INTRODUCTION
Extracranial carotid artery aneurysms (ECAAs) are rare; they account for less than 1% of all arterial aneurysms and 0.1–2.0% of all carotid artery operations. This could be due to the fact that these types of ECAAs frequently go untreated; they seldom rupture but are associated with a higher risk of thromboembolic events in the nervous system, which can eventually result in cranial nerve damage [1,2].
The management of large extracranial aneurysms remains controversial, not only regarding whether the lesion should be touched but also concerning the choice of treatment modality [2]. Surgical resection can be considered in selected cases. However, surgery may be technically demanding in high cervical and skull base locations, and there are additional hazards related to surgery [3]. Moreover, endovascular treatment may be performed; there are reports on coil embolization and the use of covered stents and trapping of the parent artery. Covered stents and stent grafts are an alternative, particularly in urgent settings; however, their use is limited by stiffness, difficulty navigating tortuous carotid anatomy, and a lack of dedicated devices [4].
While the concept of using flow diversion is appealing for large aneurysms, the application of primary flow diverters in extracranial carotid lesions may face restrictions due to off-label use, reimbursement challenges, and factors related to the devices themselves [5,6].
Therefore, multiple overlapping stents were evaluated as a pragmatic reconstructive alternative to achieve flow diversion. The braided stent, such as the new Low-profile Visualized Intraluminal Support (LVIS® D) (LVIS blue) (MicroVention), provides sufficient flow diversion on ECAA, as its metal coverage is greater than that of conventional flow diverters. In this case series, we describe our experience adopting this method.
CASE SERIES
All neurointerventional procedures for patients diagnosed with ECAA treated with overlapping LVIS stents in our institution between 2007 and 2022 were analyzed.
Five patients with large or clinically significant ECAAs were treated using multiple overlapping LVIS stents and met our inclusion criteria, which were as follows: (1) symptomatic ECAAs and (2) asymptomatic ECAAs treated owing to substantial size, expansion, thromboembolic risk, or compressive potential observed on imaging.
The ECAAs locations were found in 3 segments: (1) proximal (carotid bulb to midway distance from petrosal internal carotid artery [ICA] segment), (2) distal (petrosal ICA segment), and (3) middle (midway between the carotid bulb and petrosal segment).
Detailed clinical characteristics, aneurysm morphology, procedural devices, and follow-up outcomes are summarized in Tables 1 and 2. Because the treatment course was relatively straightforward in 4 patients and highly staged in 1 patient, the overall cohort is first summarized, followed by a detailed description of the most complex case.
All procedures were performed under local anesthesia and systemic heparinization. The patients were premedicated with dual antiplatelets (aspirin and clopidogrel) at least 5 days before the procedure. After diagnostic angiography and parent-artery measurement, a microcatheter was advanced across the aneurysm segment. LVIS stents were deployed in an overlapping fashion across the aneurysm neck or diseased segment. The number, size, and overlapping extent of stents were determined according to aneurysm morphology, parent-artery diameter, neck configuration, wall apposition, and immediate angiographic flow response. When residual inflow, incomplete wall apposition, stenosis, or insufficient flow modification was observed, adjunctive or staged treatment was considered.
A separate publication from our institution addressed a different research question using a subset of the patients included in this study. With unique goals, methodology, and measures, the current study is an independent investigation [3].
The cohort consisted of 4 females and 1 male, with a mean age of 60 years. The aneurysms were located in the cervical or petrous ICA segments and ranged from 12 mm to 42 mm in maximal dimension. Treatment was performed due to symptoms, substantial aneurysm size, compressive potential, thromboembolic concern, or concern regarding future progression on imaging. Double overlapping LVIS stents were used in 3 cases, whereas triple or more extensive overlapping constructs were used in 2 cases.
Immediate angiography showed intra-aneurysmal flow reduction with preserved parent-artery patency in 3 cases, whereas 2 cases showed insufficient flow reduction or parent-artery stenosis. During a mean radiologic follow-up of 24 months, complete aneurysm occlusion was achieved in 2 cases, and residual aneurysmal filling persisted in 3 cases. No major thromboembolic or hemorrhagic complication was documented. Multiple adjunctive or staged treatments were required in 3 cases, including balloon angioplasty, additional LVIS stenting, flow-diverter placement, stent-graft placement, and/or coil embolization.
In 4 of the 5 cases, the treated lesions showed relatively stable follow-up courses, although residual filling was observed in 2 cases. In case 1, double overlapping LVIS stents resulted in immediate flow reduction, and 3-year computed tomography angiography (CTA) demonstrated only minimal residual filling. In case 2, double overlapping stents similarly reduced aneurysmal inflow, but a small residual sac remained on the 2-year magnetic resonance angiography (MRA). In case 4, triple overlapping stents led to progressive thrombosis and complete occlusion on the 3-year MRA. In case 5, flow reduction after double overlapping stent placement was insufficient, requiring adjunctive coil embolization during the same session; a small residual sac persisted on the 3-year MRA. By contrast, case 3 required staged escalation of endovascular manipulations due to persistent aneurysmal filling after the initial and successive treatments and is described separately below.
