Endovascular treatment of aneurysm remnants with the Contour Neurovascular System after previous treatment

Abstract

Objective

The Contour Neurovascular System (CNS) is a novel intrasaccular flow disrupting device with a semi-3D cup-like shape for the treatment of intracranial aneurysms. This study investigates the potential and limitations of the CNS for embolization of aneurysm remnants after previous treatment.

Methods

Ten cases of aneurysm recurrence treatment with the CNS were analyzed from a single-center database. Technical success, procedural aspects, complications, and angiographic results were evaluated.

Results

The aneurysms (median width: 5.3 mm, median neck width: 3.8 mm) were located in the anterior communicating artery (4), basilar tip (3), internal carotid artery (1), middle cerebral artery (1), and superior cerebellar artery (1). The aneurysms were initially treated endovascularly (9) and by clipping (1). Retreatment failed in one case where the smallest available CNS proved to be too small and had to be removed. Adjunctive coiling was performed in two large remnants of partially thrombosed basilar tip aneurysms. There were no procedural complications or morbidity. At a median follow-up of nine months, 4/8 (50%) aneurysms were completely occluded, 2/8 (25%) had neck remnants, and 2/8 (25%) had aneurysm remnants. The two aneurysm remnants were retreated with coiling and stent-assisted coiling, respectively.

Conclusions

CNS treatment of aneurysm remnants may be feasible, especially for shallow, wide-necked aneurysm geometries. Further studies are needed to identify aneurysm subsets that benefit from CNS retreatment and to define mid- and long-term occlusion rates.

Introduction

Over the past decade, intrasaccular flow disruption has become a well-established concept for the treatment of intracranial aneurysms, particularly wide-neck and bifurcation aneurysms, which are difficult to treat with conventional endovascular means.^1–4 In addition to the Woven Endobridge (WEB; Sequent Medical, Aliso Viejo, CA, USA), available for more than a decade now, the Contour Neurovascular System (CNS; Cerus Endovascular, Fremont, CA, USA) has recently been introduced.^5,6 The CNS is a densely woven, dual-layer, cup-shaped device that reconstructs the aneurysm neck and covers the lower half of the aneurysm. Early studies indicate a reasonable safety and efficacy profile for this device.^5,7,8

Aneurysm recurrence is a major concern with endovascular coiling with reported recurrence rates of up to 30%.^9,10 Reconstructive techniques such as stent-assisted coiling have a lower but still relevant recanalization rate of 5–20%, but at the cost of a potentially increased procedural risk and the need for antiplatelet medication.^11–14

While there are some reports on the treatment of aneurysm recurrence with the WEB, there are very few data on the treatment of recurrent aneurysms with the CNS.^15,16 Our series describes a monocentric institutional experience in treating aneurysm remnants with the CNS, particularly those with a wide-neck geometry, focusing on feasibility, complications, and angiographic results.

Methods

Consecutive patients treated with the CNS for intracranial aneurysms at a single institution between October 2018 and January 2023 were retrospectively reviewed to identify cases in which the CNS was used to treat residual and recurrent aneurysms. The study was approved by the Ethical Committee of the medical faculty at the Ludwig-Maximilians-University Munich (No. 23-0017). Additional informed consent was not required due to the retrospective study design.

The CNS

The CNS is a dual-layer half sphere made of densely woven drawn filled tube wires that connect to a proximal platinum marker. This marker is linked to the introducer wire for detachment. The entire shape of the CNS and its proximal marker are visible under fluoroscopy. The device comes in sizes of 5, 7, 9, 11, and 14 mm and it should be large enough to cover the neck and to make contact with the aneurysm wall to ensure stable positioning. The appropriate diameter is chosen based on the neck width and equatorial dome width of the aneurysm. While 5, 7, and 9 mm devices can be deployed through a 0.021″ microcatheter, the 11 and 14 mm need a 0.027″ microcatheter. Once deployed, the CNS—originally a flat disc-like shape—is transferred to its desired semi-2D shape that conforms to the lower half of the aneurysm, sealing the neck and reducing inflow into the aneurysm. The delivery system allows retrieval and repositioning before electrolytic detachment.

Procedure and antiplatelet therapy

All procedures were performed under general anesthesia via a transfemoral approach, under a bolus of 5000 units of heparin. If additional coiling was needed, it was performed via a separate jailed microcatheter as described previously. ¹⁷ Antiplatelet therapy was started 5–7 days before treatment to allow for additional bail-out stenting and consisted of either acetylsalicylic acid (ASA) as monotherapy or dual antiplatelet therapy with ASA and clopidogrel or ASA and ticagrelor. No stents were needed in our series and while clopidogrel and ticagrelor were stopped immediately, ASA was continued for eight weeks.

