Case Report
The protocol for perioperative anticoagulant therapy was reviewed and approved by the institutional ethics committee/review board (approval number 05-11). Written informed consent was obtained from the patient before enrollment in this case report.
A patient in their 70s presented with an incidentally discovered unruptured cerebral aneurysm located at the right AChA during evaluation for headache. The aneurysm measured 12.2 mm in maximum diameter (Figure 1A and B). Although surgical treatment was initially considered, three-dimensional digital subtraction angiography revealed that the AChA originated from approximately the center of the aneurysm dome, creating a high risk of ischemic complications secondary to potential vessel occlusion during treatment (Figure 1C and D). Consequently, a conservative observation approach was initially adopted. However, follow-up magnetic resonance imaging suggested aneurysm enlargement, and the recent upgrade of our angiographic system enabled acquisition of higher-resolution images. Therefore, repeat cerebral angiography was performed to reassess aneurysm morphology and to reconfirm whether the AChA truly originated from the aneurysm sac. The aneurysm demonstrated progressive growth, with the maximum diameter increasing to 14.1 mm, indicating an elevated risk of rupture and necessitating definitive intervention (Figure 2A-D). Given the large size of the aneurysm and the incorporation of a branching vessel arising from its dome, this lesion was considered exceptionally challenging to treat because persistent outflow through the branch vessel would impede aneurysm thrombosis.
To minimize blood flow into the aneurysm as much as possible, a treatment strategy involving overlapping placement of 2 flow diverters across the aneurysm neck was employed. Additionally, given the extremely high risk of AChA occlusion associated with dense coil packing within the aneurysm sac, we limited coil deployment to the minimum necessary volume to facilitate thrombosis while maintaining AChA patency. Dual antiplatelet therapy (DAPT) consisting of prasugrel 3.75 mg and aspirin 100 mg daily was administered for 7 days preoperatively. Platelet function testing using the VerifyNow assay (Accriva Diagnostics, San Diego, CA, USA) was performed 2 days before the procedure. The results demonstrated a P2Y12 reaction unit of 81 and an aspirin reaction unit of 388, indicating adequate platelet inhibition.
The neuroendovascular procedure was performed via a transradial approach utilizing a 7-French Rist guide catheter (Covidien/Medtronic, Irvine, CA, USA). A Phenom 17 microcatheter (Covidien/Medtronic, Irvine, CA, USA) was first navigated into the aneurysm sac. An Axium Prime Frame 14 mm× 50 cm coil (Covidien/Medtronic, Irvine, CA, USA) was deployed in a loose configuration within the aneurysm to serve as a scaffold for thrombosis (Figure 3A). Subsequently, the first Pipeline Shield flow diverter (Covidien/Medtronic, Irvine, CA, USA), measuring 5 mm× 25 mm, was deployed from the M1 segment of the middle cerebral artery, proximal to the origins of the lenticulostriate perforating branches, extending across the aneurysm neck (Figure 3B). Following deployment of the first flow diverter, a Phenom 27 microcatheter (Covidien/Medtronic, Irvine, CA, USA) was navigated distal to the first Pipeline Shield. A second Pipeline Shield measuring 5 mm× 18 mm was then deployed from proximal to the origin of the A1 segment of the anterior cerebral artery, extending proximally to create an overlapping, telescoping configuration with the first flow diverter at the aneurysm neck. Percutaneous transluminal angioplasty was then performed using a Scepter C 4 mm× 11 mm balloon catheter (MicroVention, Tustin, CA, USA) along the entire length of both flow diverters, proceeding sequentially from distal to proximal segments, to improve device-vessel wall apposition and metal coverage at the aneurysm neck (Figure 3C-E). High-resolution cone-beam computed tomography was performed using the angiography system to confirm proper wall apposition of both flow diverters to the parent vessel. Postoperatively, intravenous argatroban was administered for 2 days. Oral anticoagulation with rivaroxaban 10 mg daily was initiated on postoperative day 1 and continued for 30 days, in addition to continuation of DAPT.
