The cerebellar tonsil (Latin: tonsilla cerebelli) is a paired rounded lobule on the undersurface of each

cerebellar hemisphere The cerebellum consists of three parts, a median and two lateral, which are continuous with each other, and are substantially the same in structure. The median portion is constricted, and is called the vermis, from its annulated appearance which ...

, continuous medially with the

uvula The uvula (: uvulas or uvulae), also known as the palatine uvula or staphyle, is a conic projection from the back edge of the middle of the soft palate, composed of connective tissue containing a number of racemose glands, and some muscular fi ...

of the

cerebellar vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior cranial fossa, posterior fossa of the cranium. The primary fissure in the vermis curves ventrolatera ...

and superiorly by the

flocculonodular lobe The flocculonodular lobe ( vestibulocerebellum) is one of the lobes of the cerebellum. It is a small lobe consisting of the unpaired midline nodule and the two flocculi: one flocculus on either side of the nodule. The lobe is involved in maintai ...

. Synonyms include: tonsilla cerebelli, amygdala cerebelli, the latter of which is not to be confused with the cerebral tonsils or amygdala nuclei located deep within the medial temporal lobes of the cerebral cortex. 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. Elongation of the cerebellar tonsils can, due to pressure, lead to this portion of the cerebellum to slip or be pushed through the

foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

of the skull resulting in tonsillar herniation. This is a life-threatening condition as it causes increased pressure on the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

which contains respiratory and cardiac control centres. A congenital condition of tonsillar herniation of either one or both tonsils is

Chiari malformation In neurology, the Chiari malformation ( ; CM) is a structural defect in the cerebellum, characterized by a downward displacement of one or both cerebellar tonsils through the foramen magnum (the opening at the base of the skull). CMs can cau ...

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 (see

), blocking the flow of

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

(CSF) as it exits through the medial and lateral apertures of the fourth ventricle. Also called cerebellar tonsillar ectopia, or tonsillar herniation. Although often congenital, Chiari malformation symptoms can also be induced due to physical head trauma, commonly from raised intracranial pressure secondary to a hematoma, or increased dural strain pulling the brain caudally into the foramen magnum. Head trauma increases risk of cerebellar tonsillar ectopia by a factor of 4. Ectopia may be present but asymptomatic until whiplash causes it to become symptomatic.

Additional images

File:Human cerebellum anterior view description.JPG, Human cerebellum anterior view File:Human brain midsagittal view description.JPG, Human brain midsagittal view File:Slide2SEER.JPG, Cerebellum. Inferior surface. File:Slide3EER.JPG, Cerebellum. Inferior surface. File:Slide4SER.JPG, Cerebellum. Inferior surface.

References

Cerebellum {{neuroanatomy-stub