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Original research
Stent-assisted coil embolization of aneurysms with small parent vessels: safety and efficacy analysis
  1. Anna Luisa Kühn,
  2. Samuel Y Hou,
  3. Ajit S Puri,
  4. Christine F Silva,
  5. Matthew J Gounis,
  6. Ajay K Wakhloo
  1. Division Neuroimaging and Intervention and New England Center for Stroke Research, Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
  1. Correspondence to Dr Ajay K Wakhloo, Division Neuroimaging and Intervention, Department of Radiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA; ajay.wakhloo{at}


Background Stent-assisted coil embolization (SACE) is a viable therapeutic approach for wide-neck intracranial aneurysms. However, it can be technically challenging in small cerebral vessels (≤2 mm).

Objective To present our experience with stents approved for SACE in aneurysms with small parent arteries.

Methods All patients who underwent stent-assisted aneurysm treatment with either a Neuroform or an Enterprise stent device at our institution between June 2006 and October 2012 were identified. Additionally, we evaluated each patient's vascular risk factors, aneurysm characteristics (ruptured vs non-ruptured, incidental finding, recanalized) and follow-up angiography data.

Results A total of 41 patients with 44 aneurysms met our criteria, including 31 women and 10 men. Most of the aneurysms were located in the anterior circulation (75%). Stent placement in vessels 1.2–2 mm in diameter was successful in 93.2%. Thromboembolic complications occurred in 6 cases and vessel straightening was seen in 1 case only. Initial nearly complete to complete aneurysm obliteration was achieved in 88.6%. Six-month follow-up angiography showed coil compaction in three cases, one asymptomatic in-stent stenosis and stent occlusion. Twelve to 20-months’ follow-up showed stable coil compaction in two patients compared with previous follow-up, and aneurysm recanalization in two patients. Twenty-four to 36-months’ follow-up showed further coil compaction in one of these patients and aneurysm recanalization in a previous case of stable coil compaction on mid-term follow-up.

Conclusions Our results suggest that SACE of aneurysms with small parent vessels is feasible in selected cases and shows good long-term patency rates of parent arteries.

  • Aneurysm
  • Stent
  • Coil

Statistics from


The implementation of stent devices in the neurovascular field as a treatment option for intracranial aneurysms has enabled interventionalists to treat many of those aneurysms that had been previously thought to be untreatable owing to their morphology, including those with unfavorable dome to neck ratios and/or location within the circle of Willis.1

Since the publication of the results of the International Subarachnoid Aneurysm Trial in 2002,2 aneurysm treatment has gravitated towards endovascular treatment. However, some aneurysms with unfavorable anatomy/dome to neck ratio are not solely suitable for simple coil embolization. Other adjuvant techniques like balloon-assisted coil embolization have been, and are being, used for some of these aneurysms.

Stent-assisted coil embolization (SACE) offered a viable approach for treatment of wide-neck intracranial aneurysms (neck width ≥4 mm). This remains a technically challenging procedure in small cerebral vessels and only a limited number of case series on treatment of wide-neck aneurysms in such vessels is available.1 ,3–5 Only two stents are approved for SACE in the USA.

The Enterprise vascular reconstruction device (Codman, Miami Lakes, Florida, USA) is a self-expandable, highly flexible stent that is made of nitinol and possesses a closed-cell design. The Neuroform stent (Stryker Neurovascular, Fremont, California, USA) is also a self-expandable stent manufactured from nitinol but possesses a semi-open-cell structure. Both stent devices can be delivered through standard microcatheters and are used for stent-assisted coiling procedures.

The instructions for use of the devices document suggest their application for treatment of wide-neck intracranial aneurysms that arise from intracranial arteries with a diameter of ≥3.0 and ≤4 mm (Enterprise) and ≥2.0 and ≤4.5 mm (Neuroform).

Several distal intracranial vessels have an arterial diameter of around 2.0 mm or even smaller; the use of the stent devices in these vessels is off-label. Stent deployment in vessels of diameters not included in the instructions for use is still debatable.6 ,7

We report our experience with both, the semi-open-cell (Neuroform) and the closed-cell (Enterprise) stent examining device safety, deployment feasibility and treatment effectiveness in wide-neck aneurysms with parent vessels measuring ≤2.0 mm in diameter.

Materials and methods

This retrospective study was approved by our hospital institutional review board.

Patients and aneurysms

All patients who underwent stent-assisted aneurysm treatment with either a Neuroform or an Enterprise stent device at our institution between June 2006 and October 2012 were identified. We then measured the diameter of the parent vessel and included all patients with a parent artery diameter of ≤2 mm. Patients’ vascular risk factors, aneurysm characteristics (ruptured vs non-ruptured, incidental finding, recanalized) and follow-up angiography data were evaluated.

