What are the risks of placing a flow-diverting stent to treat Middle Cerebral Artery (MCA) bifurcation aneurysm?

Risks of Flow Diverting Stents for MCA Bifurcation Aneurysms

Flow diverting stents for MCA bifurcation aneurysms carry a high risk of thromboembolic complications (up to 16.7%) and should generally be avoided in favor of surgical clipping, which has better outcomes for this specific anatomical location. 1, 2

Major Risks of Flow Diverting Stents for MCA Bifurcation Aneurysms

Thromboembolic Complications

• Thromboembolic events occur in 16.7% of MCA bifurcation aneurysms treated with flow diversion 2
• Ischemic complications confirmed by MRI can occur in up to 43% of patients 3
• These complications are likely related to:
  • Impaired flow in jailed side branches at the bifurcation
  • Need for dual antiplatelet therapy (which increases hemorrhagic risk)
  • Complex deployment in bifurcation anatomy

Procedural Complications

• Procedure-related morbidity ranges from 8.6% to 21% 3, 4
• Risk of arterial rupture during balloon angioplasty when attempting to fully expand the stent 5
• Technical difficulties with stent deployment at bifurcation points
• Risk of stent fracture, particularly when manipulating previously stented regions 5

Efficacy Concerns

• Inferior occlusion rates compared to surgical clipping for MCA bifurcation aneurysms 2
• Complete occlusion rates vary widely (62-95%) depending on follow-up duration 3, 4
• Delayed occlusion is common, with many aneurysms requiring 12+ months for complete occlusion 4

Need for Dual Antiplatelet Therapy

• Higher risk of hemorrhagic complications, particularly ventriculostomy-related hemorrhage in ruptured aneurysms 1
• Contraindicated in acute subarachnoid hemorrhage when possible 1
• Compliance issues with long-term antiplatelet therapy

Anatomical Considerations Increasing Risk

Bifurcation Complexity

• MCA bifurcations are prone to lesion development due to greater shear stress and turbulent blood flow 1
• Bifurcation lesions are bulky and PCI is complicated by plaque shift in 4.5% to 26% of patients 1
• Risk of jailing important side branches at the MCA bifurcation

Treatment Strategy Considerations

• Single-stent techniques have lower TLR rates (<5%) compared to two-stent techniques (up to 25%) 1
• Y-stent configurations may be required for bifurcation aneurysms, increasing procedural complexity 6
• Restenosis is often confined to branch ostia (82% of cases) 1

Evidence-Based Recommendations

The 2023 American Heart Association/American Stroke Association guidelines note that:

• For MCA bifurcation aneurysms specifically, surgical clipping may be superior to endovascular treatment 1
• Within the cohort of patients >65 years in the ISAT trial, clipping was superior for MCA aneurysms 1
• Flow diverters should be avoided in the acute phase of ruptured aneurysms whenever possible 1

Risk Mitigation Strategies

• Careful patient selection is critical - avoid flow diversion for MCA bifurcation aneurysms when surgical clipping is feasible
• Consider alternative endovascular approaches such as conventional coiling or balloon-assisted techniques
• If flow diversion is absolutely necessary:
  • Use IVUS for accurate assessment and optimal stent placement
  • Consider single-stent technique when possible
  • Ensure proper dual antiplatelet therapy management
  • Plan for longer angiographic follow-up (12+ months)

Flow diversion for MCA bifurcation aneurysms remains controversial with higher complication rates than traditional approaches, and should be considered only when conventional treatment options are not feasible.