Representative Case
Case 3 was a patient in their 70s who was incidentally found to have a large, partially thrombosed right mid-cervical ICA aneurysm during evaluation for dizziness. The aneurysm measured 67×58×50 mm and was associated with tortuosity of the subpetrosal cervical ICA and distal parent artery narrowing due to the mass effect of the aneurysm sac. Because the lesion was large and conservative management was considered inappropriate, reconstructive endovascular treatment was planned. Primary flow-diverter placement was not selected because of off-label indication and reimbursement concerns for extracranial carotid use.
Initial treatment consisted of deployment of 3 overlapping LVIS stents (2 overlapped placements of 4.5x32 mm stents and then additional overlapped stenting with a 5.5x30 mm stent across the aneurysm orifice to maximize local metal coverage). Immediate angiography showed decreased but persistent intra-aneurysmal flow with improved parent artery patency. A 6-month-CTA demonstrated persistent aneurysmal filling together with an intra-luminal filling defect within the stent. Successive retreatment was done with angioplasty using a 4-mm-diameter balloon catheter (Aviator; Boston Scientific) followed by additional overlapping LVIS stent placement (5.5x30 mm).
Despite these staged reconstructive procedures, persistent inflow into the aneurysm was noted on 1-year follow-up. A flow diverter (Pipeline Embolization Device, 5x35 mm; Medtronic) was subsequently placed as an off-label escalation treatment. However, successive CTAs obtained at 6- to 12-months intervals repeatedly revealed persistent aneurysm filling even with an increase in aneurysm volume, resulting in neck discomfort and swallowing difficulty on 3-year follow-up. Considering the equivocal decrease in collateral status on ipsilateral carotid occlusion stent, we decided to perform stent graft implantation since the endoleaks were focal. Stent-graft placement was done with the telescopic stenting of 2 stent grafts (Jo Stentmaster RX stent, 3.5x26 mm and 4.0x19 mm; Abbott Vascular), requiring an additional stent at the very proximal segment (4.0x19 mm), resulting in complete occlusion initially. The aneurysm stayed stable without recurrence on her latest CTA follow-up performed 1.5 years postoperatively (Fig. 1). This case illustrates that increasing metal coverage with overlapping braided stents may not always translate into effective flow diversion in a large, partially thrombosed aneurysm with tortuous parent-artery anatomy.
DISCUSSION
Pathophysiology and Prevalence of Large Extracranial Carotid Artery Aneurysms
ECAAs are considered to be rare and might have heterogeneous etiology such as atherosclerosis, trauma, infection iatrogenic after neck surgery, and radiation. However, in real practice, some times a definitive etiology cannot be identified, especially in isolated ECAA without preceding any of these mentioned causes. Although rupture is uncommon, large ECAAs still needed to be treated owing to substantial size, expansion, thromboembolic risk, or compressive potential observed on imaging [7-10].
Available Treatment Options
Management with antithrombotic medical therapy still plays a role in selected cases, such as extracranial carotid dissections. Surgical resection can be considered in selected cases as the main line of treatment. However, surgery may be technically demanding in high cervical and skull base locations and hazards related to surgery and hostile neck conditions. Moreover, endovascular treatment may be done due to their lower procedural morbidity and faster recovery. Therefore, reconstructive endovascular treatment is often considered in lesions that are surgically inaccessible or unsuitable for parent-artery sacrifice [2-4].
Endovascular Treatment and the Flow-Diversion Concept
Coil embolization remains an option but carries a risk of recanalization and may worsen mass effects in large aneurysms. Covered stents or stent-grafts are an alternative, particularly in urgent settings; however, their use is limited by stiffness, difficulty navigating tortuous carotid anatomy, and a lack of dedicated devices. There may be apprehensions about thromboembolic complications, especially when utilized beyond specific carotid indications [3,4].
The concept of using flow diverters is appealing for large aneurysms; they reconstruct the parent artery and promote progressive intra-aneurysmal thrombosis. However, the application of primary flow diverters in extracranial carotid lesions may face restrictions due to off-label use, reimbursement challenges, and factors related to the devices themselves [5,9,10]. These real-world limitations create a therapeutic gap between conservative management and ideal reconstructive flow diversion.
Rationale for Multiple Overlapping LVIS Stents under Real-World Constraints
In addition to favorable clinical and angiographic outcomes, the hemodynamic effectiveness of overlapping intracranial stents has been supported by in vitro and computational studies [11,12]. Studies have demonstrated that double or triple LVIS configurations achieve metal coverage comparable to conventional flow diverters. Also, that metal coverage can be increased by stent compaction or overlapping [13].
The rationale of the present case series was not that overlapping LVIS stents should replace flow diverters in all large extracranial carotid aneurysms. Rather, our treatment strategy arose from a practical dilemma. From a purely anatomical and hemodynamic standpoint, large or giant aneurysms are natural candidates for flow-diversion therapy. However, when such aneurysms are located in the extracranial carotid artery, off-label indication and medical insurance reimbursement issues may restrict the use of conventional flow diverters. In this setting, multiple overlapping LVIS stents may provide a pragmatic reconstructive alternative.
