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Posterior cerebral artery (P3 Segment)

The P3 segment of the posterior cerebral artery (PCA), also called the quadrigeminal segment, extends from the posterior margin of the midbrain (quadrigeminal cistern) to the anterior limit of the calcarine fissure. It lies within the quadrigeminal cistern, coursing around the midbrain, and gives rise to important cortical branches, including the parieto-occipital artery and calcarine artery, which supply the occipital lobe and visual cortex.

The P3 segment plays a critical role in visual processing and is a common site of involvement in posterior circulation strokes, which may result in contralateral homonymous hemianopia.

Synonyms

  • Quadrigeminal segment of PCA

  • P3 segment of posterior cerebral artery

  • Cortical branch–originating PCA segment

Function

  • Supplies blood to the occipital lobe, especially the primary visual cortex

  • Provides circulation to the posterior parietal cortex and parts of the inferior temporal lobe

  • Maintains collateral circulation through anastomoses with middle cerebral artery (MCA) branches

  • Critical for visual function and higher-order visual integration

MRI Appearance

T1-weighted images (non-contrast):

  • Appears as a flow void (signal loss) along the quadrigeminal cistern

  • Vessel lumen not directly visualized without angiography

T2-weighted images:

  • PCA P3 demonstrates flow voids, surrounded by hyperintense CSF in the quadrigeminal cistern

  • Adjacent parenchymal hyperintensity may suggest ischemia or infarction in the occipital lobe

MRA (Magnetic Resonance Angiography):

  • Time-of-flight (TOF) and contrast-enhanced MRA clearly show the P3 course in the quadrigeminal cistern and its branching pattern

  • Normal artery demonstrates a bright enhancing lumen

  • MRA is excellent for evaluating stenosis, occlusion, aneurysm, or vascular malformations

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Vessel lumen enhances strongly

  • Particularly helpful in identifying abnormal vascular patterns, small cortical branches, or collateral pathways

CT Appearance

Non-contrast CT:

  • P3 itself is not directly seen unless thrombosed, where a hyperdense artery sign may be present

  • Infarctions in its vascular territory appear as hypodense changes in the occipital lobe

CT Angiography (CTA):

  • Clearly visualizes the origin, course through the quadrigeminal cistern, and branching arteries

  • Demonstrates stenosis, occlusion, aneurysm, or AVM

  • CTA is the modality of choice for stroke assessment and surgical planning of PCA pathology