Dislocation of the cerebellar tonsils, downward out of the skull; usually measured in mm (millimeters) or cm (centimeters).

  • What originally distinguished a tonsillar ectopia from a Chiari Malformation rested solely on the size of the herniation.
  • Since 3-5% of the population has some degree of tonsillar ectopia (without symptoms), a tonsillar ectopia was defined as being < 5mm and a CM was > 5mm. (The proper position of the tonsils should actually be 3mm above the foramen magnum.)
  • As studies have shown that size IS NOT the biggest factor in evaluating symptomology, they have moved away from this size based standard approach to diagnosing Chiari.
Cerebellar Herniation. Tonsillar Ectopia, tonsillar herniation


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