Delayed Aneurysmal Rupture following Flow Diverter Placement despite Adjunctive Coiling: Case Report

Abstract

Introduction

Flow diverters significantly alter the inflow dynamics of an aneurysm, leading to both qualitative and quantitative changes in the intra-aneurysmal hemodynamic environment (AJNR Am J Neuroradiol. 2014 Aug 1;35(8):1567–73).

Case Presentation

A 65-year-old woman with a giant left internal carotid artery aneurysm causing visual symptoms underwent treatment with coiling, Surpass Evolve flow diverter placement, and balloon angioplasty. Despite being on dual antiplatelet therapy, she developed in-stent thrombosis on postoperative day 4, leading to neurological symptoms. Intra-arterial thrombolysis with eptifibatide and tenecteplase achieved near total recanalization and initial clinical improvement. However, she subsequently developed a massive subarachnoid hemorrhage and was declared brain dead the next day.

Conclusion

Delayed rupture of an aneurysm following Surpass Evolve flow diverter embolization is a rare complication associated with high morbidity and mortality. In our case, in-stent thrombosis occurred on postoperative day 4 and subsequently progressed to aneurysmal rupture, despite the presence of coils within the aneurysm sac. Rupture on the fourth day after Surpass Evolve flow diverter placement – despite initial coil embolization – along with aneurysmal thrombosis, partial recanalization, thrombus extension into the parent vessel, and subsequent treatment with intra-arterial eptifibatide and tenecteplase highlights the profound hemodynamic instability in giant aneurysms that can contribute to post-procedural rupture.

Introduction

Flow diverters significantly disrupt the inflow dynamics of an aneurysm, resulting in both qualitative and quantitative alterations to the intra-aneurysmal hemodynamic environment. Aneurysms that achieved complete or near-complete occlusion after treatment were statistically more likely to have smaller necks compared to those that remained partially patent [1]. Although a strong correlation has been observed between delayed aneurysm rupture and giant aneurysms, adjunctive coiling does not fully eliminate the risk. In fact, approximately 20% of delayed ruptures have occurred in aneurysms that were treated with additional coiling [2].

To better understand the mechanisms behind delayed aneurysm rupture following flow diversion, four clinical risk factors have been identified: large or giant aneurysms, symptomatic aneurysms, saccular aneurysms with an aspect ratio greater than 1.6, and inertia-driven inflow. The presence of fresh or organizing thrombus within the aneurysm lumen has also been associated with wall degeneration, increasing the risk of rupture. Inflammatory infiltration of the aneurysm wall has been shown to be an independent risk factor for rupture. However, it remains unclear whether postoperative aneurysm rupture after flow diversion with a pipeline embolization device is directly linked to intraluminal thrombus and associated inflammation. Some studies suggest that unstable, non-organized red thrombi may form due to immediate flow stagnation after flow diverter placement. These red thrombi, rich in proteolytic enzymes, can weaken the aneurysm wall. As the thrombus begins to organize, it may trigger further inflammatory responses within the wall, ultimately contributing to delayed aneurysm rupture [3].

Case Presentation

A 65-year-old woman with a history of hypertension presented with a chronic headache, complete vision loss in the left eye, and blurred vision in the right eye for the past 2 years. Imaging revealed a giant superior hypophyseal artery aneurysm of the left internal carotid artery (ICA), measuring 28 × 30 mm (Fig. 1). The aneurysm exerted a significant mass effect on the left supraclinoid ICA, leading to reduced flow in its distal branches compared to the contralateral side.

Fig. 1.

Giant superior hypophyseal artery aneurysm of the left ICA (a), after coil and flow diverter embolization (b), and on the 4th post-procedure day (c) with partial thrombosis of the aneurysm.

The patient was pre-treated with dual antiplatelet therapy consisting of clopidogrel and aspirin. Via a transfemoral approach, through a 10 Fr sheath, a 9 Fr, 80 cm Cook Shuttle, and a 125 cm, 5 Fr Stiff Simmons 2 catheter were advanced over a 0.035-inch stiff wire into the left common carotid artery. The guide catheter was navigated into the left cervical ICA, and the diagnostic catheter was removed.

