Arnold-Chiari syndrome
Arnold-Chiari syndrome, also known as Arnold-Chiari malformation, involves a defect in the formation of the cerebellum and brainstem, which may obstruct the flow of blood from the brain into the spinal canal. It is typically associated with myelomeningocele, a serious form of spina bifida, and is categorized into four types based on severity, with Type II commonly linked to spina bifida. The condition is believed to arise from structural defects during fetal development, and genetic factors may play a role in its occurrence, as it has been observed to run in families. Symptoms can range from severe issues in infants, such as vomiting and paralysis, to milder manifestations in adolescents like headaches and coordination problems. Diagnosis generally involves a thorough medical history review, physical examination, and imaging studies such as MRI or CT scans. Treatment often requires surgical intervention to relieve obstructions, along with therapies that may improve coordination and daily functioning. While there is currently no known way to prevent Arnold-Chiari syndrome, genetic counseling may be beneficial for affected families. Understanding and awareness of this condition can support affected individuals and their families in managing its complexities.
Arnold-Chiari syndrome
ALSO KNOWN AS: Arnold-Chiari malformation; type II Chiari malformation; cerebellomedullary malformation syndrome
DEFINITION Arnold-Chiari syndrome is a defect in the formation of the cerebellum (the small, bottom portion of the brain) and brainstem. This defect can prevent the passage of blood from the brain into the spinal canal. Arnold-Chiari syndrome is usually accompanied by a myelomeningocele, which is a form of spina bifida. There are four types of Arnold-Chiari syndrome, numbered according to the degree of severity. Type 2 is associated with spina bifida.
Risk Factors
Spina bifida and hydrocephalus are commonly associated with Arnold-Chiari syndrome but are not thought to be a cause of the disorder.
Etiology and Genetics
Primary Arnold-Chiari malformations typically result from structural defects in the spinal cord and brain which occur during fetal development. There has been suspicion for many years that this malformation results at least in part from a genetic defect because medical literature has reported about several families in which more than one family member is affected. A 2006 study by A. L. Boyle et al., published in the American Journal of Medical Genetics, Part A, analyzed 10,000 single-nucleotide polymorphisms (SNPs) and identified candidate genes on chromosome 9 and 15 for further study. As of 2024, research into the heritability of Arnold-Chiari had discovered that Arnold-Chiari was genetic in nature, meaning that there is an increase in risk for the disorder to run in families. However, the specific genetic mechanism that causes Arnold-Chiari remained undiscovered.
Some researchers have suggested that the developmental trigger is a lack of particular vitamins or specific nutrients in the maternal diet. Others suggest that since the base of a patient’s skull is often quite small, resulting in the cerebellum being forced downward, the genes regulating this aspect of skull development must be involved. A third group suggests that the primary cause is the overgrowth of the cerebellum, and that genes involved with cerebellar development are responsible. It is likely that many genes play small contributing roles and that these, along with other significant environmental or developmental factors, all combine to induce the development of the malformation.
Symptoms
Symptoms exhibited in infants may include vomiting, mental impairment, weakness, and paralysis of the limbs. Symptoms in adolescents are usually milder and may include headaches, dizziness, fainting, weakness of the legs, double vision, and deafness. Other adolescent symptoms may include swelling of the optic nerve region, rapid eye movement (nystagmus), lack of muscular coordination, uncontrolled shaking or trembling, walking problems, and numbness or tingling in the extremities. Some affected persons also have a syringomyelia (a spinal cyst or cavity).
Screening and Diagnosis
The doctor will ask about a patient’s symptoms and medical history and will perform a physical exam. The doctor may also perform a magnetic resonance imaging (MRI) scan and/or a computed tomography (CT) scan to view the inside of the brain.
Cerebrospinal fluid (CSF) is a vital fluid that surrounds the brain and spine. Special studies to evaluate the flow of CSF may be performed.
Treatment and Therapy
Patients should discuss the best plans with their doctors. Among the treatment options, surgery is usually required to correct any obstruction in the brain.
Depending on the symptoms associated with Arnold-Chiari syndrome, other treatments may be beneficial. For example, physical or occupational therapy may help improve muscular coordination and trembling. Braces or a wheelchair may be needed. Speech therapy may also be beneficial.
Prevention and Outcomes
There is no known way to prevent Arnold-Chiari syndrome. Parents of a child with this condition may benefit from genetic counseling.
Bibliography
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Chen, Harold. “Chiari Malformation.” Atlas of Genetic Diagnosis and Counseling. 2nd ed. New York: Springer, 2012. Digital file.
"Chiari Malformation." Mayo Clinic, 20 Oct. 2023, www.mayoclinic.org/diseases-conditions/chiari-malformation/symptoms-causes/syc-20354010. Accessed 9 Sept. 2024.
"Chiari Malformation Fact Sheet." National Institute of Neurological Disorders and Stroke. National Institutes of Health, US Dept. of Health and Human Services, 16 Apr. 2014. Web. 14 July 2014.
Kumar, Praveen, and Barbara K. Burton, eds. “Chiari Malformations.” Congenital Malformations: Evidence-Based Evaluation and Management. New York: McGraw-Hill Medical, 2008. Print.
McCoy, Krisha. "Arnold-Chiari Syndrome." Health Library. EBSCO, 12 Feb. 2014. Web. 14 July. 2014.
NORD. "Chiari Malformations." RareDiseases.org. National Organization for Rare Disorders, 2014. Web. 21 July 2014.
Rubin, Jonathan M., and William F. Chandler. Ultrasound in Neurosurgery. New York: Raven, 1990. Print.
Viana, G. M., et al. “Association of HTLV-I with Arnold Chiari Syndrome and Syringomyelia.” Brazilian Journal of Infectious Diseases12.6 (2008): 536–37. Print.