A Chiari malformation type I involves ectopia of cerebellar tonsils through the foramen magnum into the spinal canal. It can be diagnosed based on findings seen on imaging studies.

Criteria for Chiari Type I - one of the following:

(1) >= 5 mm caudal descent of the cerebellar tonsils

(2) >= 3 mm caudal descent of the cerebellar tonsils AND >= 1 indicator of crowding in the subarachnoid space in the area of the cranio-cervical junction



• The level of the foramen magnum was defined as the line extending from the inferior limit of the basion to the ophistion.



(1) other malformations of the central nervous system

(2) secondary herniation of the cerebellar tonsils due to intracranial hypertension or severe trauma

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