Saccular or berry aneurysms are round, berry-like outpouchings that arise from arterial bifurcation points. Recent studies have shown that most intracranial aneurysms probably result from haemodynamically induced degenerative vascular injury, not a congenital, developmental, or inherited weakness of the arterial wall. The true incidence of intracranial aneurysm is unknown. The incidence of incidentally demonstrated intracranial aneurysms varies between 1% and 5%. They are multiple in 15-20% of all cases and typically become symptomatic between the ages of 40 and 60 years. The most common symptom is subarachnoid haemorrhage, as seen in this patient.
Most intracranial aneurysms (approximately 90%) arise in the carotid circulation. 30-35% of aneurysms arise from the anterior communicating artery, 30-35% from the posterior communicating artery origin, 20% from the middle cerebral artery bifurcation, 5% from the basilar artery bifurcation or tip and the remaining 1-5% arise from other posterior fossa vessels. Saccular aneurysms larger than 2.5cm are called giant aneurysms.
Although MR angiography appears promising, catheter angiography is usually required for the definitive diagnosis and preoperative delineation of intracranial aneurysms.