Vessel
Posterior communicating artery
An ICA–PCA connection that also supplies perforators
High-yield
An ICA–PCom aneurysm can compress CN III and cause diplopia, ptosis and pupillary enlargement. Pupil involvement is an important clue, but pupil sparing does not rule out an aneurysm.
Overview
PCom runs posteriorly from the supraclinoid ICA to the PCA near its P1–P2 junction. Its caliber ranges from very small to a dominant supply channel for a fetal-type PCA. Branches reach the hypothalamic, thalamic and subthalamic region. Its close relationship with the cisternal oculomotor nerve is clinically important.
Reference facts
- Origin
- Usually the posterior surface of the ICA's communicating segment, before its terminal bifurcation.
- Course
- Courses backward toward the PCA, usually above and medial to CN III; precise relationships change with arterial configuration.
- Branches
- Small perforators, including premammillary/tuberothalamic branches; number, origin and caliber vary.
- Supplies
- Parts of hypothalamus, thalamus, subthalamic region and neighboring capsular/optic pathways, plus a potential collateral or dominant route into PCA territory.
Clinical correlation
Compression and microvascular injury can both cause a third-nerve palsy. Pain and pupillary findings overlap, so they cannot reliably distinguish the causes by themselves. The arterial relationship explains why a new palsy requires clinical assessment rather than reliance on a simple pupil rule.
Frequently asked questions
Where does the posterior communicating artery originate?
Usually the posterior surface of the ICA's communicating segment, before its terminal bifurcation.
What does the posterior communicating artery supply?
Parts of hypothalamus, thalamus, subthalamic region and neighboring capsular/optic pathways, plus a potential collateral or dominant route into PCA territory.
What are the branches of the posterior communicating artery?
Small perforators, including premammillary/tuberothalamic branches; number, origin and caliber vary.
What is the course of the posterior communicating artery?
Courses backward toward the PCA, usually above and medial to CN III; precise relationships change with arterial configuration.