At 12-month follow-up cerebral angiography, the aneurysm demonstrated significant size reduction with near-complete occlusion of the aneurysm (Figure 4A and B). Notably, the origin of the AChA had migrated considerably toward the aneurysm neck region, and the aneurysm itself demonstrated only minimal residual contrast opacification at the neck (Figure 4C and D). This angiographic result was classified as O'Kelly-Marotta (OKM) grade C (contrast stasis with incomplete filling) subtype 3 (>95% occlusion). No new neurological deficits were observed during the perioperative period or during follow-up. Furthermore, magnetic resonance imaging demonstrated no evidence of new ischemic lesions, confirming preservation of the AChA territory.
Discussion
The principal observation of this case is the successful treatment of a high-risk AChA aneurysm-with the AChA arising directly from the aneurysmal sac-using overlapping flow diverters with loose coiling combined with modified triple antithrombotic therapy (DAPT plus reduced-dose direct oral anticoagulant for 30 days). This strategy achieved near-complete aneurysm occlusion (OKM grade C3) while preserving AChA patency. Critically, during gradual aneurysmal shrinkage, the AChA origin progressively migrated toward the aneurysm neck, enabling branch preservation while the sac underwent organized thrombosis. This observation addresses a major therapeutic challenge: aneurysms with branches arising from the sac present conflicting treatment requirements (aneurysm occlusion versus branch preservation) and carry the highest risk of ischemic complications.8-10)
The controlled thrombosis strategy-balancing mechanical flow diversion with pharmacological modulation-overcomes limitations of conventional approaches. Surgical clipping is associated with approximately 9% ischemic complications,2,11) while flow-diverter placement alone often fails to achieve complete occlusion when branch flow prevents thrombosis.7,12) This specific strategy has not been previously reported. Hosoo et al.7) described AChA occlusion due to rapid thrombosis after flow diverter placement with coiling-the very complication our approach aimed to prevent. Prior reports have noted incomplete occlusion with long-term anticoagulation,13) but none described a deliberate, time-limited approach for branch preservation. This represents a novel paradigm: controlled, gradual occlusion leveraging vascular remodeling rather than relying on acute treatment.
AChA aneurysms
Cerebral aneurysms arising at the AChA bifurcation account for approximately 2%-5% of all cerebral aneurysms and represent a relatively rare anatomical location.14) Most are located near the distal portion of the posterior communicating artery, arising from the internal carotid artery in proximity to the AChA origin. This anatomical relationship increases the risk of vascular compromise during treatment. Although some remain unruptured, rupture can result in subarachnoid hemorrhage with severe outcomes.
Several studies have attempted to classify AChA aneurysms based on the vessel's site of origin.8-10,15) Broadly, 3 subtypes have been described: those in which the AChA arises directly from the internal carotid artery near the aneurysm, those arising from the aneurysm neck, and those originating from the aneurysm dome. Across all reports, aneurysms from which the AChA originates from the sac are consistently recognized as carrying the highest risk of ischemic complications during treatment.8-10,15,16) In such cases, achieving both aneurysm occlusion and branch preservation remains a major therapeutic challenge.
