|Brain: Cerebellar tonsil|
|Under surface of the cerebellum. (Tonsil visible at center right.)|
|Sagittal section of the cerebellum, near the junction of the vermis with the hemisphere. (Tonsil visible at bottom center.)|
|Gray's||subject #187 791|
The cerebellar tonsil (amygdaline nucleus) is a rounded mass, situated in the hemispheres of the cerebellum.
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).