Background: Both a persistent primitive trigeminal artery (PTA) and the absence of an internal carotid artery are rare developmental anomalies.
Methods and results: Two cases with the unusual association of a persistent PTA and absence of the internal carotid artery on the left side are reported. The left anterior cerebral artery territory was supplied from the right internal carotid artery via the anterior communicating artery, and the left middle cerebral artery territory was supplied from the vertebrobasilar system via the persistent PTA antidromically.
Conclusion: This is the first report of such an association of developmental anomalies of cerebral vessels. Our cases are instructive for gaining insight into the involution and evolution processes of primitive cerebral arteries in the human embryo.