History and examination

A 20-year-old male patient was referred to our institute, for the treatment of a recurrent giant aneurysm of the proximal basilar trunk 3 months after coiling at another hospital. On admission, the patient complained of headache, blurred vision, numbness of the right-side of the face and left upper and lower extremities, as well as weakness of his upper and lower extremities for the past month. Neurological examination revealed no dysfunction but impaired superficial sensation on his right face and left upper and lower limbs. Catheter angiography showed no abnormality of the anterior circulation, but the posterior communicating arteries (PcoA) were absent. There had been interval spontaneous occlusion of intracranial V4 segment of the right vertebral artery, and a 43 mm × 31 mm aneurysm of lower basilar trunk supplied by left vertebral artery, with a 15 mm × 18 mm residual lumen and a 6 mm aneurismal neck. Diameter of the aneurismal afferent and efferent artery (relative to the aneurysm) was 3.5 mm and 4.1 mm, respectively. A robust inflow jet of the aneurysm was also noted, which was directed to the caudal right aspect of the aneurysmal sac so that the previously packed coils were compacted within the caudal portion of the aneurysm (Fig. 1).

Multidisciplinary decision

The main clinical and angiographic characteristics of the young patient were summarized as follows: (1) brainstem compression; (2) robust hemodynamic jet into the aneurysm with rapid recurrence and aneurysmal expansion within 3 months of coil embolization; (3) broad aneurismal neck of >4 mm; and (4) absence of good anterior to posterior circulation collaterals from PcoAs. Therefore, the objectives for treatment of the lesion were to exclude the aneurysm while preserving the parent artery and relevant perforators, to relieve mass effect, prevent hemorrhage, and avoid ischemic perforator and large artery stroke.

Open neurosurgery was considered, such as direct aneurysm clipping via a far lateral approach, or superficial temporal artery (STA) to superior cerebellar (SCA) or posterior cerebral artery (PCA) bypass plus distal occlusion of basilar artery just below the SCA via a subtemporal approach [1–6]. However, these procedures are extremely challenging for our neurosurgeons to perform with perceived high procedural risk.

Re-embolization with detachable coils was also considered, but the presence of pre-treatment mass effect was alarming. Additional coil volume and probable aneurysm expansion was deemed to be a high risk to result in increased mass effect. Further coil compaction due to the robust inflow jet was a concern as well. Coil sacrifice of the left vertebral artery alone was considered, however, the absence of PcoAs and pre-existent right vertebral artery occlusion would almost certainly result in complete posterior circulation infarction.

The Pipeline Embolization Device was not available at the treating institution. The remaining endovascular option was the use of a covered-stent with the Willis covered-stent (MicroPort, Shanghai, China). The Willis is a balloon-expandable polymer covered-stent with a nominating inflation pressure of 6 atm. A 3.5 mm × 10 mm size is available, which matched with the diameters of the parent vessel and the aneurismal neck in creating the SCRED.

Procedure and Periprocedural management

Written informed consent for this procedure was obtained from the patient and his family member. The institutional ethics committee approved the study protocol. Good Clinical Practice guidelines were used in accordance with the Declaration of Helsinki, and patient privacy was strictly protected. Consent from the patient for publication of this case study was also obtained.

After taking 75 mg clopidogrel and 300 mg aspirin daily for 5 days, the patient underwent the endovascular reconstruction procedure. Nimodipine (0.6 mg/h) was initiated intravenously to prevent artery spasm starting two hours before the procedure and maintained throughout the procedure. Heparin (3000 units) bolus was administered intravenously, followed by continuous at 1000 units/h, to maintain an activated coagulation time of approximately 220 s throughout the procedure.

