Cerebellar tonsil

The flocculonodular lobe of the cerebellum, which can also be confused for the cerebellar tonsils, is one of three lobes that make up the overall composition of the cerebellum. The cerebellum consists of three anatomical and functional lobes: anterior lobe, posterior lobe, and flocculonodular lobe.

The cerebellar tonsil is part of the posterior lobe, also known as the neocerebellum, which is responsible for coordinating the voluntary movement of the distal parts of limbs.

Due to increased intracranial pressure, cerebellar tonsil can slip or be pushed through the foramen magnum of the skull resulting in tonsillar herniation. This is a life-threatening condition as it causes increased pressure on the medulla oblongata which contains respiratory and cardiac control centres. A congenital condition of tonsillar herniation of either one or both tonsils is called Chiari malformation.

Pathology

A Type I 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, potentially affecting the flow of cerebrospinal fluid as it exits through the medial and lateral apertures of the fourth ventricle.