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