How do you determine the P2A (Posterior Cerebral Artery segment) and P2P (Posterior Cerebral Artery segment) junction of the posterior cerebral artery?

From the Guidelines

To determine the P2A and P2P junction of the posterior cerebral artery, you should identify where the PCA divides into its anterior and posterior segments at the point where the artery passes around the lateral aspect of the midbrain, typically occurring at the posterior edge of the cerebral peduncle. This junction is crucial in neurosurgery and neurointerventional procedures, and its accurate identification is essential for evaluating vascular pathologies affecting the posterior circulation [no direct evidence provided in 1]. When using angiography or other vascular imaging, the P2A segment supplies the inferior temporal lobe and continues until approximately the posterior ambient cistern, where it then becomes the P2P segment that supplies the occipital lobe. Some key anatomical landmarks to consider include:

• The lateral geniculate body, where the P2A runs from the posterior communicating artery to this point, and the P2P extends from this point to the calcarine fissure.
• The posterior edge of the cerebral peduncle, where the PCA transitions from running parallel to the midbrain to coursing laterally toward the temporal and occipital lobes. Although the provided study 1 discusses the use of catheter-directed angiography in the setting of highly suspected large vessel occlusion (LVO) with no need for perfusion imaging or MRI to determine eligibility for endovascular treatment (EVT), it does not directly address the determination of the P2A and P2P junction of the posterior cerebral artery. However, in real-life clinical practice, identifying this junction is critical for neurosurgeons and neurointerventionalists when planning procedures or evaluating vascular pathologies affecting the posterior circulation.

From the Research

Determining the P2A and P2P Junction of the Posterior Cerebral Artery

To determine the P2A (Posterior Cerebral Artery segment) and P2P (Posterior Cerebral Artery segment) junction of the posterior cerebral artery, several studies provide relevant information:

• The P2 segment of the posterior cerebral artery is divided into an anterior (P2A) and posterior (P2P) segment, with the P2A segment beginning at the posterior communicating artery and ending at the most lateral aspect of the cerebral peduncle, and the P2P segment extending from the most lateral aspect of the cerebral peduncle to the posterior edge of the lateral surface of the midbrain 2.
• The average length of the P2A segment is 23.6 mm, and the average length of the P2P segment is 16.4 mm 2.
• The P2 segment can be exposed surgically using different approaches, including the pterional approach, subtemporal approach, and occipital interhemispheric transtentorial approach, each providing a different view of the P2 segment 3.
• Computed tomography angiography (CTA) can be used to determine the blood supply dominance of the posterior cerebral artery, but its accuracy is limited, with a sensitivity and specificity of 69% and 96%, respectively, in predicting the presence of a fetal PCA 4.
• The distribution of aneurysms along the PCA segments, including the P2 segment, can be analyzed using angiographic studies, which can provide information on the location and size of aneurysms 5.
• Variations of the posterior cerebral artery, such as fenestration, early bifurcation, and duplication, can be diagnosed using MR angiography, and can affect the determination of the P2A and P2P junction 6.