The procedure was performed in our hybrid operating room equipped with an Artis Zeego angiographic system (Siemens AG, Forchheim, Germany). Under general anesthesia, a 6-French Neuron guiding catheter (Penumbra Inc., Alameda, USA) was advanced into the left vertebral artery. After 3-Dimension angiography, a 300 cm Transend microwire (Boston scientific corporation, Heredia, Costa Rica) and a Prowler SELECT Plus microcatheter (Codman Neurovascular, Chihuahua, Mexico) were negotiated across the aneurismal neck and reach the P2 segment of the right posterior cerebral artery under roadmap guidance. The guiding catheter was then advanced into the distal basilar artery over the assembly. The microcatheter was withdrawn while leaving the microwire in situ. The 3.5 mm × 10 mm Willis covered-stent was conveyed into the distal end of the guiding catheter over the microwire. After withdrawal of the guiding catheter from the basilar artery to the distal left vertebral artery, the Willis was unsheathed and adjusted to make sure that its proximal end was located at the afferent artery 2 mm below the proximal edge of the aneurismal neck, and its distal end at the efferent artery just about 2 mm over the distal edge of the neck. The Willis was then deployed by inflating the balloon to 6 atm. (Fig. 2a). The sub-complete aneurysm exclusion was immediately created, with an intentional endoleak at the distal end of the covered-stent, which reversed blood flow from the basilar artery distal to the Willis (Fig. 2b). To ensure complete artery wall apposition at the proximal portion of the Willis stent, the balloon was re-inflated to 8 atm after withdrawal of the balloon (6 mm) to the proximal portion of the stent. Angulation of the proximal basilar artery at the level of the intentional endoleak origin was also noted (Fig. 2b), which was likely to be unfavourable for blood flow redirection to the normal middle and distal basilar artery. Two 4.5 mm × 37 mm Enterprise self-expanding stents (Cordis Neurovascular, Miami, FL, USA) were telescopically deployed within the Willis stent from the mid basilar artery to the left vertebral artery (Fig. 2c), which changed the angulation sufficiently in the operators’ judgement (Fig. 2d).

Low molecular weight heparin (Dalteparin calcium 0.4 ml twice daily [Pfizer Manufacturing Belgium NV) was administrated for the first 3 postoperative days. Dual antiplatelet agents (75 mg clopidogrel and 100 mg aspirin daily) were scheduled for 24 months.

Clinical and imaging follow-up

There were no procedure-related complications or complications related to increasing mass effect. At discharge (20 days later), the patient’s headache had disappeared, and the other symptoms had also improved. The patient was asymptomatic at the 15-month follow-up.

Catheter angiography at 18 days (Fig. 3a), 3 months (Fig. 3b), and 15 months (Fig. 4) demonstrated that the aneurysm was completely excluded from the preserved vertebrobasilar artery, with dramatic reconfiguration of the previously “compacted” coils. On follow up, the coil mass was dense and closely apposed to the stent complex indicating aneurysm shrinkage. MRI T1WI (Fig. 5a), T2WI (Fig. 5b), and SPACE T1WI before (Fig. 5c) and after contrast enhancement (Fig. 5d) at 3 months also showed complete intra-aneurysm thrombosis.

A glimpse of the current management of giant basilar aneurysms

Giant aneurysms in the posterior circulation are aggressively managed because of high rupture risk of up to 50% at 5 years if left untreated. The aims of intervention are protection from hemorrhage, relief of mass effect and prevention of thromboembolism.

However, open neurosurgical approaches to giant basilar aneurysms are challenging due to the deep location, complex anatomy, and proximity to vital perforating arteries [1, 3, 4, 8–10]. Recurrent lesions post coil embolization may be especially challenging due to the presence of packed coils which may hinder tissue apposition and aneurysm exclusion during microsurgical clipping [6]. Risks of 10% mortality and 38% morbidity were reported in treating giant posterior circulation aneurysms by direct neck clipping and parent artery clipping with or without bypass [7].

