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Chiari Malformations

National Organization for Rare Disorders, Inc.

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

  • CM
  • Arnold-Chiari Malformation (ACM)

Disorder Subdivisions

  • Chiari type II (Chiari malformation II)
  • Chiari type III (Chiari malformation III)
  • Chiari type IV (Chiari malformation IV)
  • Chiari type 0 (Chiari malformation 0)
  • Chiari type I (Chiari malformation I)

General Discussion

Summary
Chiari malformations are a group of complex brain abnormalities that affect the area in lower back of the skull where the brain and spinal cord connect. Chiari malformations are thought to be present at birth (congenital), although in many cases they may not become 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 and the neck. The tonsils 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). 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 types 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
870 Market Street
Suite 955
San Francisco, CA 94102
USA
Tel: (415)732-7040
Fax: (415)732-7044
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
Email: me20t@nih.gov
Internet: http://www.ninds.nih.gov/

Canadian Syringomyelia Network
69 Penny Crescent
Markham
Ontario, L3P 5X7
Canada
Tel: (905) 471-8278
Fax: (905) 944-4844
Email: barb@csn.ca
Internet: http://www.csn.ca

Hydrocephalus Support Group, Inc.
P.O. Box 4236
Chesterfield, MO 63006-4236
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
Fax: (407)895-0824
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

American Association of Neurological Surgeons
5550 Meadowbrook Drive
Rolling Meadows, IL 60008-3852
Tel: (847)378-0500
Fax: (847)378-0600
Tel: (888)566-2267
Email: info@aans.org
Internet: http://www.NeurosurgeryToday.org and http://www.aans.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
290 Broadhollow Road, Suite 210E
Melville, NY 11747
Tel: (516)228-3565
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:  6/1/2011
Copyright  1986, 1995, 2002, 2005, 2011 National Organization for Rare Disorders, Inc.

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