Through Navien 058 catheter, an SL-10 microcatheter was advanced over a Synchro wire, and the “over-the-dome” technique was employed to catheterize the distal neck. The microcatheter was then advanced into the left inferior M2 segment, and the microwire was removed. An Asahi 018 wire was then introduced into the SL-10, and the microcatheter was exchanged. A Headway 27 was advanced over the Asahi wire into the left M2.

Next, a PX Slim catheter was advanced over an Aristotle 14 wire through the guide catheter into the left supraclinoid ICA, and the aneurysm was successfully catheterized. A Surpass Evolve 5 mm × 30 mm flow diverter was then delivered through the Headway 27. A PC-400 28 mm × 60 cm coil was subsequently advanced through the PX Slim, and a few loops were deployed within the aneurysm.

The flow diverter was then partially unsheathed and resheathed, with its distal tip placed in the left M2 segment. It was repositioned using the “pull and push” technique and then fully deployed. The initial coil was fully deployed, followed by the placement of an Axium Prime 13 mm × 50 cm filler coil.

A follow-up angiographic run demonstrated optimal positioning of the flow diverter from the mid M1 segment to the cavernous ICA. However, there was inadequate stent expansion at the proximal neck of the aneurysm, which was addressed with balloon angioplasty using a Gateway 3 mm × 15 mm balloon.

On postoperative day 4, the patient complained of headache. MRI revealed a small infarct in the left caudate head, although she remained neurologically intact. The following day, she experienced right-sided weakness and aphasia, which resolved significantly within 30 min. Brain MRI/MRA showed no new infarcts but revealed an occlusion of the left MCA M1 segment.

Given the unavailability of P2Y12 testing, clopidogrel resistance was suspected, and the patient was loaded with ticagrelor. Through a radial approach, angiography revealed a partially occlusive thrombus in the left M1 segment, extending from the distal end of the flow diverter to the mid-M1 segment. An initial attempt at thrombolysis with 5 mg of eptifibatide infused via microcatheter over 5 min was unsuccessful. Subsequently, 4 mg of tenecteplase was administered over 5 min, resulting in significant thrombus resolution, with only a small remnant beneath the flow diverter. Post-procedure, the patient showed marked clinical improvement, with no motor deficits and only mild naming difficulty.

Approximately 1 h later, she developed sudden bradycardia and a decline in consciousness. She was intubated and resuscitated. After hemodynamic stabilization, brain MRI revealed a modified Fisher Grade 4 subarachnoid hemorrhage (SAH) (Fig. 2). Despite supportive care, the patient was declared brain dead the following day and subsequently passed away.

Fig. 2.

a Thrombosed aneurysm on day 3 isointense on T1 (when the patient complained headache). b Small recanalization of the thrombus as compared to MRI taken a day prior. c FLAIR and SWI showing diffuse SAH.

Discussion

Delayed aneurysmal rupture after flow diverter deployment is an uncommon but serious complication of endovascular treatment, with pooled incidence estimates around 1–1.4% in large series and meta-analyses. Most delayed ruptures occur within the first 30 days following the procedure, often in large or giant aneurysms, and are associated with high morbidity and mortality rates. In a comprehensive literature overview, nearly 77% of delayed ruptures were observed within 1 month of flow diversion, and approximately 81% of those affected experienced death or poor neurological outcome. Giant aneurysms constituted nearly half of the delayed rupture cases, underscoring aneurysm size as a key risk factor. Additionally, intra-aneurysmal thrombus and posterior circulation location have been identified as significant predictors of delayed rupture in systematic analyses [2].

Flow-diverter devices (FDs) are advanced stents designed to be placed within the parent artery across the neck of an aneurysm. Their primary function is to disrupt blood flow into the aneurysm sac, producing significant hemodynamic changes and potentially altering the transmural pressure gradient. Over time, this flow disruption promotes progressive thrombosis within the aneurysm and facilitates the formation of neointima, providing long-term vessel wall reconstruction and aneurysm exclusion [4].