Compared with coiling smaller aneurysms, coiling giant aneurysms is very challenging for endovascular approaches due to a lower rate of complete aneurysm occlusion and higher recurrence rates despite use of stent assistance. In a study of 39 giant aneurysms in 38 patients with coiling, cumulative mortality at 30 days and at mean 25 months of follow-up was 16% and 29%, respectively. The mortality was higher in posterior circulation aneurysms (20% [2/10] and 60%, [6/10], respectively), and highest in basilar aneurysms (40% [2/5] and 100% [5/5], respectively) [5].

Endovascular occlusion of the parent artery of giant vertebrobasilar aneurysms with or without bypass may be a better alternative for some selected patients. In a study of 13 giant vertebrobasilar aneurysms with good collaterals and tolerance to balloon test occlusion, parent artery coiling achieved a 92% rate of complete aneurysm occlusion. However, there still was one death and one recurrence during mean 28 months of follow-up [6]. Furthermore, parent vessel sacrifice without bypass is not suitable for patients with poor collaterals and failed balloon test occlusion.

The Pipeline Embolization Device has been approved in the treatment of large or giant wide-necked internal carotid aneurysms from the petrous to superior hypophyseal segments with extremely good outcomes, but the use of the device in vertebrobasilar aneurysms remains controversial due to uncertainty on safety [8, 9].

In 2002, Islak et al. proposed a partial exclusion concept with the use of covered-stent to manage a giant vertebrobasilar junction fusiform aneurysm [10]. In that case, a shorter covered-stent was navigated into a longer bare metal stent implanted across the aneurismal neck in advance, and deployed precisely covering the aneurismal inflow zone. The lesion was partially excluded immediately, and completely excluded at follow up 4 months later [10]. However, the concept is not generally accepted.

Our experiences in the current case

We modified the partial exclusion concept into one of sub-complete reconstruction with intentional endoleak distal to aneurismal neck, and successfully applied it in the current case of a symptomatic recurrent giant basilar aneurysm after coiling. The SCRED was safely and effectively created immediately, and resulted in complete vascular reconstruction at an early time point, with gradual disappearance of symptoms.

Two main observations are discussed as follows:

First, the SCRED was immediately achieved as the patient’s efferent artery was larger than his afferent artery, which is a prerequisite of creating the reversed blood from the distal end of parent artery with the use of a balloon-expandable covered-stent; and the covered-stent used was well matched in size with the afferent artery, efferent artery and aneurismal neck. So, precisely measuring the 3 key diameters and choosing the appropriately sized covered-stent in advance are crucial when applying the SCRED concept to reconstruct vasculature. Additionally, the coaxial deployment of the Enterprise self-expanding stents inside the covered stent may have played an important role for early aneurysmal exclusion and complete vascular reconstruction, by decreasing the angulation of the proximal basilar artery, and directing the blood flow away from the aneurysm.

Second, the aim of protecting side branches and perforators was achieved as well, as intended. Covered-stent implantation can effectively exclude giant aneurysms from the patent arteries with no need of coil embolization, and in turn, may play a role in protection from delayed hemorrhage while relieving mass effect [10]. However, covered-stents may isolate perforators originating from the arterial segment covered by the covered-stent, and subsequently lead to perforator strokes and even fatal perforator strokes [8, 9]. Perforating arteries are plentiful in the basilar artery, with a caudal group comprised of 2 to 5 perforators, a middle group with 5 to 9 perforators, and a rostral group with 1 to 5 perforators. Though the distal end of the covered stent was deployed in the caudal basilar artery, the arterial wall apposition was deliberately incomplete in this segment, so that our patient remained well at the follow-up of 15 months, suggesting that the reversed blood flow was sufficient to supply the caudal group perforators.

The outcome of our case was satisfactory, but further in depth studies are needed to realize the exact function and role of a “SCRED” and the durability in the treatment of giant basilar trunk aneurysms.

Sub-complete reconstruction with intentional endoleak distal to the aneurismal neck was safely achieved after implantation of covered-stent and conventional stents in the case of giant post-coil recurrent proximal basilar aneurysm, with subsequently complete vascular reconstruction. Evaluation of safety and efficacy, and indications for this technique require further study.