Partial data of this subgroup analysis were previously published.8

Endovascular treatment

All SACE interventions were performed under general anesthesia. Digital subtraction angiography was performed on a state-of-the-art biplane angiography system (Allura Biplane FD20/20, Philips Healthcare, Best, The Netherlands). Heparin was infused during the endovascular intervention to achieve an activated clotting time of 2–2.5 times that of the patient's baseline in all cases. Patients were premedicated with 325 mg of aspirin and 75 mg of clopidogrel except for one case in which the aneurysm was ruptured.



A total of 41 patients with 44 aneurysms met our criteria, including 31 female (75.6%) and 10 male (24.4%). Their mean age was 54.5 years (range 25–80 years). Patient risk factors included hypertension (61.0%), smoking (34.1%), dyslipidemia (26.8%), coronary artery disease (14.6%) and diabetes (9.8%). In 26.8% the patients’ past medical history was non-contributory (table 1).

Table 1

Patient demographics and aneurysm characteristics

Most of the aneurysms were located in the anterior circulation (75%) with 14 anterior communicating artery aneurysms (34.1%) and 13 middle cerebral artery aneurysms (29.5%). Other aneurysm locations included basilar tip (n=6), posterior cerebral artery (n=3), pericallosal artery (n=3), anterior cerebral artery (n=2), posterior inferior cerebellar artery (PICA; n=1) and the superior cerebellar artery (SCA; n=1). Mean parent artery diameter was 1.7 mm (range 1.2–2 mm).

Aneurysms were detected as incidental findings in 34.1% of cases. Symptoms related to the aneurysm were seen in 31.8%. Fourteen aneurysms had been previously coiled, but recanalized, and were thus re-treated with SACE. One aneurysm was ruptured. In 54.5% of cases (n=24) a Neuroform stent (figure 1) was used; the remaining cases were treated with an Enterprise stent (figure 2). The Neuroform and Enterprise stents were used to treat anterior circulation aneurysms in 18 and 15 cases, respectively. Aneurysms in the posterior circulation were treated with a Neuroform stent in six cases and with an Enterprise stent in five. Stent placement was successful in 41/44 interventions. Stent misplacement was due to technical difficulties in two cases resulting in partial and no aneurysm neck coverage. Both cases, however, showed complete aneurysm obliteration during the follow-up time available in these two patients (patient No 1=6 months, patient No 6=3 years). One stent migration was seen that resulted in partial aneurysm neck coverage with still sufficient support of the intra-saccular coil mass and no occlusion of any collateral branches. Follow-up angiography at 6 months showed complete aneurysm obliteration. No further follow-up was available.

Figure 1

(A) Digital subtraction angiography shows a wide-necked left posterior inferior cerebral artery aneurysm. (B) Placement of a Neuroform 4 mm×20 mm stent was from the vertebral artery (white arrow) to the posterior inferior cerebral artery aneurysm (black arrow). (C) The wide-necked aneurysm was successfully coiled with stent-assisted coil embolization. The Neuroform stent lies within the vertebral artery (white arrow) and the posterior inferior cerebral artery aneurysm (black arrow). (D) 3-year follow-up angiography shows a patent stent without aneurysm recanalization.

Figure 2

(A) Digital subtraction angiography shows a recanalized pericallosal–callosomarginal aneurysm. (B) An Enterprise 4.5 mm×14 mm stent was placed with its distal end in the proximal right callosomarginal artery and the proximal end within the A2 segment of the right anterior cerebral artery. (C and D) Follow-up angiography at 6 and 18 months shows no in-stent stenosis and complete aneurysm obliteration.

Periprocedural complications

Stent misplacement occurred in threes cases, one of which required the placement of a second stent (table 2).

Table 2

Treatment and outcome

Periprocedural thromboembolic complications occurred in six interventions (13.6%; three cases each for Neuroform and Enterprise) but were immediately treated with intra-arterial thrombolysis. Complete thrombolysis of the clot was achieved in five cases. In one patient clot fragments migrated distally and final angiography showed flow stagnation within distal cortical branches of the ipsilateral posterior cerebral artery. Nevertheless, this patient did not show any neurologic deficits upon awakening.

Aneurysm rupture during coiling and vessel straightening was seen in one case (2.3%) each.

Postprocedural outcome

Immediate control angiography after the intervention showed nearly complete to complete aneurysm obliteration in 39 aneurysms (88.6%). In two cases, there was only minor residual filling of the aneurysm neck.