Delayed aneurysm rupture is among the most severe complications following flow diverter treatment, frequently resulting in SAH or carotid-cavernous fistula. The incidence of rupture after the procedure is approximately 4.0%, and the prognosis is often poor, with a combined mortality and neurological deficit rate of 81.3% [5]. Flow diverters rarely lead to immediate thrombosis and occlusion of an aneurysm. Instead, the healing process typically unfolds over days to months as the altered intra-aneurysmal flow gradually promotes thrombosis especially in patients receiving antiplatelet therapy. Persistent aneurysm patency following treatment has become a well-recognized challenge. Crucially, the exact degree of flow reduction required to trigger progressive thrombosis without leaving the aneurysm vulnerable to prolonged exposure or even an elevated risk of rupture remains unknown. At present, there are no reliable tools to accurately predict the thrombosis dynamics within treated aneurysms.

As a result, the clinical application of FDs continues to vary across institutions. One key difference lies in the number of devices used to treat a single aneurysm. Some centers prefer to implant only a single FD, anticipating that thrombosis will eventually develop regardless of the angiographic appearance of residual intra-aneurysmal flow. In contrast, other centers opt for multiple overlapping devices, deploying additional layers until a visually satisfactory reduction in flow – indicated by contrast stagnation – is achieved [6]. In an untreated aneurysm, blood enters during both systole and diastole, strongly impacting the distal wall and generating a counterclockwise flow pattern within the sac, driven by both pressure and shear forces. The placement of a conventional stent reduces the velocity gradient and weakens the inflow jet, though it does not fully eliminate it. In contrast, a flow diverter significantly restricts blood entry at the aneurysm neck, greatly lowering shear stress transmission and effectively eliminating the inflow jet on the distal wall. This also results in an increased pressure gradient along the parent vessel, driving blood into the aneurysm at the distal end and out at the proximal end [7].

Flow diverter treatment alone carries a potential risk of fatal rupture, particularly in large and giant aneurysms. This risk is heightened when the redirected blood flow continues to impact the aneurysmal dome, the common rupture site along the vessel wall. It is believed that thrombus formation during the healing process may actually weaken the aneurysm wall. This is because the wall remains exposed to pulsatile blood flow and the effects of an unstable red thrombus, which is rich in proteolytic enzymes and biologically fragile. To mitigate this risk, loose coil packing is sometimes used alongside FD placement. This adjunctive technique aims to accelerate thrombosis while also providing immediate mechanical support to the aneurysm dome during the early phase before complete thrombosis occurs [8]. In our cases, we have packed the aneurysm with coil, but there are other factors contributing for the delayed aneurysmal rupture and there are reports with similar flow diverter with coil and delayed rupture as reported by Rehman et al. [9] from USA. Previous studies have proposed 2 main hypotheses to explain aneurysm rupture following FD treatment [1]: increased intra-aneurysmal pressure and [2] inflammation triggered by thrombus formation [8].

Computational hemodynamic analyses have shown that aneurysm pressure can rise after FD placement, particularly in cases that later experienced rupture. By comparing computational fluid dynamics (CFDs) models of aneurysms before and after treatment in both ruptured and unruptured cases, there are two possible mechanisms for this pressure increase: the first is in aneurysms with proximal parent artery stenosis, FD deployment can alter vessel geometry and improve blood flow, inadvertently increasing pressure within the aneurysm and the second is FD placement may raise peripheral vascular resistance, triggering systemic autoregulatory responses that elevate systolic blood pressure, thereby increasing pressure inside the aneurysm.

