Which arteries contribute to the posterior cerebral circulation: Middle Cerebral Artery (MCA), Anterior Cerebral Artery (ACA), Posterior Inferior Cerebellar Artery (PICA), Posterior Cerebral Artery (PCA), Superior Cerebellar Artery, or Basilar Artery?

Arteries Contributing to the Posterior Cerebral Circulation

The posterior cerebral circulation is comprised of the Posterior Inferior Cerebellar Artery (PICA), Posterior Cerebral Artery (PCA), Superior Cerebellar Artery, and Basilar Artery. The Middle Cerebral Artery (MCA) and Anterior Cerebral Artery (ACA) are not part of the posterior circulation.

Anatomy of the Posterior Circulation

The posterior circulation consists of the vertebrobasilar arterial system, which supplies blood to the posterior portions of the brain, including the brainstem, cerebellum, and occipital lobes. This system includes:

1. Vertebral Arteries:

   • Typically arise from the subclavian arteries (in about 5% of individuals, the left vertebral artery arises from the aortic arch) 1
   • Divided into four segments (V1-V4), with the first three being extracranial 1
   • Join to form the basilar artery

2. Basilar Artery:

   • Formed by the union of the two vertebral arteries 1
   • Supplies the pons and midbrain
   • Gives rise to several important branches

3. Posterior Inferior Cerebellar Artery (PICA):

   • Branch of the vertebral artery (V4 segment) 1
   • Supplies the inferior part of the cerebellum including:
     • Lobulus semilunaris inferior
     • Lobulus gracilis
     • Lobulus biventer
     • Tonsilla cerebelli
     • Parts of the vermis (clivus, tuber, pyramis, uvula, nodulus) 2
   • Also supplies portions of the medulla 1

4. Superior Cerebellar Artery:

   • Arises from the basilar artery 1, 2
   • Supplies:
     • Superior part of the cerebellum
     • Lobulus anterior
     • Lobulus simplex
     • Lobulus semilunaris superior
     • Parts of the vermis (lobulus centralis, culmen, clivus)
     • Dentate nucleus 2
   • Also supplies a small brainstem territory in the dorsal tegmentum and tectum of the upper pons 2

5. Posterior Cerebral Artery (PCA):

   • Terminal branch of the basilar artery 1
   • Supplies:
     • Occipital lobe
     • Medial and inferior temporal lobe
     • Thalamus
     • Midbrain 3

6. Anterior Inferior Cerebellar Artery (AICA) (not mentioned in the question but part of posterior circulation):

   • Arises from the basilar artery 2
   • Supplies:
     • Lateral territory of the lower pons
     • Middle cerebellar peduncle
     • Flocculus and neighboring cerebellar lobules 2

Important Clinical Considerations

1. Anatomical Variations:

   • In approximately 11% of hemispheres, the posterior cerebral artery is exclusively supplied by the internal carotid artery (fetal variant) 4
   • In 46% of hemispheres, the internal carotid artery might contribute to PCA territory via a patent posterior communicating artery 4
   • These variations are important because they mean that occipital lobe infarcts (traditionally attributed to vertebrobasilar disease) can sometimes be caused by carotid disease 4

2. Diagnostic Challenges:

   • Posterior circulation strokes account for approximately 20-25% of all ischemic strokes 5
   • Diagnosis can be challenging due to the wide range of often non-specific symptoms 5
   • Common prehospital stroke scales may not adequately represent signs and symptoms of posterior circulation stroke 5

3. Clinical Significance:

   • Vertebral artery atherosclerosis may be the causative basis for approximately 20% of posterior circulation strokes 1
   • Vertebrobasilar arterial stenosis is associated with multiple ischemic episodes and a higher risk of early recurrent stroke compared to carotid stenosis 1, 6

Summary

The posterior cerebral circulation consists of the vertebrobasilar system, including:

• Posterior Inferior Cerebellar Artery (PICA)
• Posterior Cerebral Artery (PCA)
• Superior Cerebellar Artery
• Basilar Artery

The Middle Cerebral Artery (MCA) and Anterior Cerebral Artery (ACA) are part of the anterior circulation, which arises from the internal carotid arteries.