Data collection and angiographic evaluation

Data were obtained by chart review and included patient demographics, initial target aneurysm rupture status, previous target aneurysm treatment, CNS size, use of additional implants, procedural complications (including clinically relevant and technical complications), and potential retreatments. Procedural morbidity was defined as a one-point increase on the modified Rankin Scale (mRS) at discharge compared to baseline.

Conventional four-vessel digital subtraction angiography was used to determine the location of the aneurysm and to measure the width, height, and neck width of the aneurysm remnant. Aneurysm occlusion was categorized as complete occlusion, neck remnant, or aneurysm remnant, with complete occlusion and neck remnant combined as adequate occlusion.

Statistical analysis

Descriptive statistics were used, with categorical variables presented as numbers and percentages, and continuous variables presented as medians with range.

Results

Patient and aneurysm characteristics

Of the 76 patients treated with the CNS during the study period, the device was used for recurrent aneurysms in 10 patients. The median patient age was 53 years (range: 30–73 years) and six patients were female. Individual aneurysm characteristics are shown in Table 1.

Table 1.

Individual aneurysm characteristics.

Case	Aneurysm location	Initial rupture status	Initial treatment	Width (mm)	Height (mm)	Neck width (mm)
1	BA tip	R	SAC	6.9	18.0	5.7
2	Paraophthalmic ICA	UR	WEB	5.7	3.6	3.6
3	Acom	R	Coiling	1.8	2.0	1.6
4	MCA bifurcation	UR	WEB	4.0	5.0	4.8
5	Acom	R	Coiling	3.3	2.0	2.5
6	BA tip	R	SAC	9.2	12.2	6.3
7	BA tip	UR	WEB	5.6	3.1	5.8
8	SUCA	R	Coiling	2.6	3.3	2.4
9	Acom	R	Clipping	10.4	9.8	4.0
10	Acom	R	Coiling	2.4	2.6	2.0

BA: basilar artery; ICA: internal carotid artery; Acom: anterior communicating artery: MCA: middle cerebral artery; SUCA: superior cerebellar artery; R: ruptured; UR: unruptured; SAC: stent-assisted coiling; WEB: Woven Endobridge.

Four aneurysms were located at the anterior communicating artery (Acom), three at the basilar artery (BA) tip, and one each at the paraophthalmic internal carotid artery, middle cerebral artery bifurcation, and superior cerebellar artery. Four aneurysms were pretreated with coiling, three with WEB, two with SAC, and one with clipping.

The median residual aneurysm width was 5.3 mm (range: 1.8–10.4 mm) and the median residual aneurysm height was 3.5 mm (range: 2.0–18.0 mm). The median neck width was 3.8 mm (range: 1.6–6.3 mm). All aneurysm remnants were considered as wide necked.

Procedural aspects

Aneurysm treatment with the CNS was successful in nine aneurysms using different CNS sizes ranging from 5–11 mm. The most frequently used device size was the CNS 5 mm (five cases), followed by the CNS 11 mm (three cases) and the CNS 7 mm (two cases). Additional coils were used in three cases to maximize aneurysm occlusion. In the two aneurysms with a previously implanted stent (cases 1 and 6), probing of the aneurysm remnant through the stent pores was unproblematic and the stent did not interfere with proper device deployment and positioning. In case 10, CNS implantation failed in an Acom aneurysm previously treated with coiling. The 5 mm CNS used proved to be too large as the device protruded too far into the parent artery. The CNS was removed and the aneurysm was treated with a WEB SL 3 × 2 mm instead. No additional balloons or stents were used to stabilize the device position. There were no procedural complications and no treatment-related morbidity. Procedural characteristics are detailed in Table 2. Figures 1 and 2 illustrate the cases 5 and 9 with successful CNS implantation.

Table 2.

Procedural aspects and angiographic outcome.

Case	CNS size (mm)	Adjunctive material	Microcatheter size	Follow-up period (months)	Aneurysm occlusion	Retreatment
1	11	Coils	0.027″	6	AR	CNS 11 mm and coils
2	5		0.027″	24	NR	No
3	5		0.021″	31	CO	No
4	7		0.021″	7	NR	No
5	5		0.021″	5	CO	No
6	11	Coils	0.027″	15	AR	Coiling
7	7		0.021″	28	CO	No
8	5		0.021″	11	CO	No
9	11	Coils	0.027″	n.a.	n.a.	n.a.
10	5		0.021″	– a	– a	– a

CO: complete occlusion; NR: neck remnant; AR: aneurysm remnant; n.a.: not available.

^aAngiographic follow-up not shown, as CNS implantation failed.

Figure 1.

