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.

wing of lingula (lingula)
wing of central lobule (central lobule)
quadrangular lobule (culmen)
- primary (tentorial) fissure
simple lobule (declive)
superior semilunar lobule (folium)
- horizontal (petrosal) fissure
inferior semilunar lobule (tuber)
- prebiventral/prepyramidal (suboccipital) fissure
biventral lobule (pyramid)
tonsil (uvula)
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

Arterial supply

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

superior cerebellar artery (SCA): branch of the distal basilar artery
anterior inferior cerebellar (AICA): branch of the proximal basilar artery
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