Overlapping Flow Diverter with Coiling for Fetal-type Posterior Communicating Artery Aneurysms with Triple Antithrombotic Therapy: A Case Series

Abstract

Flow diverters have revolutionized the treatment of large and giant cerebral aneurysms. However, aneurysms with branch vessels originating from the aneurysm sac remain challenging for flow diverter monotherapy. We present five cases demonstrating favorable outcomes following combined treatment with overlapping flow diverter with coiling. The study cohort included five female patients with a mean age of 72.8 years. The mean aneurysm diameter was 8.1 mm. Triple antithrombotic therapy (dual antiplatelet therapy plus short-term anticoagulation) was administered to prevent ischemic complications due to posterior communicating artery occlusion in the perioperative period. Complete or near-complete occlusion (O'Kelly-Marotta grade C or D) was achieved in all cases. Follow-up angiography (mean follow-up time: 17.2 months) revealed preserved patency of the posterior communicating artery in four of five cases. In one case, the posterior communicating artery arising from the aneurysm was occluded at its origin but was supplied retrograde from the posterior circulation. Follow-up digital subtraction angiography of most cases showed caliber changes, with the posterior communicating artery diameter reducing and the P1 segment of the posterior cerebral artery increasing. No ischemic or hemorrhagic complications occurred perioperatively or during follow-up. Overlapping flow diverter with coiling combined with low-dose and short-term triple antithrombotic therapy might be a safe and effective treatment for fetal-type posterior communicating artery aneurysms, offering a viable alternative for complex aneurysms. Further studies with long-term follow-up data from a larger patient cohort are required to validate the efficacy and safety demonstrated in this case series.

Introduction

The clinical application of flow diverters (FDs) has dramatically transformed endovascular treatment of large and giant cerebral aneurysms.^1-3) These devices have demonstrated remarkable improvement in treatment outcomes for cases previously considered unsuitable for conventional coil embolization. While FDs represent an undoubtedly effective treatment modality for cerebral aneurysms, certain aneurysm characteristics have emerged as particularly challenging for FD monotherapy. Specifically, aneurysms with branch vessels originating from the aneurysm sac, such as fetal-type posterior communicating arteries,^4-6) demonstrate lower complete occlusion rates with FD monotherapy. In fetal-type posterior communicating artery (PComA) aneurysms, the increased hemodynamic demand for posterior cerebral artery (PCA) perfusion through the PComA results in persistent flow diversion into large-caliber collateral vessels following FD deployment. This phenomenon leads to inadequate reduction of intra-aneurysmal flow dynamics and subsequently impedes the progression of thrombotic occlusion.⁷⁾ Overlapping FD (OFD) at the aneurysm neck^8-10) and the combination of FD with coiling (FDC)^11,12) have both been reported to promote intra-aneurysmal thrombosis and improve aneurysm occlusion rates. We hypothesized that OFD with coiling (OFDC), combining both OFD and FDC strategies, might provide more potent therapeutic effects for PComA aneurysms. Previous studies have shown that anticoagulation after FD treatment significantly reduces aneurysm occlusion rates.¹³⁾ Based on this evidence, we propose that adding anticoagulation to conventional dual antiplatelet therapy (DAPT) (triple therapy) during the perioperative period may help prevent rapid intra-aneurysmal thrombosis, maintain PComA patency, and lower the risk of perioperative ischemic complications.

This is a preliminary case series of fetal-type PComA aneurysms managed with OFDC combined with triple therapy.

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 all participants before enrollment in this series. We defined a fetal-type PComA as an anatomical variant of the circle of Willis in which the PComA is relatively large and constitutes the primary source of blood flow to the PCA territory, while the proximal PCA segment (P1) arising from the basilar or vertebrobasilar system is small, hypoplastic, or absent.¹⁴⁾ Among eight patients with fetal-type PComA aneurysms treated at our institution between August 2020 and November 2023, five cases in which the PComA originated from the aneurysm dome were included in this study. Patients were eligible for this treatment if the PComA measured ≥1.2 mm in diameter, originated from the aneurysm dome, and the aneurysm was either 5-10 mm in size with recurrence after previous endovascular treatment or a large aneurysm (≥10 mm).

Five female patients with fetal-type PComA aneurysms underwent OFDC treatment at our institution. The mean age was 72.8 years, and the mean maximum aneurysm diameter was 8.1 mm. The cohort included patients with unruptured cerebral aneurysms and chronic recurrent cases following previous rupture. OFDC treatment was performed for five cases of PComA aneurysms. Clinical presentations varied across the cohort-two cases presented with symptomatic aneurysms manifesting as oculomotor nerve palsy before treatment. Two cases were recurrent aneurysms following coil embolization, and two were recurrences after stent-assisted coiling using the Neuroform Atlas (Stryker Neurovascular, Fremont, CA, USA). Additionally, two patients underwent retreatment for chronic-phase recurrence of previously ruptured cerebral aneurysms.

