The cerebellar tonsil (Latin: tonsilla cerebelli) is a rounded lobule on the undersurface of each
cerebellar hemisphere, continuous medially with the
uvula
The palatine uvula, usually referred to as simply the uvula, 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 fibers. It also conta ...
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 fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior su ...
and superiorly by the
flocculonodular lobe
The flocculonodular lobe (vestibulocerebellum) is a lobe of the cerebellum consisting of the nodule and the flocculus. The two flocculi are connected to the midline structure called the nodulus by thin pedicles. It is placed on the anteroinferio ...
. 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 of the skull resulting in
tonsillar herniation
Brain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the brain is squeezed across structures within the skull. The brain can shift across such structures as the falx cerebri, the te ...
. 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
Chiari malformation
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 cause headaches, difficu ...
.
Pathology
A
Type I Chiari malformation
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 cause headaches, difficu ...
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
Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.
CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...
(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
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