CT angiography demonstrates variant anatomy of the anterior circulation with an accessory ACA that arises from and courses parallel to the right ACA.
In addition, there is aneurysmal dilatation at the origin of the accessory artery in the region of the right A1/proximal A2 measuring 2.5 mm in diameter, thought to be the culprit of the acute subarachnoid haemorrhage.
The left ACA is seen separately with no anterior communicating artery between the two systems.
No other focal aneurysmal disease.