FRED (flow re-direction endoluminal device) (MicroVention, Tustin, CA, USA) was used in one case and Pipeline Flex Shield (Covidien/Medtronic, Irvine, CA, USA) in four cases.

DAPT with prasugrel 3.75 mg and aspirin 100 mg was administered for 7 days preoperatively. Platelet function testing (Verify Now: Accriva Diagnostics, San Diego, CA, USA) was performed 2 days before surgery, targeting P2Y12 reaction units (PRUs) of 60-180 and aspirin reaction units (ARUs) <550. Mean preoperative PRU was 132.6, and mean ARU was 427.2. All patients received 48-hour argatroban anticoagulation postoperatively. Direct oral anticoagulants (DOACs) were initiated on postoperative day 1, using Edoxaban 15-30 mg or rivaroxaban 10 mg orally for a mean duration of 28 days. DAPT was continued for approximately 6 months postoperatively, then switched to single antiplatelet therapy for maintenance. The characteristics of all cases described above are summarized in Table 1.

Table 1

Patient and Aneurysm Characteristics

Patient number	Aneurysm Maximum diameter	DOAC	Clinical presentation	Prior treatment	PRU	ARU	length of angiographic follow up (months)	OKM	Preoperative PComA size (mm)	post procedure PComA size F/U (mm)	Preoperative P1 size (mm)	post procedure P1 size F/U (mm)
ARU: aspirin reaction units; DOAC: direct oral anticoagulants; F/U: follow-up; NA: Not Applicable; OKM: O’Kelly-Marotta classification; PComA: posterior communicating artery; PRU: P2Y12-reaction units; SAC: stent assisted coiling; SAH: subarachnoid hemorrhage
1	12.6	Edoxaban 30 mg	SAH/oculomotor nerve palsy	clipping/coiling	171	546	32	C3	1.7	1.7	0.1	0.1
2	9.1	Edoxaban 30 mg	incidental	SAC	129	397	18	C3	1.7	0.6	0.1	0.1
3	10.2	Edoxaban 15 mg	incidental	NA	148	399	12	C3	1.2	Retrograde flow	1	1.6
4	5.7	Rivaroxaban 10 mg	SAH	coiling	121	398	12	D	1.8	0.3	1.3	1.3
5	7.2	Rivaroxaban 10 mg	oculomotor N palsy	SAC	94	396	12	D	2.1	0.8	0.1	1.1

All cases underwent endovascular treatment under general anesthesia with simultaneous FD overlap and coil embolization. Following sheath insertion, intravenous heparin (5,000 units) was administered, and the activated clotting time was maintained at 250-300 seconds. All procedures involved coil embolization of the aneurysm, followed by the sequential deployment of two FDs. The first FD was deployed with its distal end positioned proximally to the M1 perforating branches of the middle cerebral artery. The second FD was then deployed with its distal end placed at the distal internal carotid artery, proximal to the A1 origin when feasible, to achieve complete overlap of both devices across the entire aneurysm neck. Percutaneous transluminal angioplasty was performed after FD placement in all Pipeline cases to improve apposition between the parent vessel and FDs. Following overlapping flow diverter placement, high-resolution cone beam computed tomography (CT) with diluted contrast was performed to confirm proper apposition between the parent vessel and FDs, and overlap zone apposition. Procedures were concluded after puncture site hemostasis using vascular closure device (Perclose Pro Glide: Abbott Vascular, CA, USA). Embolization efficacy was evaluated using the O'Kelly-Marotta (OKM) classification through imaging follow-up. Branch vessel patency and neurological complications were assessed.

The diameters of the PComA and the P1 segment of the PCA were measured using source images from magnetic resonance angiography, CT angiography, or digital subtraction angiography (DSA). In this case series of five patients treated with OFDC, we achieved favorable embolization outcomes without hemorrhagic complications. No ischemic complications were observed during either the perioperative or follow-up periods in all cases. The mean DSA follow-up period was 17.2 months (range: 12-32 months). At the latest DSA follow-up, complete occlusion (OKM grade D) was achieved in two cases, while the remaining three cases demonstrated near-complete occlusion (OKM grade C3). At follow-up, DSA revealed occlusion of the PComA at its origin in one case; however, in this case retrograde perfusion from the posterior circulation was preserved. In all other cases, PComA remained patent, and no ischemic lesions were detected. Four of the five cases showed reduction of the PComA, and two cases demonstrated dilatation of the P1 segment. No instances of in-stent stenosis exceeding 50% or delayed hemorrhagic complications were observed.

