Chiari malformation
noun
Chi·ari malformation
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Medical Definition of Chiari malformation
: a congenital abnormality of the hindbrain in which the cerebellum and often parts of the brain stem protrude into the spinal canal through the foramen magnum
Blocked spinal fluid can cause hydrocephalus or, as is more common in Chiari malformation, a fluid-filled cyst known as a syrinx.— Rebecca Voelker, The Journal of the American Medical Association, 14 Jan. 2009
Note: Chiari malformation is usually classified into four types. Type 1 involves protrusion only of the lower part of the cerebellum into the spinal canal and is often asymptomatic. Type 2 is the Arnold-Chiari malformation. In type 3, the cerebellum is completely displaced into the spinal canal. In type 4, the cerebellum fails to develop completely.