Because LVIS is a braided stent with relatively high metal coverage, overlapping or compacting multiple LVIS stents can theoretically increase local metal coverage to a level comparable to, or in selected configurations even higher than, that achieved by conventional flow diverters [11,12]. Therefore, we considered overlapping LVIS stenting a reasonable strategy to bridge the gap between conservative management and off-label flow-diverter therapy. In this sense, our approach was not merely a compromise forced by device limitations but a mechanistically plausible strategy adapted to the realities of extracranial carotid aneurysm treatment.
Our experience, however, suggests that this strategy has both strengths and limitations. The procedure was technically viable, and no significant thromboembolic or hemorrhagic complications were noted in this small cohort. However, aneurysm occlusion was not consistently achieved. Complete occlusion was realized in only a few cases, while in others, there was a need for persistent residual filling or staged retreatment. Therefore, overlapping LVIS stents are feasible and safe for extracranial aneurysms yet have limited standalone efficacy, particularly in large or complex aneurysms, often requiring adjunctive or staged treatment.
Metal Coverage Alone May be Insufficient Element
In case 3, a lesson was learned, increasing metal coverage alone is not sufficient in complex large ECAAs. This aneurysm was large, partially thrombosed, and located along a tortuous mid-cervical to subpetrosal ICA segment with distal parent-artery narrowing. In such anatomy, the theoretical metal coverage of overlapping stents may not translate into uniform effective coverage at the aneurysm neck. Incomplete wall apposition, gaps between stent layers, nonuniform stent expansion along the curved parent artery, persistent inflow channels within a partially thrombosed sac, and progressive intimal hyperplasia or restenosis may all reduce the intended flow-diversion effect.
The eventual need for off-label flow-diverter placement and stent-graft escalation in this case suggests that some lesions behave not as focal aneurysmal outpouchings but as diseased arterial segments requiring a stronger reconstructive or even destructive strategy. Therefore, applying overlapping LVIS stenting indiscriminately to all large extracranial aneurysms may be imprudent. Complex aneurysms require early recognition of adverse anatomical features and should be managed with a clear escalation plan from the outset.
Future Treatment Strategy for Similar Patients
Based on this series, our future approach should be lesion-specific rather than device-specific. Multiple overlapping LVIS stents may still be a viable reconstructive option for large ECAAs in patients whom conservative therapy is deemed inadequate due to factors such lesion size, growth, thromboembolic risk, or compressive potential.
Especially when the goal is to gradually reduce flow while maintaining the ICA, the aneurysm has a well-defined neck, or the parent artery is not extremely tortuous, proper overlapping, pull-push compaction, and stent size grading can enhance flow diversion of the aneurysm [13-15]. This strategy may be especially relevant in practice environments where primary flow-diverter use is limited by off-label indication or reimbursement restrictions.
However, we should be cautious about applying the same strategy indiscriminately to all large extracranial aneurysms. In complex aneurysms, including giant, partially thrombosed, fusiform, long-segment, or markedly tortuous lesions, overlapping LVIS stenting alone may be insufficient. In such cases, open surgical intervention should be considered first when the lesion is surgically accessible, and the expected morbidity is acceptable [3]. If surgical repair is difficult because of high cervical, subpetrosal, or skull-base location, destructive endovascular treatment such as trapping or parent-artery occlusion may be considered when collateral circulation is adequate [4,6]. When parent-artery preservation is necessary and a reconstructive strategy is preferred, primary off-label flow-diverter treatment may be more appropriate than repeated overlapping conventional stenting in selected patients, provided that the regulatory, reimbursement, and clinical risks are carefully discussed [16]. If overlapping LVIS stents are selected initially, early follow-up angiography should be planned, and persistent inflow, restenosis, or progressive mass effect should prompt timely escalation rather than repeated passive observation.
Limitations
There are limitations related to our study. First, it is a small retrospective case series from a single institution. Second, the aneurysms were heterogeneous in size, location, morphology, etiology, and treatment indication. Third, the procedural strategy was not standardized, and adjunctive or staged treatments were performed according to angiographic findings and clinical judgment. Fourth, follow-up imaging modalities were not uniform. Finally, because this study was conducted in a real-world practice setting influenced by device indication and reimbursement constraints, the results should not be interpreted as a direct comparison between overlapping LVIS stents and dedicated flow diverters or covered stents. Rather, this series should be understood as an experience-based report on the potential role and limitations of overlapping LVIS stenting for large ECAAs when primary flow-diverter use is constrained. Larger multicenter studies are warranted.
CONCLUSION
Multiple overlapping LVIS stenting is a feasible and relatively safe reconstructive option for selected large ECAAs, particularly in practice settings where primary flow-diverter use is limited by off-label indication or reimbursement constraints. However, they have limited standalone efficacy, particularly in large or complex aneurysms, often requiring adjunctive or staged treatment. Careful lesion selection, early imaging follow-up, and a predefined escalation strategy—including surgery, parent-artery occlusion or trapping, off-label flow diversion, or stent-graft placement when appropriate—are essential.
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