cerebellar tonsillar herniation

https://doi.org/10.1351/goldbook.11668
Abnormal protrusion of a portion of the cerebellum through the foramen magnum of the skull.
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 855 [Terms] [Paper]