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Precommunicating part of posterior cerebral artery

The precommunicating part of the posterior cerebral artery, commonly referred to as the P1 segment, is the proximal portion of the posterior cerebral artery extending from the terminal bifurcation of the basilar artery to the junction with the posterior communicating artery. It forms a key component of the posterior circulation and the Circle of Willis, supplying critical deep and posterior brain structures.

The P1 segment is an important anatomical and radiological landmark, particularly in vascular imaging, stroke localization, and assessment of collateral circulation.

Synonyms

  • P1 segment of the posterior cerebral artery

  • Precommunicating PCA

Location

  • Begins at the terminal bifurcation of the basilar artery

  • Ends at the origin of the posterior communicating artery

  • Courses posterolaterally around the midbrain

  • Located within the interpeduncular cistern

  • Forms the proximal portion of the posterior cerebral artery

  • Constitutes the posterior part of the Circle of Willis

Anatomical course

  • Arises from the basilar artery apex

  • Runs laterally and posteriorly

  • Encircles the cerebral peduncle

  • Transitions into the P2 segment after the posterior communicating artery

  • Maintains close relationship with midbrain perforators

Relations

Anteriorly:

  • Interpeduncular cistern

  • Oculomotor nerve (CN III)

Posteriorly:

  • Midbrain (cerebral peduncle)

Superiorly:

  • Thalamus (via perforating branches)

Inferiorly:

  • Pons and basilar artery apex

Medially:

  • Basilar artery

Laterally:

  • Posterior communicating artery origin

Branches

  • Thalamoperforating arteries:

    • Penetrate the posterior perforated substance

    • Supply thalamus and rostral midbrain

  • Short circumferential branches:

    • Supply midbrain structures

  • Contribution to posterior circulation:

    • Supports deep gray nuclei and brainstem perfusion

Structures supplied

  • Thalamus (paramedian regions)

  • Midbrain (rostral and medial portions)

  • Subthalamic region

  • Posterior limb of internal capsule (via perforators)

Function

  • Deep cerebral perfusion: Supplies vital diencephalic and mesencephalic structures

  • Brainstem support: Maintains blood flow to midbrain nuclei and tracts

  • Collateral circulation: Plays a role in posterior–anterior circulation balance via the Circle of Willis

MRI appearance (normal)

T1-weighted images:

  • P1 segment: Appears as a flow void within the interpeduncular cistern

  • Course: Smooth, linear or gently curving vascular structure

T2-weighted images:

  • Normal artery: Flow void with low signal intensity

  • Surrounding CSF: High signal, enhancing vessel conspicuity

FLAIR:

  • Normal: Vessel usually suppressed or minimally visible due to flowing blood

  • Anatomical identification: Best inferred by location rather than signal

Post-contrast T1-weighted images:

  • Normal: Linear enhancement corresponding to vascular lumen

CT appearance (normal)

Non-contrast CT:

  • P1 segment: Usually not directly visualized

Post-contrast CT / CT angiography:

  • P1 segment: Clearly visualized as a contrast-opacified vessel

MRI images

MRI Precommunicating part of posterior cerebral artery anatomy image -img-00000-00000

MRI images

MRIPrecommunicating part of posterior cerebral artery anatomy image -img-00000-00000