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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 cerebral artery.

Territory

Has a variable territory depending on the size of the AICA. Typically it may supply:

  • posteroinferior cerebellar hemispheres (up to the great horizontal fissure)
    • cerebellar tonsils: 85% of the time
    • biventral lobule: 80%
    • neucleus gracilis: 85%
    • superior semilunar lobule: 50%
  • inferior portion of the vermis
  • lower part of the medulla: 50%

Origin

Its origin is also variable:

  • 18-20% 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 segment
    • from its origin around the inferior aspect of the medullary olive
  • 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 tonsilar position.
    • the apex of the loop is
      • above foramen magnum in 60% of cases
      • at the level of FM in 10%
      • and below in 30%
      • Its relationship to the vertebral artery is also variable, 84% lateral and 16% medial
  • posterior medullary segment
    • ascends posterior to the medulla behind CN IX and CN X and along the posterior medullary velum.
  • 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: it is known as the "choroid point". This point has a constant relationship with the 4th ventricle and was used prior to crossectional imaging to asses for shift in its position.

Branches

  • anterior and lateral medullary segments
    • small perforating medullary branches (absent in 50%)
  • supratonsillar segment
    • tonsillohemispheric branch
    • inferior vermian branch

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

See also


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Neuroanatomy

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