A Chiari malformation (sometimes called an Arnold Chiari) is a neurological disorder where part of the brain, the cerebellum (or more specifically the cerebellar tonsils), descends out of the skull into the spinal area. Chiari malformations affect females more often than males. These defects develop during fetal development. Much less commonly, Chiari malformations can occur later in life. This can happen when an excessive amount of cerebrospinal fluid is drained away because of injury, infection, exposure to toxic substances.
A Chiari malformation can also cause pressure on the brain and produce hydrocephalus (pressure due to excessive cerebrospinal fluid accumulation in the brain) and the spinal cord, potentially causing a wide variety of symptoms.
Signs & Symptoms
Children with Chiari I malformations may start to have symptoms as early as age 2 or 3. Some don't have any symptoms until they are older. The signs and symptoms of Chiari malformation can vary greatly from one person to another. Symptoms may go through periods of exacerbation and remission. Specific symptoms can occur in different combinations and generally reflect dysfunction of the cerebellum, the brainstem, the spinal cord and lower cranial nerves.
Chiari malformation is diagnosed by MRI (Magnetic Resonance Imaging). This test is to detect brain stem and spinal cord compression. An MRI (Magnetic Resonance Imaging - a non-invasive test which uses a large magnet to create a picture of internal organs) can clearly show if the cerebellar tonsils are out of position. Unfortunately, there is no single, objective test which can clearly say that someone has a Chiari malformation which is causing problems. The diagnosis of a Chiari II malformation can be made prenatally through ultrasound.
The prognosis differs dependent on the type of malformation (i.e., type I, II, III, or IV). Type I is generally adult-onset and, while not curable, treatable and rarely fatal.Syndrome of Occipitoatlantoaxial Hypermobility (Ehlers-Danlos syndrome related) is more difficult to treat than the congenital form of the disease. Individuals with this type do not respond well to the decompression surgery and often require an occipitoatlantoaxial fusion for stability.These patients are at risk of experiencing serious heart complications. Types I and II sufferers may also develop syringomyelia. Type II is typically diagnosed at birth or prenatally.Approximately 33% of individuals with Chiari II malformation develop symptoms of brainstem damage within five years; a 1996 study found a mortality rate of 33% or more among symptomatic patients, with death frequently occurring due to respiratory failure.15% of individuals with Chiari II malformation die within two years of birth. Among children under two who also have myelomeningocele, it is the leading cause of death. Prognosis among children with Chiari II malformation who do not have spina bifida is linked to specific symptoms; the condition may be fatal among symptomatic children when it leads to neurological deterioration, but surgical intervention has shown promise.Types III and IV are extremely rare and patients generally do not survive past the age of two or three.