Angiographic and clinical outcome at 6 months

Six-month follow-up digital subtraction angiography was available for 33 patients (80.5%). Coil compaction was seen in three cases, one of which also showed asymptomatic in-stent stenosis (2.3%) but no re-treatment was necessary. One asymptomatic stent occlusion was seen which did not require intervention owing to good collateral flow to the affected brain region.

Angiographic and clinical outcome at 12–20 months

Follow-up angiography at 12–20 months was performed in 27 patients (65.9%). In two cases coil compaction remained stable compared with the 6-month follow-up results. In two cases new aneurysm recanalization was seen. No in-stent stenosis was found.

Angiographic and clinical outcome at 24–36 months

Follow-up results at 24–36 months were available for 14 patients (34.1%).

In one patient coil compaction remained stable compared with the 15 months’ follow-up. Further coil compaction was seen in one patient who had previously had recanalization at the 6-month follow-up and stable coil compaction at the 12-month follow-up, and in another patient who had shown recanalization at the 12-month follow-up angiography. Re-treatment was only necessary in these two cases.

Unfortunately, the patient showing coil compaction at the 6-month follow-up with stable findings at the 12-month follow-up angiography did not undergo a 24–26-month follow-up examination.


The instructions for use for both Food and Drug Administration Humanitarian Device Exemption approved stents, Neuroform and Enterprise, for the use in SACE of wide-neck aneurysms is in vessels ≥ 2 and ≥3 mm in luminal diameter, respectively. From our single-center experience, we report placement of intracranial stents in small vessels between 1.2 and 2.0 mm in luminal diameter. In our experience, SACE in small vessels is a safe and effective means for treatment of selected wide-neck aneurysms amenable to this endovascular approach.

Of the 41 cases that were treated with SACE in small vessels, 39 cases showed nearly complete to complete aneurysm obliteration. Only two aneurysms demonstrated residual filling at the neck on follow- up angiography examinations. Only two cases required re-treatment of the aneurysm. This compares favorably with the reported literature of recanalization rates for coil embolization alone of up to 40% in a meta-analysis of the literature.9 SACE has been shown to allow for denser packing on the aneurysm since the stents can provide a scaffold at the aneurysm neck, enabling endothelial growth and flow modification, and thus permitting better aneurysm healing.

Despite these results, caution needs to be taken when choosing the size of the stent as oversizing may enlarge the stent cells to sizes larger than the neck of the aneurysm.

Periprocedural thromboembolic complications occurred in six patients. Complete clot lysis was immediately achieved in four cases. There was also one intraprocedural aneurysm rupture during coiling. No neurologic deficits were seen after the procedure.

Others have suggested increased complication rates for closed-cell design stents as compared with semi-open-cell design stents due to vessel wall apposition.10 However, we found no difference in the complication rates between the two devices used in our study. The use of either the Enterprise or Neuroform stent was at the discretion of the treating neurointerventionalist and the decision was made on a case-by-case basis.

Vessel straightening was seen with placement of an Enterprise stent in a pericallosal artery aneurysm. In our experience, the closed-cell design stent has a greater tendency to slightly alter normal vascular anatomy owing to its design. However, vascular remodeling back to baseline anatomy typically occurs over time, as was seen in our case.

There are technical differences in the delivery between the Enterprise and Neuroform stents. Delivery of the open-cell design Neuroform stent to more distal vessels may be more difficult as it requires the use of a 0.027" diameter microcatheter rather than the 0.021" diameter microcatheter used to deliver the closed-cell design Enterprise stent. The larger size of the microcatheter is less advantageous in navigating more tortuous and distal vessels. Nevertheless, it is important to keep in mind that navigation of either microcatheter occurs in very small vessels and this circumstance itself already demands a certain level of experience and expertise.


Despite the overall promising results of our analysis, the off-label implementation of the Neuroform or Enterprise stent in parent vessels ≤2.0 mm in diameter should be performed only in selected cases. Intraprocedural thromboembolic events represent an important complication during stent placement in small parent arteries.

Future technologic advances in stent design and delivery through 0.017" microcatheters (or smaller) will hopefully allow for safe delivery of devices in more tortuous and distal vessels.



  • Contributors Study design: AKW. Data collection: ALK, SYH, CFS. Interpretation of data: ALK, SHY, ASP, AKW. Literature research: ALK, CFS, MJG. Drafting first manuscript version: ALK, SYH, ASP. Revision of manuscript for important intellectual content: CFS, MJG, AKW. Approval of final manuscript: all authors.

  • Competing interests None declared.

  • Ethics approval Hospital institutional review board.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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