Cerebellum

The cerebellum, meaning "the little brain", sits at the base of the brain in the posterior cranial fossa below the tentorium and behind the brainstem. 

Gross anatomy

The cerebellum has the following features:

• three surfaces: anterior (petrosal), superior (tentorial), inferior (suboccipital)
• three fissures: primary (tentorial), horizontal (petrosal), prebiventral/prepyramidal (suboccipital)
• two hemispheres
• single median vermis

Vermis

The cerebellar vermis is located in the midline, separating the two cerebellar hemispheres. Its organization mirrors that of the adjacent hemispheres divided into nine lobules.

Cerebellar hemisphere

Just like the vermis, each hemisphere is divided into nine lobules separated by fissures:

1. wing of lingula (lingula)
2. wing of central lobule (central lobule)
3. quadrangular lobule (culmen)
   • primary (tentorial) fissure
4. simple lobule (declive)
5. superior semilunar lobule (folium)
   • horizontal (petrosal) fissure
6. inferior semilunar lobule (tuber)
   • prebiventral/prepyramidal (suboccipital) fissure
7. biventral lobule (pyramid)
8. tonsil (uvula)
9. flocculus (nodulus)

Connections to brainstem

• to the midbrain via the superior cerebellar peduncles (brachia conjunctiva)
• to the pons via the middle cerebellar peduncles (brachia pontis)
• to the medulla via the inferior cerebellar peduncles (restiform bodies)

CSF cisterns

• cerebellopontine angle cistern
• cisterna magna
• quadrigeminal cistern

Arterial supply

The cerebellum is supplied by three bilateral arteries from the vertebrobasilar system:

1. superior cerebellar artery (SCA): branch of the distal basilar artery
2. anterior inferior cerebellar (AICA): branch of the proximal basilar artery
3. posterior inferior cerebellar (PICA): branch of the distal vertebral arteries

Superior cerebellar (SCA)

The SCA supplies:

• whole superior surface of the cerebellar hemispheres down to the great horizontal fissure
• the superior vermis
• dentate nucleus
• most of the cerebellar white matter
• superior cerebellar peduncle
• middle cerebellar peduncle

Anterior inferior cerebellar (AICA)

The AICA has a variable vascular territory depending on the size of the PICA (see AICA-PICA dominance) but usually supplies:

• middle cerebellar peduncle
• inferolateral portion of the pons
• flocculus
• anteroinferior surface of the cerebellum

Posterior inferior cerebellar (PICA)

The PICA has a variable vascular territory depending on the size of the AICA (see AICA-PICA dominance), but usually supplies:

• posteroinferior cerebellar hemispheres (up to the great horizontal fissure)
• inferior portion of the vermis
• inferior cerebellar peduncle

It divides into lateral and medial branches that supply the inferior portion of the vermis and cerebellar hemispheres respectively.

There are some variations in the PICA:

• 18% arise extracranially, inferior to the foramen magnum
• 10% arise from the basilar rather than vertebral artery
• 2% bilaterally absent
• occasionally loops around the cerebellar tonsil
• occasionally a small vertebral artery will terminate into a common PICA/AICA trunk

Venous drainage

There are three major groups of bilateral veins that drain the cerebellum along with other structures of the posterior cranial fossa. Not unsurprisingly there is significant variation between patients and also between the left and right in the same patient.

The three posterior fossa venous groups are:

• superior (Galenic)
  • drains the midbrain, upper pons, superior vermis and the superior surface of the cerebellar hemispheres
  • drains into the vein of Galen and has three named veins
    • precentral cerebellar vein
    • superior vermian vein
    • anterior pontomesencephalic vein
• anterior (petrosal)
  • drains the lateral pons, medulla and the anterior surface of the cerebellar hemispheres
  • drains into the inferior petrosal sinus and has a petrosal vein
• posterior (tentorial)
  • drains the inferior vermis, tonsils and the posteroinferior surface of the cerebellar hemispheres
  • drains into the transverse sinus  and has an inferior vermian vein

Variant anatomy

• cerebellar agenesis
• tonsillar ectopia: asymptomatic protrusion of the tonsils through the foramen magnum by no more than 3-5 mm

Related pathology

• neoplastic
  • Lhermitte-Duclos disease
• inflammatory
  • acute cerebellitis 
• degenerative
  • diffuse cerebellar atrophy
  • crossed cerebellar atrophy
• congenital disease
  • cerebellar hypoplasia
  • rhombencephalosynapsis
• intoxication
  • CHANTER syndrome
• signs
  • dense cerebellum sign
  • zebra sign
• others
  • cerebrotendinous xanthomatosis
  • cerebellar hemorrhage
  • crossed cerebellar diaschisis
  • remote cerebellar hemorrhage