Case 5. (a and b) Digital subtraction angiography (DSA) images show aneurysm recurrence (neck size: 2.5 mm, mean dome width: 3.25 mm, height: 2 mm) after coiling of an initially ruptured aneurysm of the anterior communicating artery (white arrows). (c) Road map shows the probing of the recurrent aneurysm sac. (d) Road map shows the unfolded CNS inside the microcatheter (Phenom 21, black arrow). (e) Initially, a 7 mm CNS is inserted, but is found to be too large and does not fully deploy. This is easily removed by pulling it back into the microcatheter. (f) Insertion of a fully deployed 5 mm CNS and electrolytic detachment after verifying correct position and maintaining perfusion of the downstream arteries. (g) Arterial phase of the final DSA control shows residual inflow into the recurrent aneurysm sac immediately after CNS implantation. (h) Residual contrast in the aneurysm sac persists into the venous phase, demonstrating the stasis that has already occurred in the aneurysm sac.

DSA: digital subtraction angiography.

Figure 2.

Case 9. (a) Magnetic resonance angiography (MRA) shows recurrence (neck size: 4.0 mm, mean dome width: 10.4 mm, height: 9.8 mm) of an initially ruptured aneurysm of the anterior communicating artery treated by clipping approximately 20 years ago. (b and c) Computed tomography angiography (CTA) and volumetric 3D reconstruction from rotational angiography confirm the finding of aneurysm recurrence and show the inserted aneurysm clip (white arrow in B). (d and e) The aneurysm recurrence shown in two planes on digital subtraction angiography (DSA). (f and g) Initially, a 14 mm CNS was placed in the recurrent aneurysm sac, which proved to be slightly too large on 3D flat-panel CT and was removed. (h) Insertion of a 11 mm CNS with jailing of a microcatheter (tip marked with black arrow) for subsequent coiling. (i) Recurrent aneurysm sac filled with several coils, some of which were overlong. The CNS acts as a neck bridging device and secures the position of the coils despite the wide aneurysm neck. (j) The final DSA scan shows successful elimination of the aneurysm recurrence from the circulation with preserved perfusion of all downstream vessels, including both A2 segments. The absence of the A1 segment on the right side is congenital. (k) Venous phase of the final DSA scan shows persistent contrast in the neck area overlapping the CNS, indicating that stasis has already occurred.

DSA: digital subtraction angiography.

Angiographic outcome

The patient with failed CNS implantation was excluded from the angiographic outcome analysis. Angiographic control was available for eight patients with a median follow-up of nine months (range: 5–31 months). At the last follow-up, four (50.0%) aneurysm was completely occluded, two (25.0%) had a residual neck, and two (25.0%) had a large aneurysm remnant.

Both cases with residual aneurysm were located at the basilar tip and were previously treated with SAC. Both cases also had the largest aneurysm remnants in this series prior to CNS embolization (Case 1: 18.0 mm, Case 6: 12.2 mm) and were therefore treated with adjunctive coils. In both cases, recanalization occurred due to coil compaction and migration of the CNS within the aneurysm. The first case was retreated with a CNS of the same size and additional coils, achieving subtotal occlusion at further follow-up. The second case was retreated with coils only, achieving immediate complete occlusion.

Discussion

Aneurysm remnants have a relevant risk of spontaneous rupture or rerupture. ¹⁸ Due to the devastating and potentially life-threatening nature of subarachnoid hemorrhage, it is important to individually assess the risk of aneurysm hemorrhage or rebleeding versus the risks associated with retreatment. ¹⁹ To date, the majority of aneurysm remnants is still treated with conventional coiling, that has low complication rates but is not feasible for all aneurysm geometries. ²⁰

While the WEB occludes the aneurysm dome by volumetric displacement, the CNS mainly adapts to the neck in a semi-2D fashion and without occupying volume itself.^5,21,22 This feature may be advantageous for the shallow, wide-necked geometry often seen in aneurysm recurrences and remnants. ²³ Unlike WEB, which requires a saccular aneurysm shape similar to the device itself, CNS can be used on a wider variety of aneurysm geometries and on aneurysms/aneurysm remnants that are too large for WEB treatment. In this context, additional coil embolization of the aneurysm sac by deploying the coils through a jailed microcatheter is possible after CNS implantation, with the CNS acting as a stent plug to prevent coil protrusion into the parent artery. ¹⁷ In our experience, the CNS can usually be used as a stand-alone technique for aneurysm retreatment, with additional coiling considered for large remnants and intraluminal stents used as a bail-out option to further stabilize the CNS position, for example, if it protrudes into the parent vessel.