Illustrative Cases

Case 2

A patient in their 70s presented with a severe headache. Magnetic resonance imaging (MRI) revealed an internal carotid artery-PComA junction aneurysm (maximum diameter 9.1 mm). The PComA originated from the aneurysm sac. The P1 segment of the PCA was hypoplastic on magnetic resonance angiography, making preservation of the PComA essential (Fig. 1A and B). Initial treatment involved the placement of a Neuroform Atlas stent (Stryker Neurovascular, Fremont, CA, USA) from the PComA to the proximal internal carotid artery, followed by stent-assisted coil embolization. However, an early major recurrence was observed postoperatively (Fig. 1C).

Figure 1

Overlapping Pipeline deployment for fetal-type posterior communicating artery aneurysm.

Preoperative right internal carotid artery angiography in oblique view (A) and 3D-DSA (B) show a 9.1 mm fetal-type posterior communicating artery aneurysm with 1.7 mm posterior communicating artery branching from the aneurysm. Follow-up angiography demonstrates significant coil compaction (C). Postoperative high-resolution cone beam CT shows an overlapping configuration of two Pipeline devices at the aneurysm neck (D). Follow-up angiography at 18 months demonstrates nearly complete aneurysm occlusion with markedly narrowed posterior communicating artery (E; black arrow).

3D: three-dimensional; DSA: digital subtraction angiography

For OFDC treatment, additional coils were placed in the compacted intra-aneurysmal coil mass, followed by the placement of Pipeline Shield 3.25 mm× 16 mm in the distal internal carotid artery via the existing Neuroform Atlas using a Phenom 27 catheter. A second Pipeline 3.25 mm× 16 mm was then overlapped within the first Pipeline (Fig. 1D). Follow-up DSA at 14 months demonstrated significant PComA diameter reduction with complete aneurysm occlusion (OKM grade C3) (Fig. 1E).

Case 3

A patient in their 70s was incidentally diagnosed with an unruptured cerebral aneurysm during brain MRI performed for evaluation of an unrelated condition. DSA revealed a PComA aneurysm measuring 10.2 mm in maximum diameter and, distally, an anterior choroidal artery aneurysm measuring 3.9 mm in maximum diameter, both arising from the left internal carotid artery (Fig. 2A). The PComA and anterior choroidal artery originated from the dome of their respective aneurysms, necessitating preservation of these branch vessels (Fig. 2B). Following induction of general anesthesia, a framing coil was placed under balloon-assisted technique to avoid covering the origin of the PComA with the coil loop. Without detaching the framing coil, a second microcatheter was navigated into the coil cage, and a total of five coils were deployed within the aneurysm using the double-catheter technique while preserving the PComA. Subsequently, a 4.0 mm× 18 mm Pipeline Shield was deployed from the M1 segment of the left middle cerebral artery to the internal carotid artery, followed by deployment of an additional 4.0 mm× 16 mm Pipeline Shield from just proximal to the A1 segment of the anterior cerebral artery to the internal carotid artery (Fig. 2C). At 12-month follow-up DSA, the PComA aneurysm had decreased in size (Fig. 2D and E), demonstrating OKM grade C3 occlusion while preserving flow to the origin of the PComA. In contrast, the anterior choroidal artery aneurysm treated with overlapped FDs only, without coil insertion, showed a slight reduction in size; however, persistent flow within the aneurysm sac was still observed.

Figure 2

Overlapping Pipeline treatment for tandem posterior communicating and anterior choroidal artery aneurysms.

Preoperative left internal carotid angiography shows a posterior communicating artery aneurysm (10.2 mm) and, at its distal, an anterior choroidal artery aneurysm (4.2 mm) (A). 3D-DSA lateral view demonstrates the posterior communicating artery originating from the aneurysm body (B). After loose coil placement, two overlapping Pipeline devices were deployed from M1 to proximal cavernous ICA, covering both aneurysm necks (C). Twelve-month follow-up angiography shows near-complete occlusion of the posterior communicating artery aneurysm with minimal residual flow at the posterior communicating artery origin (D). Follow-up 3D-DSA demonstrates preserved flow from the posterior communicating artery origin (E; white arrow), with a markedly diminished vessel (E).

