What is the recommended treatment approach for patients with blister aneurysm subarachnoid hemorrhage in the A1-anterior cerebral artery segment, considering endovascular flow diversion as an option?

Endovascular Flow Diversion for Blister Aneurysms in the A1-ACA Segment

For ruptured blister aneurysms in the A1-anterior cerebral artery segment presenting with subarachnoid hemorrhage, endovascular flow diversion is a reasonable treatment option when conventional clipping or coiling is not feasible, with case series demonstrating successful aneurysm occlusion and acceptable outcomes despite the inherent challenges of antiplatelet therapy in the acute hemorrhagic setting. 1

Guideline Support for Flow Diversion in Blister Aneurysms

The 2023 AHA/ASA guidelines provide Class 2a, Level C-LD recommendation specifically stating that for patients with aSAH from ruptured fusiform/blister aneurysms, the use of flow diverters is reasonable to reduce mortality. 1 This represents an evolution from earlier guidelines that were more cautious about flow diversion in the acute SAH setting. 1

The guidelines emphasize that blister aneurysms represent a distinct category where flow diversion may be preferred over traditional approaches because:

• Complete obliteration with conventional clipping or coiling is often not feasible due to the fragile aneurysm wall 1
• The risk of not treating is very high given the propensity for early rebleeding 1

Case Series Evidence for A1 Segment Blister Aneurysms

Acute Phase Treatment Outcomes

A 2018 case series of eight consecutive ruptured blister aneurysms treated with flow diversion in the acute SAH phase demonstrated:

• 100% technical feasibility with no procedure-related complications 2
• Zero recurrent hemorrhages despite antiplatelet therapy requirements 2
• Complete aneurysm occlusion in all cases at first angiographic follow-up 2
• Two patients developed mild, transient intimal hyperplasia without clinical symptoms or need for treatment 2

Specific A1 Segment Case Reports

Mid-A1 blister aneurysm: A case report described successful treatment of a mid-A1 blister aneurysm presenting with diffuse basal SAH, though this case was managed with surgical parent vessel clipping rather than flow diversion. 3 This highlights that A1 location presents unique anatomical challenges.

AComA/A1-A2 junction approach: A 2013 case described endovascular exclusion of the anterior communicating artery by deploying two flow-diverting stents in both A1/A2 junctions for a ruptured blister aneurysm. 4 The patient had:

• Uneventful hospital course 4
• Complete aneurysm exclusion at 3-month follow-up 4
• Complete AComA exclusion with patent bilateral ACAs 4
• No persistent arterial wall irregularities 4

Antiplatelet Management Strategy

The critical challenge with flow diversion in acute SAH is balancing thromboembolism prevention against rebleeding risk. A 2023 series demonstrated a viable single-antiplatelet protocol: 5

Periprocedural regimen:

• Weight-adapted eptifibatide IV plus heparin IV during procedure 5
• Switch to oral prasugrel monotherapy after 6-24 hours 5

Outcomes with this protocol (n=9 ruptured aneurysms):

• Eight patients treated within 24 hours of symptom onset 5
• One fatal re-rupture (11% mortality) 5
• Zero thromboembolic events in survivors 5
• Complete occlusion in 6/8 survivors, subtotal occlusion in 2/8 5
• Favorable clinical outcome in 5/8 survivors (63%) 5

This represents a significant advancement over traditional dual-antiplatelet therapy concerns that previously limited flow diversion use in acute SAH. 1

Treatment Algorithm for A1 Blister Aneurysms

Step 1: Multidisciplinary evaluation

• Immediate assessment by both neurosurgical and endovascular specialists 1
• Determine if conventional clipping or coiling is technically feasible 1

Step 2: If conventional treatment not feasible:

• Consider flow diversion as primary option for blister morphology 1
• Assess parent vessel anatomy and collateral circulation 4

Step 3: Endovascular approach options:

• Single flow-diverting stent across aneurysm if parent vessel can be preserved 2, 6
• Bilateral A1/A2 flow diverters with AComA exclusion if aneurysm involves AComA complex 4
• Parent vessel occlusion if collateral flow adequate and reconstruction not possible 2

Step 4: Antiplatelet protocol:

• Periprocedural eptifibatide IV + heparin IV 5
• Transition to prasugrel monotherapy within 6-24 hours 5
• Avoid dual-antiplatelet therapy if using phosphoryl-bonded flow-diverting stents 5

Step 5: Blood pressure management:

• Maintain systolic BP <160 mmHg before aneurysm treatment 1, 7
• Maintain mean arterial pressure >90 mmHg after securing 7

Critical Pitfalls to Avoid

Do not delay treatment: Blister aneurysms have extremely high early rebleeding rates, and treatment should be performed as an emergency. 4, 2 The 2023 guidelines recommend aneurysm obliteration within 24 hours of aSAH. 1

Do not assume angiographic-negative SAH excludes blister aneurysm: Maintain high suspicion in asymmetrically diffuse SAH patterns, as blister aneurysms may be subtle or initially missed. 3 Repeat angiography may be necessary. 1

Do not use standard dual-antiplatelet protocols reflexively: Newer phosphoryl-bonded flow-diverting stents with reduced thrombogenicity allow single-antiplatelet regimens that significantly reduce rebleeding risk. 5

Do not attempt conventional coiling alone: The fragile wall and small sac of blister aneurysms make primary coiling technically challenging and associated with high failure rates. 1, 2

Angiographic Follow-up Requirements

All patients treated with flow diversion require delayed follow-up vascular imaging, with timing individualized based on initial occlusion status. 1 In the reported series:

• First follow-up typically at 3 months demonstrated complete or near-complete occlusion 2, 5
• One-year follow-up confirmed durability 5
• Monitor for intimal hyperplasia, which may occur but is typically transient and asymptomatic 2