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Posterior Communicating Artery

arteria communicans posterior

The posterior communicating artery (PComA) arises from the internal carotid artery just before it bifurcates into the anterior and middle cerebral arteries. It runs posteriorly and medially to join the posterior cerebral artery, forming the lateral part of the circle of Willis. It is variable in size and may be hypoplastic or absent on one side, and occasionally a fetal-type PComA is the dominant supply to the posterior cerebral circulation.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The posterior communicating artery is the most common site of intracranial saccular aneurysm after the anterior communicating artery. A PComA aneurysm expanding at the junction with the ICA compresses the adjacent oculomotor nerve (CN III) as it passes between the PComA and the posterior cerebral artery, producing a painful, complete third nerve palsy with ptosis, mydriasis, and ophthalmoplegia. This combination is a neurosurgical emergency requiring urgent CT angiography and intervention.

Pathology

Common Injuries & Conditions

PComA Aneurysm

A saccular aneurysm at the ICA-PComA junction produces a painful complete third nerve palsy with a dilated unreactive pupil, ptosis, and ophthalmoplegia from direct oculomotor nerve compression, requiring urgent CT angiography followed by surgical clipping or endovascular coiling to prevent subarachnoid haemorrhage.

PComA Subarachnoid Haemorrhage

Rupture of a PComA aneurysm produces sudden-onset severe headache (thunderclap), meningism, and altered consciousness, with blood in the basal cisterns on CT, requiring critical care, vasospasm prevention, and aneurysm treatment within 24 hours.