Cerebral Aneurysms, Saccular

Please see other articles for fusiform cerebral aneurysms


Saccular Intracranial aneurysms, Saccular Cerebral aneurysms, saccular aneurysms


Catheter angiography is the gold standard
MRA and CTA can also be used as good screening tests

Clinical features:

  • Asymptomatic
  • SAH signs and symptoms
  • Occulomotor nerve palsy
  • Trigeminal neuralgia
  • Visual field cut (optic nerve compression)
  • Cavernous sinus syndrome
  • Epistaxis (very rare, may occur in cavernous aneurysms)
  • Hydrocephalus signs and symptoms (typically with unruptured giant aneurysms or ruptured aneurysms)
  • Headache

Features on investigations:

Angiography, rotational angiography: gold standard

  • Round lobulated outpouching from an artery.
  • Assess for:
    • Location
    • Bifurcation vs. sidewall morphology
    • Neck: May have narrow or broad base (neck) i.e. <4mm or >4mm
    • Relationship to parent vessels and near by branches
    • Collateral circulation
    • Single lobe vs. multilobed
    • Aspect ratio: height of aneurysm/neck width. If >3, very high risk of rupture.


  • Good for intracranial aneurysms >5mm in diameter


  • Mycotic aneurysm are usually more peripheral i.e. in the smaller branches
  • Good for intracranial aneurysms >5mm


  • May show hyperdense aneurysm (mural calcium +/-thrombus)
  • Enhances in the patent area. Rim enhancement if thrombosed
  • Insufficient as a screening test on its own


  • T1: out pouching in artery, may show laminated thrombus
  • T2: flow void, hypointense
  • Rim enhancement if thrombosed
  • Insufficient as a screening test on its own


  • Thin-walled sac attached to a vessel
  • Microscopically: fibrocollagenous wall +/-thrombus. Loss of elastic fibres & smooth muscle at junction between sac & vessel (neck).


  • Giant >25 mm
  • Large 12-24 mm
  • Medium 5-11 mm
  • Small < 5 mm
  • Very small <3mm
  • Usual size 5-7mm

Classification/naming of Saccular aneurysms:

Common locations:

  • Anterior circulation more common than posterior circulation
  • Internal carotid ICA-posterior communicating artery PCOM junction “posteriorly directed”
  • Anterior cerebral artery ACA-Anterior communicating artery ACOM junction
  • M1-M2 division of MCA
  • Basilar artery BA-posterior cerebral artery PCA junction
  • Other locations:
    • PICA, especially PICA-VA junction, distal PICA aneurysms may occur (usually dissecting, not saccular)
    • ICA Paraclinoid aneurysms (cavernous, ophthalmic “directed upward a.k.a. carotid-ophthalmic”, superior hypophyseal “directed downward and medially towards the sella turcica” groups)
    • AChA aneurysms “posteriorly and laterally directed”
    • Petrous ICA (very rare, extra-dural)
Locations and names:
  • ICA aneurysm (terminus/bifurcation, PCOM aneurysms, AChA aneurysms , paraclinoid the following; cavernous, ophthalmic, superior hypophyseal), MCA aneurysm (M1 bifurcation), ACA aneurysm (A1-A2 junction, pericallosal-callosomarginal junction “less common”, A1 segment “rare”), ACOM aneurysm,
  • Basilar artery aneurysm (tip/bifurcation, BA-SCA junction, BA-AICA junction, BA-VA junction), Vertebral artery aneurysm (VA-PICA junction), PCA aneurysm (rare),
Giant aneurysms locations (>25 mm):
  • Anterior circulation (cavernous ICA aneurysm, supraclinoid ICA aneurysm, ACA aneurysm, MCA aneurysm)
  • Posterior circulation (BA aneurysm, PCA aneurysm)


  • Initially by catheter angiography, subsequently by MRA or CTA if small and stable over time


If ruptured:

If un-ruptured:

  • Options are:
    • Observation: catheter angiogram initially, subsequently by MRA or CTA if small and stable over time
    • Endovascular treatment options: coiling (unassisted), balloon-assisted coiling (balloon remodeling technique), stent-assisted coiling, flow diversion (flow diverting stent), parent vessel occlusion (vessel sacrifice)
    • Surgical treatment options: surgical clipping, bypass with vessel sacrifice.
  • Risk vs. benefit of treatment:
    • Decide if the aneurysm needs treatment based on size, location, life-expectancy and risk factors for rupture, technical ease vs. difficulty of treatment
    • If <10mm, low risk of rupture ~0.05% per year. But risk is determined on length of follow up, smoking status & other factors.
    • If =or>25mm (giant aneuryms), high risk of rupture ~6% in 1st year
  • Choice of therapy:
    • Basilar tip aneurysms: Endovascular rather than surgery.
    • Cavernous internal carotid artery: Endovascular rather than surgery
    • MCA territory: traditionally, surgery rather than Endovascular. Although this is changing as endovascular treatment has improved.
    • Neck <5mm & Neck:largest aneurysm diameter ratio (neck to dome ratio) <0.5: suggests good outcome with unassisted coiling. If these features are not present than balloon-assisted coiling, stent-assisted coiling or flow diverting stent or other techiques is necessary

Related articles:


  1. Unruptured intracranial aneurysms–risk of rupture and risks of surgical intervention. International Study of Unruptured Intracranial Aneurysms Investigators. N Engl J Med, 1998. 339(24): p. 1725-33.