Cerebellar tonsils

The cerebellar tonsil (amygdaline nucleus) is a rounded mass, situated in the hemispheres of the cerebellum.

Pathology
Arnold-Chiari malformation is a congenital anomaly of the brain in which the cerebellar tonsils are elongated and pushed down through the opening of the base of the skull (see foramen magnum), blocking the flow of cerebrospinal fluid (CSF).