What is the difference between flow diverters (FD) and stents in the treatment of aneurysms?

Differences Between Flow Diverters and Stents in Aneurysm Treatment

Flow diverters (FDs) are specialized endovascular devices that reconstruct the parent artery to reduce blood flow into the aneurysm sac, causing stagnation and gradual thrombosis, while conventional stents primarily provide structural support for coil embolization. 1

Basic Differences

• Mechanism of Action:

  • Flow Diverters: Work by altering hemodynamics at the aneurysm/parent vessel interface to promote gradual thrombosis and inflammatory response leading to aneurysm shrinkage and vessel wall reconstruction 1
  • Conventional Stents: Primarily serve as a scaffold to prevent coil herniation into the parent vessel during coil embolization (stent-assisted coiling) 2

• Mesh Density:

  • Flow Diverters: Feature significantly higher mesh density (30-35% metal coverage) designed specifically to divert blood flow away from the aneurysm 3
  • Conventional Stents: Have lower mesh density primarily designed to support coils while maintaining branch vessel patency 2

• Treatment Goal:

  • Flow Diverters: Aim for complete vessel wall reconstruction and aneurysm exclusion over time 4
  • Conventional Stents: Typically used as adjuncts to coiling to achieve immediate aneurysm occlusion 2

Clinical Applications

• Aneurysm Types Suitable for Flow Diverters:

  • Large and giant unruptured aneurysms 5
  • Fusiform and dissecting aneurysms 4
  • Wide-necked aneurysms with low dome-to-neck ratio 4
  • Complex internal carotid artery aneurysms 6

• Aneurysm Types Suitable for Stent-Assisted Coiling:

  • Wide-necked saccular aneurysms that are not amenable to primary coiling 2
  • Smaller aneurysms requiring immediate occlusion 2

Efficacy Comparison

• Occlusion Rates:

  • Flow Diverters: Achieve significantly higher complete occlusion rates (81.5%) at 6-month follow-up compared to conventional stents 5, 4
  • Stent-Assisted Coiling: Generally shows lower complete occlusion rates and higher recurrence rates compared to flow diverters 5

• Progressive Occlusion:

  • Flow Diverters: Demonstrate continued improvement in occlusion rates over time as vessel remodeling occurs 4
  • Stent-Assisted Coiling: Typically achieve maximum occlusion immediately after the procedure with potential for compaction and recurrence 5

Safety Considerations

• Antiplatelet Requirements:

  • Both Devices: Require dual antiplatelet therapy, but this is particularly critical with flow diverters due to higher thrombogenicity 2
  • Ruptured Aneurysms: Use of stents or flow diverters in ruptured aneurysms is associated with higher risk of hemorrhagic complications, particularly with ventriculostomy 2

• Complication Rates:

  • Flow Diverters: Associated with non-negligible rates of ischemic (4.1%) and hemorrhagic (2.9%) complications 4
  • Neurological Morbidity: Flow diverters have approximately 3.5% morbidity and 3.4% mortality rates 4

Specific Clinical Scenarios

• Ruptured Aneurysms:

  • Guidelines Recommendation: "The use of stents or flow diverters should be avoided in the acute phase whenever a ruptured aneurysm can be treated by primary coiling or clipping" 2

• Age Considerations:

  • Younger Patients (<40 years): Clipping might be preferred due to better long-term protection from rerupture 2
  • Older Patients (>70 years): No clear benefit of coiling over clipping has been demonstrated 2

• Aneurysm Location:

  • Posterior Circulation: Coiling is indicated in preference to clipping for ruptured aneurysms 2
  • Middle Cerebral Artery: Clipping may be superior for ruptured MCA aneurysms 2

Important Clinical Pitfalls

• Delayed Complications with Flow Diverters:

  • Risk of delayed aneurysm rupture after flow diversion 6
  • Perianeurysmal edema and distant hemorrhages can occur 1
  • Potential for side branch or perforator occlusion despite theoretical preservation 1

• Antiplatelet Management:

  • Inadequate antiplatelet therapy with flow diverters significantly increases thromboembolic risk 1
  • Dual antiplatelet therapy creates challenges in managing potential neurosurgical interventions like ventriculostomy 2

• Patient Selection:

  • Proper patient selection is critical to avoid complications with flow diverters 4
  • Flow diverters should not be used for ruptured saccular aneurysms amenable to either primary coiling or clipping 2

Current Guidelines Recommendations

• For patients with ruptured wide-neck aneurysms not amenable to surgical clipping or primary coiling, endovascular treatment with stent-assisted coiling or flow diverters is reasonable to reduce rebleed risk 2

• For patients with ruptured fusiform/blister aneurysms, flow diverters are reasonable to reduce mortality 2

• For patients with ruptured saccular aneurysms amenable to either primary coiling or clipping, stents or flow diverters should not be used due to higher complication risk 2