Flow-T stenting with the Silk Vista Baby and Baby Leo stents for bifurcation aneurysms – A novel endovascular technique

Abstract

We present the first case using a novel flow diverter, the Silk Vista Baby (Balt, Montmorency, France), in combination with a low-profile braided stent, the Baby Leo (Balt, Montmorency, France), in a T configuration that we term Flow-T. We describe the technical characteristics of the case as well as the early follow-up results. We believe that this combination may provide an alternative to standard T-stenting and alternative to treat bifurcation aneurysms.

Introduction

Wide neck bifurcation aneurysms (WNBAs) pose a challenge in endovascular treatment. A wide variety of different treatment strategies have been developed to deal with WNBAs including balloon-assisted and/or stent-assisted coiling and the waffle cone technique.^1–7 More recently, dedicated devices such as the pCONus1, pCONus2 and pCANvas (phenox, Bochum, Germany), the Pulserider (Pulsar Vascular, Los Gatos, California, USA) and the eCLIPs device (Evasc Medical Systems Corp.) have entered the market. These devices share the common feature of providing extra coverage at the aneurysm neck to prevent coil prolapse into the parent vessel. Intra-saccular devices such as the WEB (Microvention, Aliso Viejo, California, USA) represent an alternative technique.^8–10

A stent-assisted coiling technique, known as T-stenting, has shown promise in the treatment of WNBAs. The development of low-profile braided stents, such as the Baby Leo (Balt, Montmorency, France), that can be deployed through low-profile 0.17 in. microcatheters have made this strategy feasible. The recent introduction of low-profile flow diverters specifically designed to target smaller calibre vessels and deployed through 0.17 in. microcatheters has allowed an adaptation to the standard T-stenting technique. In this case, we describe the first case of Flow-T stenting using a combination of the Silk Vista Baby (SVB) flow diverter (Balt) and a Baby Leo stent.

Case

A 42-year-old female patient with no background medical conditions presented to the emergency department with a one-day history of severe headache and photophobia of acute onset. On admission, she was apyrexial, in sinus rhythm and normotensive. A subarachnoid haemorrhage (SAH) was suspected and was confirmed on an unenhanced computed tomography (CT) scan with a small amount of SAH seen in the left Sylvian fissure. A CT angiogram demonstrated a partially thrombosed aneurysm of the left middle cerebral artery (MCA) bifurcation that was later confirmed on catheter angiography (Figure 1).

After discussion with the neurosurgical team and the patient, stent-assisted coiling was decided upon. Given the acute presentation, the patient was not pre-loaded with anti-platelet agents.

After general anaesthesia, the patient was given a loading dose of aspirin (500 mg IV) and prasugrel (60 mg) via the nasogastric tube (NG tube). After ultrasound-guided micropuncture of the right radial artery and insertion of a 6Fr sheath, the left internal carotid artery was accessed using a Benchmark and Simmons Select catheter (Penumbra Inc., Alameida, CA, USA). Angiography demonstrated the complex, multi-lobulated aneurysm of the bifurcation of the MCA that was felt to be dissecting in nature. There was no evidence of dissection elsewhere and no features to suggest an underlying connective tissue disease. Under full heparinisation and maintenance of the activated clotting time at 2–2.5 times, normal catheterisation of the intracranial vessels was performed. Using a Headway 17 Soft microcatheter (Microvention, Tustin, CA, USA) and Synchro 2 wire (Stryker Neurovascular, Kalamazoo, MA, USA), the ascending frontal artery complex was accessed followed by catheterisation of the aneurysm using an Echelon 10 microcatheter (Medtronic, Dublin, Ireland). Immediately prior to deployment of the SVB a bolus dose of integrilin (10 mg) was given. After deployment of the SVB, several coils were placed in the aneurysm dome. Subsequently, the Headway microcatheter was used to catheterise the angular artery, and a Baby Leo stent was deployed. The stent was compressed across the neck of the aneurysm, but compression at the opening of the SVB flow diverting stent (FDS) was avoided (Figure 2). There were no intra-operative complications and the patient awoke at baseline neurology. The patient was discharged two days post-operatively on aspirin 75 mg and prasugrel 10 mg per day for six months followed by aspirin alone for life as is our standard protocol.