FD placement increased aneurysmal resistance and reduced inflow. Aneurysms with wide necks, which permit more blood entry, tend to have higher resistance and are more likely to trigger autoregulatory pressure responses. An additional theory, supported by histopathological evidence, suggests that inflammation resulting from thrombus formation may weaken the aneurysm wall. Studies have documented autolysis of the aneurysmal wall, including fibroblast loss and necrosis, along with infiltration of acute inflammatory cells near rupture sites. When comparing the two mechanisms, ruptures due to elevated intra-aneurysmal pressure typically occur early within the first week after treatment while ruptures associated with inflammatory degeneration tend to happen later, usually between 1 week and 1 month post-procedure [10]. Our case appears to fall somewhere between the 2 proposed mechanisms. In relation to increased intra-aneurysmal pressure, we deployed a flow diverter to alter the vessel geometry and performed angioplasty using a Gateway balloon, which further impacted the parent artery’s geometry and peripheral vascular resistance. Together, these interventions likely enhanced blood flow and increased the intra-aneurysmal pressure gradient. The second hypothesis delayed rupture is due to inflammation triggered by partial thrombosis also applies to our case. On postoperative day 4, DSA revealed partial thrombosis within the aneurysm. Additionally, intra-arterial administration of eptifibatide and tenecteplase may have exacerbated the underlying pathological process by enhancing local platelet inhibition and fibrinolysis, thereby further compromising aneurysm wall stability and potentially precipitating the subsequent massive SAH. The other mechanism for delayed rupture as described by Fox et al. [11] is mechanical stretch on the vessel and stress at the weak point to result in vessel/aneurysm rupture [9, 11]. The presence of early thrombosis on the day 3 MRI followed by partial thrombosis on the day 4 MRI indicates significant hemodynamic instability within the aneurysm. There is limited literature available, with the reported risk of delayed rupture following Surpass Evolve placement being approximately 3% as compared with pipeline [12].

Conclusion

Flow diverters are stents designed to redirect blood flow away from aneurysms, promoting thrombosis and vessel healing. However, delayed aneurysm rupture remains a serious complication, particularly in large or giant aneurysms, with an incidence of ∼4% and high mortality. Rupture mechanisms include increased intra-aneurysmal pressure due to altered vessel geometry or peripheral resistance and inflammation triggered by thrombus formation. Red thrombi, rich in proteolytic enzymes, may weaken the aneurysm wall during the healing phase. Adjunctive coiling is often used to provide early structural support, but rupture can still occur. In our case, both pressure-related and inflammatory mechanisms likely contributed as partial thrombosis and thrombolytic use preceded a fatal SAH. Mechanical wall stress is another proposed factor in delayed rupture. The administration of intra-arterial thrombolysis may have played a contributory role in the aneurysmal rupture. Lack of CFD study and post-mortem examination is the limitation of case report. Future investigations of giant aneurysms treated with flow diversion should integrate vessel wall imaging and CFDs to improve understanding of post-treatment hemodynamic and inflammatory changes. This case report was prepared in accordance with the CARE guidelines. The CARE checklist is provided as a online supplementary file (for all online suppl. material, see https://doi.org/10.1159/000551600).

Statement of Ethics

Ethical approval is not required for this study in accordance with local or national guidelines. Written informed consent was obtained from the patient’s next of kin for publication of the details of their medical case and any accompanying images.

Conflict of Interest Statement

The authors declare no competing interest.

Funding Sources

The authors report that no funding was received for this work.

Author Contributions

Mikael Aseged Shimekit: conceptualization, data curation, formal analysis, investigation, methodology, project administration, resources, software, supervision, validation, visualization, writing – original draft, writing – review and editing, and Data Availability Statement. Samuel Masresha Fetene and Wondwossen G Tekle: methodology, project administration, resources, software, supervision, validation, visualization, writing – original draft, writing – review and editing, and Data Availability Statement. Eskedar Belayneh, Kaleab Eticha, Michael Yirgalem, Eden Zeleke, Bisrat Germame, Meti Taye, and Tariku Seboka: writing – original draft, writing – review and editing, and Data Availability Statement.

Funding Statement

The authors report that no funding was received for this work.

Data Availability Statement

The data that support the findings of this study are not publicly available due to privacy reasons but are available from the corresponding author upon reasonable request.