Written informed consent was obtained from all participants. In addition, our local institutional ethics review board (the Medical Ethics Committee of Second Military Medical University) approved the research protocol for the retrospective study. Participants of the current study also agreed with publication of their personal information for research purposes.
From July 2009 to August 2013, 357 patients whose CTA/MRA confirmed severe stenosis (>70 %) were admitted to our department for further diagnostic cerebral angiography. Among them, 298 patients demonstrated severe stenosis (>70 %) and were treated by percutaneous transluminal angioplasty and stenting (PTAS: 34 with the Solitaire stent; 137 with the Wingspan stent; and 83 with domestic stents). Of the 298 patients, 44 patients were treated with the Enterprise stent and met the following inclusion criteria: (1) stenosis >70 % as determined by digital subtraction angiography (DSA) using the formulas described by the Warfarin Aspirin Symptomatic Intracranial Disease (WASID) method; (2) recurrent low-flow TIAs or non-disabling ischemic stroke despite antiplatelet or anticoagulation therapy (at our center, patients with symptomatic ICAS undergo close outpatient follow-up and aggressive medical management according to the guidelines for the prevention of stroke in patients with stroke and TIA); and (3) stenoses located in lesions that are long, at a bifurcation, and/or with tortuous access, and therefore particularly challenging for Wingspan stent use because of its rigidity. Patients with any of the following were excluded: (1) total occlusive lesion; (2) severe disability because of stroke or dementia; or (3) inability to give informed consent.
All patients underwent cerebral angiography to confirm the diagnosis, and three-dimensional reconstruction was performed to accurately measure the morphology and access of the targeted segment of stenosis. The measurement of normal and stenotic vessel diameter was performed using the two-dimensional angiographic image with the help of a measuring ball, and the degree of stenosis was calculated with the formulas described by the WASID method . We used the LMA classification  that Jiang et al. described to identify the location, morphology, and access of intracranial stenosis. Among the 44 lesions studied, 24 were located in the middle cerebral artery, one in the anterior cerebral artery, 8 in the intracerebral vertebral artery (VA), and 11 in the basilar artery trunk. The average vascular lesion length was 11.64 ± 6.33 mm (range, 4.20–28.00), and the mean reference artery diameter was 2.63 ± 0.79 mm (range, 1.52–4.01). Stenosis was located adjacent to bifurcations in 28 (63.6 %) patients.
A dose of 300 mg of acetylsalicylic acid (ASA) and 75 mg of Clopidogrel was given at least 3 days before endovascular treatment, which was always performed under general anesthesia. A 6 F guiding catheter was introduced through a femoral sheath. During intervention, patients were heparinized to a doubled activated clotting time. A radiologic examination of the target vessel was performed using a biplane angiographic system (Artis zee Biplane; Siemens, Erlangen, Germany) or a single-arm angiosuite (Philips FD, Netherlands). Rotational angiography followed by 3D reconstruction was performed to understand the normal vessel diameter adjacent to the stenosis and the diameter and the length of the stenosis. The enhanced Dyna CT was also performed to access the location of the plaque and the relationship between the stenosis and important vessel branches. Under a road-map, the vessel distal to the stenosis was catheterized with Transcend Floppy microguidewire (Boston, Scientific), followed by predilatation with a balloon (Gateway, Stryker). After deflation and withdrawal of the balloon catheter, a flushed 0.021-inch microcatheter (Prowler Select Plus, Codman) was navigated over the exchange-wire. The Enterprise stent (Codman) was deployed to cover the targeted stenosis. A daily dose of aspirin (300 mg) and clopidogrel (75 mg) was recommended for 6 weeks after discharge followed by only aspirin. We did not perform routine response testing for aspirin or clopidogrel mainly because of cost and coverage constraints. Treatment for hypertension, and to normalize blood glucose and lipid levels if needed was also suggested. All patients received statin therapy after stenting, 30 (68.1 %) patients with hypertension were treated with antihypertensive drugs, and 13 (29.5 %) patients with diabetes mellitus received either metformin or insulin therapy.
Evaluation of outcomes and clinical and angiographic follow-up
The primary outcome for this study was occurrence of any stroke or death during/after the procedure and at 30-day follow-up. Secondary outcomes were procedural success, occurrence of >50 % in-stent restenosis confirmed by DSA, and occurrence of transient ischemic attack (TIA) or stroke attributable to the target vessel during the follow-up observation period.
Procedural success was defined as accurate delivery and deployment of the stent (in all intended stenting procedures), covering the target lesion completely and resulting in a residual stenosis of less than 50 %.
The neurological status was documented according to the National Institute of Health Stroke Scale (NIHSS) score at discharge. A TIA was defined as neurological worsening with complete recovery within 24 h. Minor and major stroke was defined as persistent worsening of the NIHSS score of <4 or ≥ 4 points, respectively. We defined symptomatic brain hemorrhage as parenchymal, subarachnoid, or intraventricular hemorrhage detected by CT or MRI that was associated with new neurological signs or symptoms lasting 24 h or more or a seizure. The initial and follow-up clinical evaluations were performed by two neurologists (P Zhang and L Chen).
Angiographic follow-up was scheduled at 3 and 6 months and yearly thereafter with DSA, CTA, and/or CTA/CTP. DSA was routinely used to assess restenosis, and although image might be affected by stent-related artifacts, CTA was used when patients refused invasive assessment. ISR was defined as >50 % stenosis within or immediately adjacent (within 5 mm) to the implanted stent with >20 % absolute luminal loss in 2D-DSA image.
Statistical analyses were performed using SAS 9.1 (SAS Institute Inc., Cary, NC). Mean, median, and standard deviation were used for descriptive statistics. Differences between before and after treatment were analyzed using the t- and chi-square tests for parametric and nonparametric data, respectively. P < 0.05 was considered statistically significant.