Early angiographic follow-up at six weeks showed the aneurysm to be excluded from the circulation (Figure 3). There was equal and symmetrical flow in the stented branches. Clinically, the patient was at baseline neurology and mRS 0.

Figure 1.

A small amount of subarachnoid haemorrhage was seen within the left Sylvian fissure (a) on the unenhanced CT scan, and on closer examination, there appeared to be a high-density mass that was thought to be a partially thrombosed aneurysm (b). CT angiography confirmed the presence of an irregular lobulated aneurysm at the middle cerebral artery bifurcation (c) that was subsequently confirmed on catheter angiography (d and e, white arrows).

Figure 2.

The Headway Soft microcatheter was first used to catheterise the ascending frontal artery, following which the aneurysm was catheterised with an Echelon microcatheter. After deployment of the Silk Vista Baby (SVB) (a), several coils were placed into the aneurysm dome (b). The Headway was then used to catheterise the angular artery, and a Baby Leo was deployed with careful attention to compress the Baby Leo only across the neck of the aneurysm and not across the opening of the SVB. Angiography at the end of the procedure confirmed vessel patency throughout.

Figure 3.

Follow-up angiography at six weeks post-op showed stable exclusion of the aneurysm and symmetrical flow within the stented branches as well as preserved flow in the branches covered by the stents.

Discussion

The T-stenting technique was originally described by Cho et al.¹¹ in 2012. They described, what was originally called the non-overlapping Y-stent technique, the use of this configuration with two closed cell stents to treat six basilar tip aneurysms. Aydin et al.¹² published their mid-term results of the T-stent-assisted coiling of WNBAs. They identified 24 patients with 24 aneurysms that were most commonly located at the MCA bifurcation and the Acom. The Baby Leo (Balt) low-profile braided stent was deployed in all but one vessel. The technical success rate of the procedures was 95.8%. There was a single technical complication in a single case, in which the stent deployed into the long arm did not fully appose the arterial wall and required balloon angioplasty. Immediate aneurysm occlusion was graded as Raymond-Roy classification I in 19 cases (79.2%), grade II in 4 cases (16.6%) and grade III in a single aneurysm (4.2%). At follow-up, which was available in 22 patients and at an average of 9.3 ± 4.8 months post-procedure (range 3–24 months), grade I occlusion was seen in 18 patients (81.2%) and grade II in 4 patients (18.2%). In the five patients originally determined as having grade II or III aneurysm occlusion immediately post-operatively, angiographic improvement was seen in two cases (40%). Recanalisation, that has not required further treatment, occurred in a single case (4.5%). Cheung et al.¹³ recently reported their long-term follow-up of patients treated with braided stents using the T and Y stent configurations. They identified 17 patients that underwent either T (n = 15) or Y stenting (n = 2). The authors reported adequate occlusion, defined as grade I or II on the modified Raymond Roy occlusion scale, in 88% of patients at the end of the procedure, which increased to 94% (n = 15/16) at 18-month follow-up. There was also a shift from grade II occlusion to grade I occlusion over time with only 41% of patients having grade I occlusion at the end of the procedure (n = 7/17), whereas 79% (n = 11/16) had grade I occlusion at 18 months. These results suggest that traditional T stenting with braided stents is an effective technique for the treatment of WNBAs and that the aneurysm occlusion appears to be stable over time.