3D: three-dimensional; DSA: digital subtraction angiography

Case 4

A patient in their 70s presented with a right PComA aneurysm incorporating the PComA. The patient initially presented with subarachnoid hemorrhage and underwent coil embolization; however, 21 months later, the aneurysm re-ruptured and was retreated. At the 18-month follow-up after the second procedure, DSA demonstrated coil compaction and aneurysm regrowth (Fig. 3A). Given the history of two prior subarachnoid hemorrhage episodes, a third treatment was performed. Following induction of general anesthesia, two coils were placed within the aneurysm sac (Fig. 3B). Subsequently, a 3.5 mm× 16 mm Pipeline Shield was deployed from the M1 segment of the middle cerebral artery to the internal carotid artery. A Pipeline of the same size was then deployed from just proximal to the anterior choroidal artery to overlap the aneurysm neck fully. High-resolution cone beam CT performed just after placement of both FDs revealed incomplete apposition of the devices to the internal carotid artery wall. Balloon angioplasty was performed using a Scepter C balloon 4 mm× 11 mm (MicroVention, Tustin, CA, USA) (Fig. 3C). At the 12-month follow-up, angiography demonstrated complete occlusion of the aneurysm, with the PComA visualized retrogradely via a small-caliber P1 segment of the PCA (Fig. 3D and E).

Figure 3

Recanalized posterior communicating artery aneurysm treated with additional coiling and overlapping Pipeline deployment.

Lateral right internal carotid angiography demonstrates coil compaction and significant recanalization of a posterior communicating artery aneurysm following two prior embolization procedures (A). Lateral DA image demonstrates additional coil placement at the compaction site (B). Two overlapping Pipeline devices were deployed from M1 to cavernous internal carotid artery and from proximal A1, followed by PTA (C). On 12-month follow-up, the lateral view left internal carotid angiography (D) and 3D-DSA (E) show that the posterior communicating artery was occluded at its origin; however, it was partially visualized in a retrograde manner due to blood flow from the posterior circulation via the persistent trigeminal artery (D; black arrow, E; white arrow).

3D: three-dimensional; DA: digital angiography; DSA: digital subtraction angiography; PTA: percutaneous transluminal angioplasty

Discussion

The efficacy of FD treatment in fetal-type PComA aneurysms remains a subject of ongoing debate. Numerous studies have reported significantly lower occlusion rates in aneurysms associated with fetal-type PComA compared to non-fetal-type cases. A recent meta-analysis demonstrated a complete occlusion rate of approximately 42% in fetal-type cases, markedly lower than the 77% observed in non-fetal-type aneurysms.⁴⁾

Early small-scale reports even documented zero occlusion following FD treatment in fetal-type PComA aneurysms.⁶⁾ More recent aggregated data suggest that the average occlusion rate in these cases remains around 30%.⁶⁾ However, some improvement has been noted with extended follow-up and technical modifications; for instance, a recent study reported an occlusion rate of approximately 75% in fetal-type cases.⁶⁾

Despite these advances, fetal-type PComA aneurysms are still widely considered refractory to FD monotherapy. This resistance is thought to be primarily due to unfavorable hemodynamic conditions. In fetal-type configurations, the PCA receives substantial antegrade flow via a dominant PComA, which may divert blood away from the aneurysm sac even after FD deployment. As a result, intra-aneurysmal flow reduction may be insufficient to promote thrombosis and complete occlusion. Given these challenges, fetal-type PComA aneurysms continue to represent a complex subset within the expanding indications for FD treatment, and further investigation is warranted to optimize therapeutic strategies.

Management strategies for FD treatment in fetal-type PComA aneurysms

As previously discussed, fetal-type PComA aneurysms present significant therapeutic challenges and carry a heightened risk of complications. In clinical practice, various technical modifications and alternative strategies have been considered to improve outcomes and mitigate risks associated with FD treatment in this anatomically and hemodynamically complex subset. Several adjunctive techniques have been explored to enhance the efficacy of FD therapy in treatment-resistant aneurysms, including fetal-type PComA aneurysms.

Overlapping flow diverter

Computational fluid dynamics studies have demonstrated that overlapping multiple FDs can significantly reduce intra-aneurysmal flow velocity and promote thrombosis.^8,9) Clinically, overlapping FD has been associated with improved complete occlusion rates and more rapid aneurysm healing.¹⁰⁾ However, this approach may also increase the risk of ischemic complications, necessitating careful patient selection and perioperative management.¹⁵⁾

Flow diverter with coils

Combining FD placement with adjunctive coiling has shown promise in improving complete occlusion rates, as reported in multiple meta-analyses.^11,12) Interestingly, dense coil packing is not required; even a modest packing density of approximately 15% has been associated with enhanced occlusion outcomes.¹⁶⁾ Given its efficacy, coil-assisted FD therapy is increasingly recommended for aneurysms refractory to FD monotherapy, particularly large aneurysms ≥10 mm and those involving branch vessels.¹⁷⁾

Overlapping FD with coiling

Considering the outcomes of OFD and FDC, treatment with OFDC appears to be the most effective approach for promoting intra-aneurysmal thrombosis.