Treatment options and comparative outcomes
Three principal modalities are available for the treatment of AChA aneurysms. Surgical clipping achieves the highest complete occlusion rates (approximately 85%),2) but intraoperative injury to the AChA may cause devastating sequelae, including hemiplegia, sensory deficits, and visual field deficits, with overall complication rates of approximately 17% and ischemic complication rates of roughly 9%.2,11) Endovascular coiling is a minimally invasive procedure with lower ischemic complication rates (approximately 3%), but inferior occlusion rates (74%) compared to clipping, often necessitating retreatment.2)
Flow-diverter therapy for AChA aneurysms demonstrates superior therapeutic efficacy and a significantly improved safety profile compared with conventional treatment modalities. Systematic reviews reveal that flow diversion achieves complete occlusion rates of approximately 80%, which compares favorably with coiling alone (75.3%) and is like surgical clipping (84.5%).2,8) The safety profile of flow diverter treatment is remarkably favorable, with ischemic complication rates ranging from 0.7% to 4.2%2)-a substantial reduction compared to surgical clipping (9.4%) and coiling procedures (3.0%). The low incidence of symptomatic AChA occlusion following flow diverter deployment is particularly encouraging, given the devastating neurological consequences of AChA territory infarction from infarction of the posterior limb of the internal capsule, optic radiation, and pyramidal tract.4,17-19)
When the AChA arises directly from the internal carotid artery or from the aneurysmal neck, flow diverter placement across the parent vessel may effectively "jail" the AChA without compromising its patency, while most aneurysms in these configurations achieve occlusion. In contrast, when the AChA arises from the aneurysmal sac itself, the hemodynamic demands of the branch often prevent complete thrombosis, making aneurysm occlusion less likely.7,12) Moreover, when aneurysm occlusion is achieved in this configuration, there is a substantial risk that the AChA will thrombose simultaneously, resulting in ischemic complications.7) Thus, in aneurysms where the AChA arises from the sac, treatment becomes particularly challenging, as both aneurysm occlusion and AChA preservation must be simultaneously achieved despite their inherently conflicting requirements.
Treatment strategy rationale
Our case involved a rare aneurysm with the AChA arising from the center of the aneurysm sac, which demonstrated rapid enlargement. Direct clipping or dense coil packing was expected to cause ischemia due to AChA occlusion. After thorough discussion, we selected an endovascular approach with overlapping flow diverter deployment and adjunctive loose coiling. The strategy emphasized 2 key principles: maximization of mechanical flow diversion and pharmacological control of aneurysmal thrombosis.
Maximization of mechanical flow diversion
Aneurysms with branch vessels arising from the sac are particularly difficult to treat, as intra-aneurysmal flow is necessary to maintain branch outflow.7,12) As a result, intra-aneurysmal flow reduction may be insufficient to promote thrombosis and complete occlusion. Computational fluid dynamics studies have demonstrated that overlapping multiple flow diverters can significantly reduce intra-aneurysmal flow velocity and promote thrombosis.20,21) Therefore, 2 overlapping flow diverters were deployed across the neck to enhance flow diversion and promote thrombosis.20,22) Although overlapping flow diverters are often avoided at initial treatment due to concerns about ischemic complications, the literature suggests that delayed overlapping as a retreatment strategy after incomplete occlusion is associated with lower aneurysm occlusion rates. Lauzier et al.23) reported that aneurysms treated with a single flow diverter achieved complete occlusion in only 26% of cases, even after subsequent overlapping deployment. The low effectiveness of delayed overlap retreatment supports our approach of applying sufficient treatment intensity at the initial procedure rather than relying on staged reinforcement.
Coil-assisted flow diverter placement was also chosen, as it has been reported to improve early complete occlusion compared with flow diverter placement alone.24) The aneurysm in our case demonstrated rapid interval enlargement over a short period, raising concern about the potential risk of delayed rupture following flow diversion. Although the protective effect of adjunctive coiling against post-flow diverter rupture has not been definitively established, and delayed rupture has been reported even after adjunctive coil placement,25) prior observational reports have suggested that adjunctive coils may facilitate earlier intra-aneurysmal thrombosis in selected aneurysm morphologies.24) Given that accelerated thrombosis could theoretically shorten the period during which rupture risk is highest, limited coil use was considered a reasonable adjunctive measure in this context.
However, because the AChA arose directly from the aneurysm sac, a conservative strategy was necessary to avoid thromboembolic events, which have been associated with excessive coil packing or manipulation in branch-incorporated aneurysms.26) Balancing these considerations, we elected to deploy only a single minimal coil, with the intent of modestly promoting early thrombosis while minimizing the risk of procedure-related ischemic complications involving the AChA territory.
