Indications of the two used stents included mainly complex unruptured or ruptured aneurysms, including fusiform, large and/or giant, dissecting or wide-neck aneurysms. In addition, small aneurysms, which may not be embolized by conventional coiling and recurrences, were considered amenable to stent-assisted coiling. EP stents were used for aneurysms arising from a parent vessel with a diameter of 2.5–4 mm, while ST stents were recommended for aneurysms arising from a parent vessel with a diameter of 2.5–5.5 mm. Wide-necked aneurysms were defined as having a neck of ≥4 mm or a dome-to-neck ratio of <2 mm.

The study was approved by the Institutional Review Board of the Zhujiang Hospital, Southern Medical University (Guangzhou, China). Written informed consent was obtained from the patients' families. In total, 81 patients with 90 aneurysms underwent treatment between January 2010 and January 2012. Initially, the aim was to use EP-assisted coiling in 43 aneurysms (47.8%) and ST-assisted coiling in 47 aneurysms (52.2%); however, EP-assisted coiling was not successful in four patients. These patients subsequently underwent treatment with the ST stent and all the aneurysms were successfully stented and coiled (EP, n=39, 43.3%; ST, n=51, 56.7%). The following information was recorded: Patient characteristics, aneurysm demographics, technical and procedure-related complications. Follow-up angiograms, typically obtained at six and 18 months, were reviewed for data on stent patency and aneurysm recurrence. Stent-related complications, including delayed stent migration and in-stent stenosis, were also recorded.

All the subjects with unruptured or non-acute ruptured aneurysms had been treated with dual antiplatelet therapy (75 mg clopidogrel and 100 mg aspirin per day) for five days prior to SAC. In the acute phase of the ruptured aneurysms, heparin was injected at the beginning and was maintained for 48 h. Four clopidogrel pills (300 mg) were crushed and injected into the nasogastric tube 2 h prior to surgery. The adequacy of the systemic anticoagulation therapy was monitored by frequent measurements of the activated clotting time (ACT). A baseline ACT was obtained prior to the bolus infusion of 5,000 IU heparin, and hourly thereafter. Clopidogrel (75 mg/day) was administered for six months post-surgery and daily administration of 100 mg aspirin was required for one year.

A biplane flat panel digital subtraction unit (Neurostar or Axiom Artis; Siemens Healthcare, Erlangen, Germany) was used to performed the endovascular procedure. After a 6-French sheath (Terumo, Fujinomiya, Japan) was successfully inserted into the right common femoral artery, the 6-F guide catheter (Envoy; Codman Neurovascular, Miami Lakes, FL, USA) was inserted into the parent vessel. Over a 0.014 inch Transend or Synchro microguidewire (Boston Scientific, Fremont, CA, USA), a microcatheter was delivered into the normal distal artery beyond the aneurysm by 1 to 2 cm. The aneurysm was then embolized once the coiling catheter was navigated within the aneurysm sac. Following the coiling procedure, the stent was pushed through the microcatheter and aligned directly across the neck of the aneurysm. When the appropriate position was achieved, the microcatheter was gently pulled back to unsheathe the stent. The stent would not be fully deployed until the distal markers were completely open. Typically, after full deployment, the position was confirmed by routine diagnostic cerebral angiography. Two stents could be inserted under a necessary position, while for an imperative reposition, repeating the aforementioned processes was required. Microplex coils (MicroVention, Inc., Aliso Viejo, CA, USA), GDCs (Boston Scientific) or Axium coils (ev3 Neurovascular) were delivered via the second catheter into the aneurysm, as reported previously (9). Following an ideal coiling embolization, the stent was detached from the push wire subsequent to routine diagnostic cerebral angiography using a high-resolution biplane angiographic unit.

Packing density, also known as the volume embolization ratio, was calculated as the ratio of the volume of the deployed coils to the aneurysm volume. The coil volume was calculated by summing the individual coil volumes, as indicated by the manufacturers. Aneurysm dimensions were measured by 3D images derived from rotational angiography. Subsequently, the aneurysm volume and packing density were calculated using Angiocalc software (available at http://www.angiocalc.com).

Angiographic follow-up examinations were performed with conventional angiography at six and 12 months post-surgery, and every year annually thereafter. For follow-up imaging, the patients underwent conventional digital subtraction angiography (DSA) or magnetic resonance angiography, or both. DSA was used for sole analysis whenever available. All the treated aneurysms were graded independently by two interventional neuroradiologists, using several views for each treated aneurysm, including 3D angiography. The angiographic results were classified according to the Raymond-Roy Occlusion Classification (10): Complete occlusion (class 1), neck remnant (class 2) and residual aneurysm (class 3).

Changes in the angiographic outcome were classified as follows: Stable (no change in coil configuration, obliteration grade or contrast filling), improved (progressive occlusion or involution of the neck remnant or contrast filling in the aneurysm) and recanalized (aneurysm recurrence evident due to neck growth, coil compaction, coil extrusion by aneurysm degradation or new sac formation). Additionally, newly visualized or increased contrast filling inside an aneurysm was regarded as recanalization.

