posterior inferior cerebellar artery

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

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 loops around the cerebellar tonsil
Segments
  • anterior medullary (or proximal cisternal) segment
    • from its origin around the inferior aspect of the olive of the medulla
  • lateral medullary segment
    • curves forming the 'caudal loop' which is located anteroinferior to the tip of the cerebellar tonsil, but does not relate to the tonsillar position
    • the apex of the caudal loop is
      • above foramen magnum in 60% of cases
      • at the level of foramen magnum in 10%
      • and below the foramen in 30%
    • its relationship to the vertebral artery is also variable
      • 84% lateral
      • 16% medial
  • posterior medullary (or simple medullary) segment
  • supratonsillar segment
    • junction between the posterior medullary segment and the supratonsillar segment is upwardly convex and is the site of origin of small choroidal branches
      • known as the choroid point, choroid arch or cranial loop
      • this point has a constant relationship with the 4th ventricle and was used prior to cross-sectional imaging to assess for a shift in its position
  • Branches
    • anterior and lateral medullary segments
      • small perforating medullary branches (absent in 50%)
    • supratonsillar segment
      • tonsillohemispheric (lateral) branch
      • inferior vermian (median) branch

    Note: occasionally, a small vertebral will terminate into a common PICA/AICA trunk.

    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

    See also