. Headaches are often accentuated by coughing, sneezing or straining. Patients may complain of dizziness, vertigo, disequilibrium, muscle weakness or balance problems. Often fine motor skills and hand coordination will be affected.
Vision problems can also occur. Some patients experience blurred or double vision, difficulty in tracking objects or a hypersensitivity to bright lights. Physical examination may reveal nystagmus (involuntary eye movements). Other symptoms include tinnitus (buzzing or ringing in the ear), hearing loss or vocal cord paralysis. Patients may have difficulty swallowing, frequent gagging and choking and, in some cases, sleep apnea may be present.
The Chiari I Malformations may also be associated with other disorders such as hydrocephalus (build up of fluid in the ventricles of the brain) or Syringomyelia. Syringomyelia is a disorder in which cerebrospinal fluid enters the spinal cord, forming a cavity known as a syrinx. It is recommended that patients diagnosed with a Chiari Malformation have the entire spine imaged to rule out the presence of a syrinx, since it may be a consideration in treatment and prognosis.
In addition to a thorough physical and neurologic examination, and an extensive patient history, the most definitive test used to diagnose Chiari malformation is magnetic resonance imaging (MRI) of the skull. Physicians can accurately view the cerebellum and surrounding structures and determine what form and to what extent the malformation has progressed.
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