Origin and Course
The artery originates from the intradural (intracranial) segment of the vertebral artery (a. vertebralis). Its point of origin lies just distal to the point where the vertebral artery penetrates the subarachnoid space, immediately before the two vertebral arteries unite to form the single basilar artery.
From there, the vessel courses toward the inferior surface of the cerebellum, forming numerous anastomoses along its path with other arteries supplying cerebellar structures.
Branches of the PICA
Along its course, the artery gives off several important branches to structures of the posterior cranial fossa:
- Choroid branch of the fourth ventricle (r. choroideus ventriculi quarti) — supplies the choroid plexus of the IV ventricle.
- Lateral and medial medullary branches (rr. medullares laterales et mediales) — supply the medulla oblongata.
- Tonsillar branch of the cerebellum (r. tonsillae cerebelli) — supplies the cerebellar tonsil.
What Does the PICA Supply?
Its vascularization zone encompasses both cerebellar structures and the brainstem.
In the cerebellum, the artery supplies:
- The basal part of the cerebellar hemispheres.
- The inferior vermis.
- Part of the deep cerebellar nuclei.
In the brainstem, the artery supplies:
- The dorsolateral (retro-olivary) region of the medulla oblongata. This area includes the inferior cerebellar peduncle and the spinal trigeminal tract.
Variant Anatomy and Hemodynamic Balance
Cerebellar arteries are characterized by marked asymmetry and interchangeability. The size and vascularization territory of the PICA are inversely related to the territory of the anterior inferior cerebellar artery (a. cerebelli inferior anterior).
If the PICA is of small caliber on one side, the blood flow deficit in the basal cerebellum is compensated by the ipsilateral anterior inferior cerebellar artery or by a larger contralateral PICA.
In congenital hypoplasia (underdevelopment) of the vertebral artery, it may fail to participate in the formation of the basilar artery and continue exclusively as the PICA.
Clinical Significance
The topographical features of the artery are of great clinical importance:
- Aneurysms: Approximately 3% of all intracranial saccular aneurysms occur at the junction of the vertebral artery and the PICA. Due to the vessel's location, the rupture of such an aneurysm leads to bleeding directly into the subarachnoid space (SAH).
Do Not Confuse: Pica chlorotica
The abbreviation PICA refers to the posterior inferior cerebellar artery. However, medicine also features the Latin term Pica chlorotica, which has no relation to vascular anatomy. This refers to pica: an eating disorder characterized by a craving for chalk, coal, and other non-nutritive substances, which is a sign of sideropenic syndrome in iron deficiency anemia.