Can subarachnoid hemorrhage (SAH) due to a blister aneurysm at the A1- Anterior Cerebral Artery (ACA) location be treated with endovascular flow diversion?

Treatment of Blister Aneurysms at A1-ACA with Flow Diversion

Yes, endovascular flow diversion is a reasonable treatment option for ruptured blister aneurysms at the A1-ACA location to reduce mortality, though this represents a challenging clinical scenario with important caveats. 1

Guideline-Based Recommendation

The 2023 AHA/ASA guidelines specifically state that for patients with aSAH from ruptured fusiform/blister aneurysms, the use of flow diverters is reasonable to reduce mortality (Class 2a, Level C-LD). 1 This recommendation distinguishes blister aneurysms from typical saccular aneurysms, where flow diversion is explicitly contraindicated due to higher complication rates. 1

Critical Distinction from Saccular Aneurysms

• Flow diverters should NOT be used for ruptured saccular aneurysms amenable to primary coiling or clipping due to increased complications (Class 3: Harm recommendation). 1
• Blister aneurysms receive different treatment guidance because they are not amenable to conventional surgical clipping or primary coiling due to their fragile wall structure and broad-based morphology. 1

Clinical Evidence Supporting Flow Diversion

Efficacy Data

• Immediate occlusion rates are high: Pipeline Embolic Device achieved immediate occlusion or near-occlusion in 9 of 10 patients with ruptured blister aneurysms, with complete occlusion on long-term follow-up (mean 15 months) in all survivors. 2
• Favorable outcomes: In the dual-center series, 8 of 9 surviving patients achieved 90-day mRS of 0, with one patient achieving mRS of 1. 2
• No procedure-related complications were observed in one series of 6 endovascularly treated patients, with no recurrent hemorrhage. 3

Location-Specific Considerations for A1 Segment

• A1 blister aneurysms are particularly challenging due to their location and the fragile nature of the vessel wall. 4
• Flow diversion has been successfully used even for anterior communicating artery complex blister aneurysms by deploying flow diverters in both A1/A2 junctions to exclude the aneurysm. 5
• Parent vessel occlusion (surgical clipping or endovascular trapping) remains an alternative if the patient tolerates vessel sacrifice, though this is more commonly considered for ICA blister aneurysms. 4, 6

Treatment Algorithm for A1 Blister Aneurysms

Step 1: Confirm Diagnosis

• High suspicion in setting of diffuse SAH with small, broad-based lesion on dorsal/medial wall of A1 segment. 4
• Angiographic appearance may show wall irregularity rather than discrete aneurysm sac. 5

Step 2: Assess Treatment Options

• Flow diversion is preferred if technically feasible, given guideline support for blister aneurysms. 1
• Surgical options (direct clipping, wrapping, or parent vessel sacrifice) have historically shown high rates of regrowth and rebleeding. 2, 4
• Conventional endovascular coiling (with or without stent/balloon assistance) shows high regrowth rates and should be avoided. 6

Step 3: Antiplatelet Management

• Dual antiplatelet therapy is required for flow diversion, which increases hemorrhagic risk in acute SAH setting. 3
• Load with aspirin and P2Y12 inhibitor prior to or immediately after device deployment. 3
• This represents the primary risk of flow diversion in the acute hemorrhage setting. 1

Step 4: Follow-up Protocol

• First angiographic follow-up at 6-7 months to assess complete occlusion. 2, 3
• Monitor for mild, transient intimal hyperplasia (observed in 2 of 6 patients in one series, clinically asymptomatic). 3
• Long-term surveillance necessary given historical concerns about durability. 2

Important Caveats and Pitfalls

Antiplatelet Therapy Risk

• The requirement for dual antiplatelet therapy in the acute SAH period represents a significant hemorrhagic risk that must be weighed against rebleeding risk from untreated aneurysm. 3
• This is the primary reason flow diverters carry a Class 3: Harm recommendation for typical saccular aneurysms. 1

Alternative Considerations

• Parent vessel occlusion may be safer if collateral circulation is adequate, avoiding need for antiplatelet therapy. 4, 6
• For A1 location specifically, assess contralateral A1 dominance and anterior communicating artery patency before considering vessel sacrifice. 5, 4

Timing

• Early treatment is essential (within 24-72 hours) to reduce rebleeding risk, which is particularly high with blister aneurysms. 1
• Flow diversion can be performed emergently in the acute SAH phase. 3, 5