Posterior inferior cerebellar artery (PICA) is one of the three vessels that provide arterial supply to the cerebellum. It is the most variable and tortuous cerebellar artery.

Gross anatomy

Origin

The PICA is a paired artery that originates from the vertebral artery V4 segment.

However, its origin is highly variable:

• ~20% arise extracranially, inferior to the foramen magnum

• 10% arise from the basilar rather than vertebral artery

• 2% bilaterally absent

• occasionally arises from a common origin with the anterior inferior cerebellar artery

Segments

The segmental anatomy was defined microsurgically by Lister et al. ^6,7:

1. anterior medullary (p1) segment

   • courses along the front of the medulla at the level of the inferior olive

2. lateral medullary (p2) segment

   • variably courses (ascending or descending) along the side of the medulla near or between the origins of the 9^th, 10^th, and 11^th cranial nerve roots

3. tonsillomedullary (p3; TM) segment

   • courses along the posterolateral surface of the medulla and inferior cerebellar tonsil

   • contains the caudal loop, a downward convex loop that mostly remain superior to the foramen magnum but occasionally extend below it

   • marks the transition between the proximal (medulla-supplying) and distal (cerebellum-supplying) parts of the posterior inferior cerebellar artery

4. telovelotonsillar (p4; TVT) segment

   • courses in the cleft between the tela choroidea, inferior medullary velum rostrally, and superior pole of the cerebellar tonsil caudally

   • contains the cranial loop, also known as the choroid point or choroid arch, an upward convex loop that has a constant relation to the 4^th ventricle and gives rise to choroidal arteries

5. cortical (p5) segment

   • supplies branches to the cerebellar surface

Branches

The main trunk of the posterior inferior cerebellar artery usually bifurcates somewhere along the margin of the cerebellar tonsil into

• medial trunk

  • supplies the vermis and adjacent hemisphere

• lateral trunk

  • supplies the tonsil and hemisphere

The posterior inferior cerebellar artery gives off the following arteries:

• perforating (medullary) arteries

• choroidal arteries

• cortical arteries

Note: occasionally, a small vertebral artery will terminate into a common AICA-PICA complex.

Supply

It has a variable territory depending on the size of the AICA (AICA-PICA dominance). Typically it supplies:

• posteroinferior cerebellar hemispheres (up to the great horizontal fissure)

  • cerebellar tonsils: 85% of the time

  • biventral lobule: 80%

  • nucleus gracilis: 85%

  • superior semilunar lobule: 50%

• inferior portion of the vermis

• lower part of the medulla: 50%

• inferior cerebellar peduncles

Variant anatomy

• course may loop around the cerebellar tonsil

• rarely a single unpaired PICA will supply the PICA territory bilaterally ⁸

Related pathology

• PICA infarct