In the present series of 10 aneurysms, only one aneurysm proved too small for the CNS and the device had to be removed. With the introduction of smaller CNS sizes, small remnants may become amenable in the future. Additional coils were used in the three largest aneurysm remnants. The rationale of additional coiling was to counteract a potential displacement of the CNS into the aneurysm sac in large remnants or in previously ruptured aneurysms to increase thrombogenicity and shorten the time until the dome was permanently occluded, since to date, the evidence for CNS in ruptured aneurysms—acute and subacute—is scarce.

There are few reports of WEB treatment of residual aneurysms after initial coiling, WEB embolization, or clipping. WEB implantation was feasible in 16/17 (94%) in the study by Gawlitza et al., 17/17 (100%) in the study by van Rooij et al., and 10/11 (89%) in the study by Goertz et al.^15,16 The authors collectively concluded that the WEB may constitute a safe and efficient treatment option for aneurysm remnants with unfavorable anatomical configuration for conventional coiling, especially wide-necked bifurcation aneurysms. ¹⁵

The concept of flow diversion and flow disruption involves promoting progressive aneurysm occlusion over time. ²⁴ Therefore, it is not realistic to expect high rates of complete occlusion in the early and mid-term. In this series, the CNS treatment achieved complete and adequate occlusion in 43% and 71%, respectively. Due to the small number of patients followed, these results cannot be generalized. However, the angiographic results of the CNS studies in unselected aneurysm groups tend to be higher, for example, 44% and 80% in the study by Liebig et al. and 75% and 88% in the study by Hecker et al.^5,25

The cited studies of WEB for recurrent aneurysms reported comparably lower occlusion rates than the present study, with complete and adequate occlusion achieved in 33% and 73% by Gawlitza et al., 29% and 64% by van Rooij et al., and 33% and 78% by Goertz et al.^15,16,26

In our series, both aneurysms that recanalized after CNS retreatment were initially partially thrombosed, large basilar tip aneurysms. To counteract migration of the CNS, the large remnants were additionally treated with coils to fill the aneurysm sac. However, follow-up showed repeated coil compaction beyond the CNS and subsequent migration of the CNS into the aneurysm dome.

In general, partially thrombosed aneurysms are difficult to treat both surgically and endovascularly and present a particular challenge for neurointerventionalists. Previous studies have suggested that partially thrombosed aneurysms may not be well suited for intrasaccular flow disruption, as they are associated with comparatively high recurrence rates.^27,28

Potential alternative treatment options for wide-necked aneurysm remnants include stent-assisted coiling and microsurgical clipping. Stent-assisted coiling, though often feasible, mandates long-term antiplatelet therapy and has shown higher complication rates than simple recoiling. ²⁹ Tähtinen et al. reported a major complication rate of 11% and an unfavorable outcome of 9% in a series of SAC for retreatment. ³⁰ Microsurgical clipping is known to be a highly effective treatment option for intracranial aneurysms, including recurrent aneurysms. ³¹ Daou et al. reported an immediate occlusion rate of 97.3% and a recurrence rate of 1.8% for clipped aneurysm remnants, which is superior to endovascular techniques. However, the morbidity rate of 10% was not negligible ³² and the previously placed implants—for example, a large coil mass—may prevent effective or safe positioning of a clip across the neck.

In terms of procedural safety, there were no procedural complications and no treatment-related morbidity, despite the fact that all aneurysm remnants were wide-necked, a potential risk factor for thromboembolic events. ³³

In general, early evidence suggests that treatment with the CNS is safe. The literature reports a disabling stroke rate of 5.9% in the study by Liebig et al., a minor stroke rate of 1.7% with no major strokes in the study by Biondi et al., and a major stroke rate of 2.5% in the study by Hecker et al.^5,7,25

Ultimately, the choice of retreatment modality is a multidisciplinary task. The results of the present study indicate that the CNS appears to be safe and feasible for aneurysm remnants, allowing this device to be used at least in complex geometries when other endovascular methods are not feasible. Appropriate aneurysm selection and mid- and long-term angiographic results need to be addressed in future studies.

Limitations

The limitations of this study are mainly related to its retrospective design and the limited number of patients included. In particular, the lack of angiographic follow-up in half of the patients limits the generalizability of the results. In addition, varying aneurysm characteristics and multimodal treatment with CNS and coils may potentially bias clinical and angiographic results.

Conclusions

The results of the current study indicate that treatment of wide-necked aneurysm remnants and recurrences is feasible, while there were no procedural complications or treatment-related morbidity. In two large aneurysm remnants of initially partially thrombosed basilar artery tip aneurysms, coil compaction and subsequent CNS migration required retreatment. Further studies are needed to identify aneurysm subsets that benefit from CNS treatment and to define mid- and long-term occlusion rates.