Find the aneurysm on CT or MR angiography, then describe what the neuro-interventionalist needs: location, size, neck width, dome-to-neck ratio, branches from the neck, irregularity (blebs) — the features that decide coiling, clipping or surveillance.
Orient first
- Most arise at the circle of Willis bifurcations: anterior communicating, posterior communicating, MCA bifurcation, basilar tip.
- In subarachnoid haemorrhage the blood distribution points to the likely site; multiple aneurysms are common.
- Rupture risk scores (e.g. PHASES — verify) use size, location, age, hypertension and previous SAH.
Acquire the study
- CT angiography from the arch to the vertex, 0.6–1 mm, with MIP and volume rendering.
The manoeuvre
- Review each circle of Willis segment on thin axial source images and 3D; search the pericallosal and distal MCA branches.
- Measure dome height, width and neck in mm; dome-to-neck ratio.
- Branches arising from the neck; blebs and lobulation.
- In SAH: the aneurysm nearest the thickest clot is the likely bleeder.
What confirms it
- A saccular outpouching demonstrated on angiography in two projections.
What licenses you to exclude it
- A negative CTA in SAH does not exclude a small aneurysm — catheter angiography is the next step.
The classic misread
- Missing a small aneurysm at the skull base in bone — use bone subtraction or thin MIPs.