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.

Two lobes that make up the lowest part of the cerebellum; one at the bottom of each hemisphere. (Many doctors claim that the cerebellar tonsils have no function of their own, however damage to either or both have been known to produce symptoms including: dizziness, unsteady gait, poor depth perception, sensations of swaying/floating, nausea or vomiting, fatigue, brain fog, insomnia, loss of memory, aphasia, and becoming easily confused.)


A method of Magnetic Resonance Imaging (MRI) that allows for scanning of the patients in the positions they experience their problems— standing, bending, sitting, leaning, as well as the standard lying down. With Chiari this can be an invaluable tool, much better than the standard supine (horizontal) MRI, because it allows images that include the effects gravity is having on herniation (tonsillar ectopia). Additionally, it can make certain comorbid conditions, such as Tethered Cord, more visible.