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    Chiari Malformations

    Important
    It is possible that the main title of the report Chiari Malformations is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

    Synonyms

    Disorder Subdivisions

    • None

    General Discussion

    Summary
    Chiari malformations are a group of complex brain abnormalities that affect the area in lower posterior skull where the brain and spinal cord connect. The underlying anatomy of Chiari malformations is thought to be present at birth (congenital), although in many cases they may not become clinically apparent until adulthood. In extremely rare cases, a Chiari malformation may be acquired during life. The exact cause of Chiari malformations are not known, but often the cavity near the base of the skull (posterior fossa) is narrow and abnormally small in relation to the size of the cerebellum, which this portion of the skull encloses. Researchers believe that in some cases the small posterior fossa may cause the developing brain, specifically the cerebellum and the brainstem, to be pushed downward. Part of the cerebellum (known as the cerebellar tonsils) may protrude (herniate) through the foramen magnum, which is the normal opening found in the occipital bone at the base of the skull. The tonsils may thus interfere with the flow of cerebrospinal fluid (CSF) to and from the skull and spinal canal, potentially leading to accumulation of cerebral spinal fluid in the subarachnoid spaces of the brain and spine. 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. In fact, no two cases of Chiari malformation are exactly alike and the associated symptoms are highly variable. The severity of Chiari malformations can vary dramatically as well. In some cases, affected individuals may not develop any symptoms (asymptomatic); in others, severe, potentially debilitating or life-threatening symptoms can develop.

    Traditionally, Chiari malformations have been defined and classified by how much of the cerebellar tonsils protrude through the foramen magnum. A diagnosis of a Chiari malformation usually signifies that the cerebellar tonsils protrude below the foramen magnum (often cited as at least 5 millimeters, though this is controversial). However, researchers have determined that the length of tonsil descent in a Chiari malformation does not always correspond to the severity of symptoms or to the response to treatment. In fact, some individuals are classified as having Chiari malformation type 0, in which there is minimal or no descent of the cerebellar tonsils. These individuals still have symptoms associated with a Chiari malformation, most likely due to abnormalities in the flow of cerebrospinal fluid within the skull and spinal canal. Research is ongoing to understand the complex, underlying mechanisms that cause Chiari malformations.

    Introduction
    Chiari malformations are named for Hans Chiari, an Austrian pathologist, who first identified type I-III in 1891. Julius Arnold further expanded the definition of Chiari malformation type II and some medical sources began using the name Arnold-Chiari malformation. Nowadays, some medical sources use Arnold-Chiari malformation as a broad term for all forms. Chiari malformations have also been known as congenital tonsillar herniation, tonsillar ectopia or tonsillar descent.

    Resources

    American Syringomyelia & Chiari Alliance Project
    P.O. Box 1586
    Longview, TX 75606-1586
    Tel: (903)236-7079
    Fax: (903)757-7456
    Tel: (800)272-7282
    Email: info@asap.org
    Internet: http://www.asap.org

    March of Dimes Birth Defects Foundation
    1275 Mamaroneck Avenue
    White Plains, NY 10605
    Tel: (914)997-4488
    Fax: (914)997-4763
    Tel: (888)663-4637
    Email: Askus@marchofdimes.com
    Internet: http://www.marchofdimes.com

    Spina Bifida Association of America
    4590 MacArthur Boulevard NW
    Suite 250
    Washington, DC 20007-4226
    Tel: (202)944-3285
    Fax: (202)944-3295
    Tel: (800)621-3141
    Email: sbaa@sbaa.org
    Internet: http://www.sbaa.org

    Hydrocephalus Association
    4340 East West Highway Ste 950
    Bethesda, MD 20814
    USA
    Tel: (301)202-3811
    Fax: (301)202-3813
    Tel: (888)598-3789
    Email: info@hydroassoc.org
    Internet: http://www.hydroassoc.org

    NIH/National Institute of Neurological Disorders and Stroke
    P.O. Box 5801
    Bethesda, MD 20824
    Tel: (301)496-5751
    Fax: (301)402-2186
    Tel: (800)352-9424
    TDD: (301)468-5981
    Internet: http://www.ninds.nih.gov/

    Canadian Syringomyelia Network
    69 Penny Crescent
    Markham
    Ontario, L3P 5X7
    Canada
    Tel: 9054718278
    Fax: 9059444844
    Email: barb@csn.ca
    Internet: http://www.csn.ca/

    Hydrocephalus Support Group, Inc.
    1933 Mistflower Glen Ct.
    Chesterfield, MO 63005-4236
    USA
    Tel: (636)532-8228
    Fax: (314)251-5871
    Email: hydrob@earthlink.net

    Birth Defect Research for Children, Inc.
    976 Lake Baldwin Lane
    Orlando, FL 32814
    USA
    Tel: (407)895-0802
    Email: staff@birthdefects.org
    Internet: http://www.birthdefects.org

    World Arnold Chiari Malformation Association
    31 Newtown Woods Road
    Newtown Square, PA 19073
    Tel: (610)353-4737
    Email: chiari-owner@yahoogroups.com
    Internet: http://www.wacma.com

    Christopher S. Burton Syringomyelia Foundation, Inc.
    P.O. Box 100335
    Fort Lauderdale, FL 33310-0335
    Tel: (954)727-5137
    Fax: (954)636-2409
    Email: info@thesmfoundation.org
    Internet: http://www.thesmfoundation.org

    Conquer Chiari
    320 Osprey Court
    Wexford, PA 15090
    USA
    Tel: (724)940-0116
    Fax: (724)940-0172
    Email: director@conquerchiari.org
    Internet: http://www.conquerchiari.org

    Chiari & Syringomyelia Foundation
    29 Crest Loop
    Melville, NY 11747
    Tel: (718)966-2593
    Internet: http://www.CSFinfo.org

    For a Complete Report:

    This is an abstract of a report from the National Organization for Rare Disorders (NORD). A copy of the complete report can be downloaded free from the NORD website for registered users. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational therapies (if available), and references from medical literature. For a full-text version of this topic, go to www.rarediseases.org and click on Rare Disease Database under "Rare Disease Information".

    The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only. NORD recommends that affected individuals seek the advice or counsel of their own personal physicians.

    It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report

    This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

    For additional information and assistance about rare disorders, please contact the National Organization for Rare Disorders at P.O. Box 1968, Danbury, CT 06813-1968; phone (203) 744-0100; web site www.rarediseases.org or email orphan@rarediseases.org

    Last Updated: 3/5/2014
    Copyright 1986, 1995, 2002, 2005, 2011, 2014 National Organization for Rare Disorders, Inc.

    WebMD Medical Reference from the National Organization for Rare Disorders

    Last Updated: May 28, 2015
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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