Topics

Topic

design image
Posterior cerebral artery (P2 Segment)

The posterior cerebral artery (PCA) is divided into several segments, of which the P2 segment follows the P1–P2 junction at the posterior communicating artery. The P2 segment courses posteriorly around the midbrain within the ambient cistern, lying lateral to the cerebral peduncle. It gives rise to temporal branches (anterior, middle, and posterior temporal arteries) and parieto-occipital branches, supplying the inferomedial temporal lobe, hippocampus, parahippocampal gyrus, and occipital lobe.

The P2 segment is clinically significant because it is a common site of aneurysms and ischemic infarcts, and it forms important collateral pathways with MCA and ACA territories.

Synonyms

  • PCA P2 segment

  • Ambient segment of posterior cerebral artery

  • PCA ambient cistern segment

Function

  • Supplies blood to the inferior temporal lobe (including hippocampus and parahippocampal gyrus)

  • Perfuses the occipital lobe (visual cortex), contributing to visual processing

  • Provides branches to the thalamus and midbrain via perforators

  • Contributes to collateral circulation through anastomoses with MCA and ACA branches

MRI Appearance

T1-weighted images (non-contrast):

  • Vessel lumen appears as a flow void (signal loss) against surrounding brain tissue

  • Larger cortical branches are indirectly identified along cisternal and sulcal courses

T2-weighted images:

  • P2 segment also appears as a flow void due to fast flow

  • Hyperintense parenchymal changes in the occipital or temporal lobes suggest infarction in the P2 territory

MRA (Magnetic Resonance Angiography):

  • Time-of-flight (TOF) and contrast-enhanced MRA show the P2 segment curving around the midbrain

  • Normal P2 is seen as a bright enhancing tubular structure within the ambient cistern

  • MRA detects stenosis, occlusion, aneurysms, and vascular malformations

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Demonstrates intense vessel enhancement

  • Useful to delineate small P2 branches and evaluate for vasculitis, aneurysms, or tumor encasement

CT Appearance

Non-contrast CT:

  • Artery itself is not directly visualized, but hyperdense artery sign may indicate thrombosis in acute infarct

  • Infarcts in the P2 territory appear as hypodense areas in the occipital and temporal lobes

CT Angiography (CTA):

  • Clearly depicts the P2 segment wrapping around the midbrain in the ambient cistern

  • Lumen opacification allows evaluation for stenosis, occlusion, aneurysm, or AVM

  • CTA is particularly important for aneurysm detection at the P1–P2 junction and distal PCA mapping in stroke

MRI images

Posterior cerebral artery (P2 Segment)