In our series, Case 3, which involved concomitant aneurysms incorporating the PComA and the anterior choroidal artery, OFDC was performed for the PComA aneurysm, and OFD only was performed for the anterior choroidal artery aneurysm. As a result, the PComA aneurysm achieved complete occlusion, whereas the anterior choroidal artery aneurysm did not. These findings suggest that, in the presence of branch vessels arising from the aneurysm, adjunctive coiling in addition to OFD placement may promote a more robust thrombotic effect. Overlapping an additional FD after recurrence is an option when initial FD treatment (with or without coils) fails to achieve complete occlusion. This approach does not increase ischemic complication rates; however, cure rates remain modest, particularly in aneurysms with incorporated branch vessels.¹⁸⁾ Our approach was to employ aggressive treatment upfront to achieve high cure rates despite the presence of branch vessels arising from the aneurysm, while utilizing triple therapy to minimize ischemic complications.

Strategies for perioperative ischemic complications

OFDC is considered one of the most potent thrombosis-promoting strategies in cerebral aneurysm therapy. However, its aggressive flow-reducing effect may increase the risk of ischemic complications in branch vessels, such as the PComA and perforators, due to rapid intra-aneurysmal thrombosis. Maintaining patency of PComA originating from aneurysms requires gradual thrombosis within the aneurysm sac, necessitating methods to control post-procedural thrombosis progression.¹⁹⁾ We implemented perioperative anticoagulation therapy using DOACs in addition to standard DAPT.²⁰⁾ Given reports that DOACs may reduce aneurysm healing rates following FD treatment,¹³⁾ we administered reduced doses compared to standard atrial fibrillation protocols. In addition, we limited the duration to the first 4 weeks postoperatively, when thrombotic complications are most likely.²¹⁾ Prolonged triple therapy has been associated with increased hemorrhagic risk,²²⁾ so short-term administration was adopted.²³⁾ This regimen-short-term, low-dose DOAC in combination with DAPT-may reduce perioperative ischemic complications without significantly increasing hemorrhagic risk.

Hemodynamic considerations and vascular remodeling of PComA and PCA

In cases with well-developed P1 segments of the PCA, occlusion of the PComA following FD placement does not compromise posterior circulation, allowing for complete aneurysm occlusion via PComA remodeling. Subanalysis of the SCENT (Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide-Neck Aneurysms) trial revealed that PComA occlusion occurred in approximately half of treated cases without clinical sequelae.

However, fetal-type PComA aneurysms pose a unique challenge. In these cases, the PComA arises directly from the aneurysm sac, and the P1 segment is often hypoplastic. FD treatment in this configuration is associated with low complete occlusion rates^4,6) and a heightened risk of ischemic complications due to compromised posterior circulation.

OFDC applications in fetal-type cases can effectively reduce flow to both the aneurysm and the PComA. Concurrent anticoagulation therapy provides a temporal buffer for vascular remodeling. Ideally, therapeutic success requires a reduction in PComA diameter and compensatory enlargement of the PCA P1 segment.²⁴⁾ In our series, all fetal-type PComA cases demonstrated PComA narrowing or occlusion accompanied by P1 segment expansion, supporting the feasibility of this remodeling-based strategy.

This treatment approach requires careful patient selection, meticulous technique, and close monitoring due to its potent thrombotic effects. OFDC should not be applied to all fetal-type PComA aneurysms but should be reserved for cases refractory to FD monotherapy, particularly those in which the PComA arises from the aneurysm body and the P1 segment is hypoplastic. Cases in which the PComA originates from the aneurysm neck or the P1 segment, which are relatively robust, are more likely to be cured without such aggressive treatment as OFDC. When the P1 segment shows no anterograde flow on angiography, PComA occlusion carries a high risk of tuberothalamic infarction.²⁵⁾ Preservation of the PComA is essential in such fetal-type cases with P1 hypoplasia, and our triple therapy strategy may be useful to prevent acute occlusion.

The limitation of this study is that the maximum aneurysm size in this cohort was 12 mm, and therefore, the efficacy for larger aneurysms is uncertain. Further prospective studies with larger patient cohorts are needed to establish optimal antiplatelet and anticoagulation protocols and to validate the long-term safety and efficacy of this treatment strategy.

Conflicts of Interest Disclosure

All authors have no conflict of interest.

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