Saccular Aneurysm

KEY FACTS

Terminology

• Intracranial saccular aneurysm (SA)

• Outpouching affecting only part of arterial circumference

  • Lacks internal elastic lamina ± tunica media

Imaging

• Round/lobulated arterial outpouching

  • Usually arises from bifurcations of circle of Willis (COW), supraclinoid internal carotid and middle cerebral arteries

  • 90% occur in anterior circulation

  • 10% posterior circulation: Basilar tip, cerebellar arteries (posterior inferior cerebellar artery most common)

  • Rare (< 1%): Trigeminal artery, vertebrobasilar junction fenestration

• Ruptured SAs result in subarachnoid hemorrhage (SAH)

• May have mural Ca++

• Screening in suspected aneurysmal SAH

  • Multislice CTA sensitivity > 95% for SA > 2 mm

  • 3D TOF: > 90% sensitive for aneurysms ≥ 3 mm

  • DSA still considered “gold standard” but usually performed only if CTA negative or endovascular treatment contemplated

Top Differential Diagnoses

• Vessel loop

• Vessel infundibulum

• Fusiform aneurysm

• Flow void MR mimic (e.g., aerated anterior clinoid)

Clinical Issues

• Vast majority of unruptured SAs are asymptomatic

  • 2-6% incidental finding at autopsy, imaging

• 80-90% of nontraumatic SAH caused by ruptured SA

• Treatment

  • Endovascular coiling vs. surgical clipping still controversial

  • 22.6% relative, 6.9% absolute risk ↓ for coiling vs. surgery for ruptured aneurysms

  • ↓ morbidity, mortality, and hospital costs; quicker recovery for unruptured aneurysms

TERMINOLOGY

IMAGING