Cerebral Aneurysms, Saccular

Diseases,

Please see other articles for fusiform cerebral aneurysms

Synonyms:

Saccular Intracranial aneurysms, Saccular Cerebral aneurysms, saccular aneurysms

Diagnosis:

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.

CTA:

  • Good for intracranial aneurysms >5mm in diameter

MRA:

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

CT:

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

MRI:

  • 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

Pathology:

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

Grading:

  • 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)

Monitor:

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

Treatment:

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:

References:

  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.