Medical Definition of Arnold-Chiari malformation
: a congenital abnormality in which the lower surface of the cerebellum and the lower brain stem protrude into the spinal canal through the foramen magnum She was born with Arnold-Chiari malformation, a rare and random birth defect that occurs, according to one study, in about 8 of 100,000 people. A deformity of the base of the skull and spine, it can cause chronic pain and loss of balance.— Arthur Allen, The Washington Post, 23 Feb. 1997
Note: Arnold-Chiari malformation often occurs with spina bifida and hydrocephalus. It is classified as a type of Chiari malformation.
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