Y-stenting represents an alternative technique for bifurcation aneurysms and has been more extensively studied. Recently, Granja et al.¹⁴ performed a systematic review and meta-analysis of the Y-stenting technique. Their study included 18 studies with 327 patients, with 343 aneurysms, the majority of which were in female patients (n = 193, 64%). The majority of the aneurysms were classified as small (<10 mm). The vast majority were wide necked (89%) with the mean aneurysm neck size being 5.2 ± 0.2 mm. Aneurysm location was reported in 310 cases with 44% of the aneurysms located in the posterior circulation. The overall rate of complete aneurysm occlusion at follow-up was 91% (n = 203; 95% CI 88–95%) with no significant differences in terms of favourable occlusion rates seen between aneurysms measuring <10 mm and those >10 mm (55% vs. 58%, p = 0.223). The rate of permanent neurological deficit was 4% (n = 10, 95% CI 0.2–4.5%), and procedure-related mortality was 2% (n = 7, 95% CI 0.6–3.8%). These results are heavily influenced by the sub-group of patients treated for basilar artery bifurcation aneurysms who demonstrated occlusion rates of 60% (n = 52; 95% CI 49–70%) and a stroke rate of 8% (n = 7; 95% CI 2–13%).

Neurosurgery would have represented a potential alternative treatment; however, as we believed that the aneurysm was dissecting in nature, the treatment may have been complicated and involve bypass rather than simple clipping. Chung et al.¹⁵ reported on their series of 416 unruptured MCA bifurcation aneurysms treated for 11 years and they reported an overall complication of 3.6% (15 of 416) with two-thirds of these being asymptomatic; however, the authors note that only 3 (0.7%) giant and 28 (6.7%) large aneurysms were included in their series. Similar results have been reported by other groups.¹⁶

Flow-T stenting represents an advancement of the traditional T-stenting technique that has recently become an option thanks to the development of low-profile FDSs, such as the SVB (Balt) and the p48 (phenox, Bochum, Germany). These new devices can be passed through 0.17 in. microcatheters such as the Headway (Microvention, Tustin, California, USA) that makes access into small calibre daughter branches easier and safer. The use of the flow diverter in the short arm, as in our case, is optimal in our opinion. Placement of the flow diverter in the long arm would effectively be the same as the use of flow diversion for bifurcation aneurysms, the results of which have been mixed^17–21 and should be avoided. The placement of the FDS in the short arm will allow maximal coverage of half of the aneurysm neck. Furthermore, the FDS will go to nominal diameter across the neck of the aneurysm and optimise the flow diversion away from the aneurysm, whereas this would be less effective if the braided stent were placed in the short arm since the porosity is higher. One difficulty we have observed with the placement of the FDS is accurate positioning. There is considerable foreshortening of the device across the aneurysmal neck, and therefore recapture and repositioning may be required in order to optimally position the FDS and a longer than expected stent may be required. The SVB can be re-sheathed up to 90% deployment, and this feature aids significantly when accurate positioning is required as in our case. Compression of the braided stent at the neck of the aneurysm will allow maximal coverage of the aneurysm neck. Then by unsheathing the stent as it is deployed across the opening of the short arm FDS, the pore size will increase around the outer curve²² and allow flow into the FDS (Figure 4). In this fashion, a ‘bifurcation flow diverter’ can be created. Adjunctive coiling can also be performed, and although this technique theoretically has the potential to treat bifurcation aneurysms without coiling, this remains to be proven. To date, there are limited data available regarding the SVB; however, the published results are promising.^23,24

Figure 4.

The flow diverting stent (FDS) is placed in the short arm with coverage across the aneurysm neck (double headed white arrow) first. Accurate placement can be tricky as the FDS may foreshorten significantly as it opens up across the aneurysm neck. The braided stent is placed in the long arm and should be compressed across the aneurysm neck (double headed black arrow). Compression of the braided stent across the opening of the FDS should be carefully avoided to allow flow into the side branch (dashed double headed white arrow). This allows the construction of a ‘bifurcation flow diverter’. Coils can be placed in the aneurysm.

Conclusion

This is the first case to demonstrate the use of a low-profile FDS in combination with a braided stent to treat a complex bifurcation aneurysm. This technique, which we have called Flow-T, may have advantages over traditional T-stenting and the use of FDSs to treat bifurcation aneurysms. It is important to implant the FDS in the short arm and the braided stent in the long arm of the T to optimise the properties of both devices and the chances of success.

Declaration of conflicting interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: PB is a consultant for phenox.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.