Pharmacological control of thrombosis
This overlapping flow diverter with coil strategy carries a high risk of branch vessel occlusion due to rapid aneurysmal thrombosis. Hosoo et al.7) reported a similar case in which rapid thrombosis after flow diverter placement with coiling led to AChA occlusion. To mitigate this risk, we adopted triple antithrombotic therapy, adding a direct oral anticoagulant to conventional DAPT. This approach aimed to promote gradual thrombus formation, allow stepwise AChA adaptation, preserve branch patency, and ultimately achieve complete aneurysm occlusion through progressive remodeling.27)
Triple antithrombotic therapy effectively suppressed excessive acute thrombosis, and gradual aneurysm contraction was observed on follow-up imaging. Importantly, during the process of aneurysmal shrinkage, the origin of the AChA progressively migrated toward the aneurysmal neck. This anatomical shift permitted sustained patency of the AChA while most of the aneurysmal sac underwent organized thrombosis, thereby preventing ischemic complications in the AChA territory. This gradual occlusion strategy appears effective for aneurysms with branch vessels arising from the sac.
Critical role of postoperative antithrombotic therapy adjustment
Previous reports have noted incomplete aneurysm occlusion in patients receiving long-term anticoagulation after flow diverter placement.13) We hypothesized that short-term anticoagulation could prevent rapid occlusion of the aneurysm and associated branch vessel compromise while still permitting eventual complete occlusion. However, because DAPT is mandatory for flow diverter placement, the addition of anticoagulation results in triple therapy, which carries a high hemorrhagic risk.27)
The PIONEER-AF PCI trial demonstrated that lowering direct oral anticoagulant doses and minimizing duration significantly reduces hemorrhagic complications,28) and the Japanese Circulation Society guidelines recommend limiting triple therapy to the shortest feasible duration.29) Accordingly, we administered rivaroxaban at 10 mg (below the standard dose of 15 mg) for 30 days. This regimen avoided postoperative hemorrhagic complications such as aneurysm rupture while preserving AChA patency, allowing gradual thrombosis, aneurysm shrinkage, and eventual OKM grade C3 occlusion. Although short-term, low-dose anticoagulation combined with DAPT was effective in this case, additional clinical experience is needed to establish the optimal antithrombotic regimen for safe aneurysm occlusion.
Apparent translocation of the AChA origin after flow diversion
In aneurysms in which the AChA originates from the central portion of the aneurysm dome, flow diverter treatment may result in an apparent shift of the AChA origin toward the aneurysm neck during follow-up. This finding does not indicate true migration of the branch vessel but rather reflects dynamic aneurysm remodeling. After flow diversion, neointimal formation across the aneurysm neck progressively reduces inflow to the sac, whereas continuous flow demand through the incorporated AChA preserves a localized flow channel. As thrombosis and volume reduction proceed in the remaining aneurysm, the residual lumen becomes confined to the vicinity of the branch ostium, creating an infundibulum-like configuration or a proximal AChA course that appears closer to the parent artery. This process is consistent with the concept of branch-incorporated aneurysm remodeling and may represent a stable or progressive remodeling pattern rather than incomplete occlusion.
Limitations and future directions
The principal limitation of this report is that it describes a single case experience. The optimal perioperative anticoagulation strategy, including appropriate dosing and duration of therapy, has not been definitively established. The optimal strategy regarding adjunctive coiling and the use of overlapping flow diverters remains to be determined. Flow diverters with increased metal coverage density may achieve stronger flow diversion with a single device, potentially reducing the need for overlapping deployment, which has been associated with an increased risk of ischemic complications. Further case accumulation and systematic study are needed to refine treatment protocols for similar complex aneurysms with branch vessel incorporation. Additionally, long-term follow-up data are required to assess the durability of aneurysm occlusion and sustained branch patency.
In this case involving an AChA aneurysm with the artery arising from the aneurysm sac, intensive treatment combining overlapping flow diverter deployment with adjunctive coiling and modified triple antithrombotic therapy achieved near-complete aneurysm occlusion while preserving branch vessel patency. This treatment strategy may serve as a valuable option for AChA aneurysms with sac-originating branches, which have traditionally been considered challenging to treat. The gradual occlusion strategy utilizing pharmacological thrombus control represents a novel approach that reduces acute-phase branch occlusion risk and enables stepwise vascular adaptation. Future accumulation of cases and evaluation of long-term outcomes will be necessary to validate this approach.
