Review: Blood Flow Diversion is an Option for Some Ruptured Brain Aneurysms
Key findings
- Concerns about using flow diversion for ruptured aneurysms center on the risk of hemorrhage from the aneurysm after treatment, and the risk of complications from antiplatelet agents
- There is evidence that flow diversion might be more effective than conventional treatment for ruptured blister aneurysms and large or giant saccular aneurysms
- The literature is still unclear about the safety of dual antiplatelet therapy for patients with ruptured aneurysms, especially those who present with subarachnoid hemorrhage
- All these issues are being explored in prospective randomized, controlled studies
Blood flow diversion is emerging as a treatment option for many types of brain aneurysms that are not well suited to conventional modalities. To date, though, its use has been reserved principally for unruptured aneurysms.
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In Neurocritical Care, Aman Patel, MD, director of Cerebrovascular and Endovascular Neurosurgery at Massachusetts General Hospital, and colleagues describe why flow diversion is a good alternative to clipping or coiling for many ruptured aneurysms. They based their comments on a review of medical literature published between January 2000 and June 2016.
Overview
A flow-diverting stent works by redirecting blood flow away from an aneurysm. Immediately after the stent is placed, blood flow stagnates within the aneurysm dome and undergoes thrombosis. Over time, a new endothelium develops across the neck, thus reconstructing the parent vessel and curing the aneurysm.
Dr. Patel and his colleagues explain that two concerns have kept neurosurgeons from using flow diversion for ruptured aneurysms:
- Risk of hemorrhage from an aneurysm after treatment. Flow diversion does not usually eliminate blood flow immediately, which leaves an aneurysm vulnerable to re-rupture in the acute period. How long it takes for an aneurysm to become occluded has not been well studied
- Risk of complications from antiplatelet use. To prevent thromboembolism associated with the stent, dual antiplatelet therapy is required. Some experts believe this requirement shifts the risk:benefit ratio away from flow diversion because of the potential for hemorrhagic complications with antiplatelet agents.
Still, flow diversion might be more effective than conventional treatment for certain types of aneurysms, the authors say. They focus on blister aneurysms and large or giant saccular aneurysms.
Ruptured Blister Aneurysms
Blister aneurysms, also called dissecting aneurysms or pseudoaneurysms, are so difficult to treat with clipping or coiling that some surgeons have tried flow diversion as a primary treatment method.
For the most part, this approach has been described only in case reports, case series and single-center retrospective case series, Dr. Patel's group found. No randomized, controlled study of any treatment for blister aneurysms has been published.
The highest-level evidence that the authors found, in terms of studies limited to endovascular procedures for blister aneurysms, was a meta-analysis of 265 patients. Of these, 62 received flow-diverting stents, with a 90.8% rate of mid- to long-term complete occlusion and a low rate of retreatment (6.6%).
Ruptured Large and Giant Saccular Aneurysms
Large and giant (≥15 mm) saccular aneurysms commonly present with subarachnoid hemorrhage. The use of flow diversion in such cases has been limited by concern over the delayed treatment effect. In addition, rare early bleeding from an aneurysm has been reported, even in the treatment of unruptured aneurysms.
An adjunctive technique called coil packing of the aneurysm dome eliminates blood flow into the dome and provides protection from re-hemorrhage nearly immediately.
Some surgeons partially coil the ruptured aneurysm, then place the stent during a separate later procedure. The intention of that alternative strategy is to avoid the risk of hemorrhagic complications from antiplatelet therapy during the initial hospitalization for subarachnoid hemorrhage.
Antiplatelet Agents
Hemorrhagic complications are a major source of morbidity and mortality associated with the flow-diverting stent itself. The evidence is still mixed, Dr. Patel's group found, about whether significant bleeding complications occur when antiplatelet agents are administered to patients with ruptured aneurysms.
The other major source of morbidity and mortality with intracranial stents is thromboembolic complications. That risk is reportedly higher when patients present with subarachnoid hemorrhage.
In those cases, pretreating for a week or more with antiplatelet agents is impossible, the authors note, and there is controversy about how to proceed. They suggest giving aspirin and prasugrel just prior to surgery because unlike clopidogrel, prasugrel is effective in most individuals.
Prospective Trials Are Underway
Ongoing randomized, controlled trials should yield more guidance about treating ruptured aneurysms with flow diversion, the authors say. One is DIVERT, which will compare flow diversion with best standard therapy for ruptured blister aneurysms. Another is FIAT, which will evaluate the safety and effectiveness of flow diversion for ruptured large and giant aneurysms.