What is the effectiveness of deploying a flow diverting stent over a previously placed regular intracranial stent for brain aneurysm treatment?

Flow Diverting Stent Deployment Over Previously Placed Intracranial Stent for Brain Aneurysm Treatment

Deploying a flow diverting stent over a previously placed regular intracranial stent should be avoided for saccular aneurysms that are amenable to either primary coiling or clipping due to higher risk of complications. 1

Evidence-Based Rationale

Current Guideline Recommendations

The 2023 American Heart Association/American Stroke Association (AHA/ASA) guidelines provide clear direction regarding flow diverters in aneurysm treatment:

• For patients with aneurysmal subarachnoid hemorrhage (aSAH) from ruptured saccular aneurysms amenable to either primary coiling or clipping, stents or flow diverters should not be used to avoid higher risk of complications (Class 3: Harm; Level B-NR) 1

• Flow diverters should be reserved for specific cases:

  • Ruptured wide-neck aneurysms not amenable to surgical clipping or primary coiling (Class 2a; Level C-LD) 1
  • Ruptured fusiform/blister aneurysms (Class 2a; Level C-LD) 1

Technical Considerations and Complications

When considering deploying a flow diverting stent over a previously placed regular stent, several important technical issues arise:

1. Increased thrombogenicity risk: The use of stent-assisted coiling and flow diverters has a higher risk of thrombogenicity than primary coiling, necessitating dual antiplatelet therapy 1

2. Hemorrhagic complications: In ruptured aneurysms, there is a higher risk of hemorrhagic complications, particularly ventriculostomy-related hemorrhage 1

3. Metal artifact challenges: Follow-up imaging is complicated by metal artifacts from multiple stents, making surveillance more difficult 1

4. Parent vessel stenosis: Significant parent artery stenosis at 6 months occurred in 33% of cases with flow diverters in one study 2

Efficacy of Flow Diverters

Despite the concerns, flow diverters can be effective in specific scenarios:

• Complete occlusion rates of 69% at 6 months have been reported with flow diverter stents alone 2
• The FRED flow-diverter study showed complete occlusion in 73% of aneurysms at 6-month follow-up 3
• Pipeline flow-diverting stent demonstrated 91.9% occlusion rate according to the last angiography in another study 4

Algorithmic Approach to Decision-Making

1. First, determine if the aneurysm is amenable to primary coiling or clipping:

   • If yes → avoid using flow diverters over existing stents
   • If no → proceed to step 2

2. Evaluate aneurysm morphology:

   • For wide-neck aneurysms not amenable to clipping/primary coiling → flow diverter reasonable
   • For fusiform/blister aneurysms → flow diverter reasonable
   • For saccular aneurysms amenable to other treatments → avoid flow diverters

3. Consider patient-specific factors:

   • Ability to tolerate dual antiplatelet therapy
   • Need for long-term imaging surveillance
   • Risk of parent vessel stenosis

Important Caveats and Pitfalls

• Dual antiplatelet therapy requirement: Patients must be able to tolerate and comply with long-term dual antiplatelet therapy
• Imaging follow-up challenges: Metal artifacts from multiple stents make surveillance more challenging
• Delayed complications: Despite the potential interest of flow-diverter stents to treat complex intracranial aneurysms, the delayed complication rate is quite high 2
• Mortality and morbidity: Studies report mortality rates of 2.2-4% and morbidity rates of 15% with flow diverters 2, 4

In conclusion, while technically feasible in certain scenarios, deploying a flow diverting stent over a previously placed regular intracranial stent should be approached with caution and reserved for cases where other treatment options are not viable, particularly for complex aneurysms not amenable to conventional treatments.