Data were analyzed using the SPSS 13.0 statistical package (SPSS, Inc., Chicago, IL, USA), and are presented as the mean ± standard deviation. Statistical analyses were performed using the Student's t-test, Fisher's exact test, χ² test and analysis of variance, as appropriate, where P<0.05 was considered to indicate a statistically significant difference.

In total, 81 patients with 90 aneurysms underwent treatment using EP (n=43) or ST (n=47) SAC at the Department of Neurosurgery, Zhujiang Hospital, between January 2010 and January 2012. The characteristics of all the subjects are shown in Tables I and II. No statistically significant differences were observed with regard to age, gender, aneurysm size and location between the two groups. All the aneurysms (EP, n=39; ST, n=51) were successfully stented and coiled. Of these aneurysms, 74 (82.2%) were located in the anterior circulation, while 16 (17.8%) were located in the posterior circulation (Table III).

Inability to position the delivery system occurred with greater frequency in the EP group when compared with the ST group (P=0.022). In addition, the rate of technical complications in the EP group was significantly higher compared with that in the ST group (14.0 and 0%, respectively). Thus, the ST stent was more feasible to deploy (100%) compared with the EP stent (90.7%; Table IV).

Of the 43 aneurysms intended to be treated by SAC using EP stents, 39 (90.7%) were successfully stented and coiled. Two stent migrations occurred in the EP group following final deployment; in both patients this was managed by implantation of a second ST stent. In the remaining four cases where the EP stent was not navigable, the ST stent was successfully navigated without complications during subsequent coiling. In one of the four patients, the EP stent was unable to be expanded as desired, and the body of the stent experienced deformation towards the aneurysm sac subsequent to the stent being detached from the push wire (Fig. 1).

Of the 47 aneurysms intended to be treated with the ST stent, all were successfully deployed with subsequent coiling. The total success rate of ST-assisted coiling was 100%. However, in two patients, the stent required retrieval and repositioning subsequent to the initial full deployment. No patients experienced stent migration following the final placement in the ST group.

No statistically significant differences were observed in the procedure-related complication rates (P=0.228) and procedure-related mortality rates (P=1.000) between the EP and ST groups (Table IV). In the EP group, there was one case of a procedure-related complication (thromboembolic event), which occurred in the cavernous segment of the internal carotid artery and resulted in lower limb fatigue thereafter. In response, thrombolytic therapy was administered immediately following identification intraoperatively with urokinase. However, the patient exhibited little neurological improvement after six weeks of hospitalization.

In the ST group, five patients (9.8%) had aneurysms that were associated with procedure-related complications. The events included one thromboembolic event, one intraprocedure rupture, which was possibly caused by mechanical irritations during stent deployment, and three hemorrhages following SAC within one month, which were possibly associated with antiplatelet therapy and high blood pressure. Of these five patients, the patient who suffered the intraprocedure rupture succumbed, two patients with early hemorrhage events succumbed following surgery for non-endovascular events, while the other two patients (one thromboembolic event and one hemorrhage) survived.

Immediate angiographic results on the occlusion grade following the SAC were analyzed and the results are summarized in Table V. Complete occlusion was obtained in 19/39 (48.7%) of the EP group and 26/51 (51.0%) of the ST group. Neck remnants were present in 13/39 (33.3%) of the EP group and 15/51 (29.4%) of the ST group. In addition, a residual aneurysm was present in 7/39 (17.9%) of the EP group and 10/51 (19.6%) of the ST group. No statistically significant differences were identified between the two groups (P>0.05). Furthermore, the two groups achieved a high packing density, and no statistically significant difference was observed between the EP and ST groups (P=0.338).

At the most recent angiographic follow-up post-embolization, 29/39 (74.4%) of the EP group and 36/51 (70.6%) patients in the ST group underwent cerebral angiography. The mean follow-up times in the EP and ST groups were 15.9±11.4 and 14.0±6.8 months, respectively. Changes in the angiographic outcomes in the EP group were as follows: Stable in 16/29 patients (55.2%), progressive occlusion in 11/29 patients (37.9%) and recurrence in 2/29 patients (6.9%). Changes in the angiographic outcomes in the ST group were as follows: Stable in 21/36 patients (58.3%), progressive occlusion in 13/36 patients (36.1%) and recurrence in 2/36 patients (5.6%). In total, 24/65 (36.9%) aneurysms that were followed-up underwent progressive occlusion (Table VI). In the four cases that demonstrated an aneurysm sac, recanalization was observed without further treatment since the recanalization was minor. Each group had one patient that presented with an in-stent stenosis at the follow-up (EP, Fig. 2; ST, Fig. 3). The conditions of the two patients were observed during the first 12 months of the follow-up period and were asymptomatic; thus, further intervention was not required.