Originally approved as a “bailout” in the event of coronary artery rupture, covered stents could reconstruct the vessel defects immediately while preserving the parent artery. Willis is the first covered stent exclusively designed for intracranial vasculature. In this paper, we shared our preliminary experience with this device for treating direct CCFs.
The goal of CCF treatment is to completely occlude the fistula while preserving the normal blood flow through the ICA. Traditionally, the treatment options include conservative treatment, surgical, and endovascular intervention [13]. Conservative management, consisting of external manual compression of the ipsilateral cervical carotid artery several times a day for 4–6 weeks, and CCF occlusion only occurred in only 17% of patients at 1-year follow-up [14]. Surgical intervention may involve suturing, clipping, or trapping the fistula, packing the cavernous sinus to occlude the fistula, sealing the fistula with fascia and glue, ligating the ICA, or a combination of these procedures. Overall success rates using surgical intervention in the treatment of CCFs have been reported at between 31 and 79% [13]. The high morbidity and mortality rates render surgical intervention only be warranted for patients in which endovascular intervention is not possible or unsuccessful. Nowadays, endovascular intervention has been the first-line therapy either via the trans-arterial or transvenous routes. Metallic coils, balloons, liquid agents, and more recently flow diverters are always used for occluding the cavernous sinus and fistula [15,16,17,18]. More than 80% of patients who undergo endovascular treatment for direct and indirect CCFs will experience a complete cure [13]. Compared with treatment modalities for CCFs with coils, Onyx, and balloons, the covered stent has some advantages: high overall complete occlusion rate, a relatively simple and rapid procedure, no coil herniation into the parent artery, no mass effect, and no CCF recanalization and recurrence. Of these advantages, the high overall complete occlusion rate is the most important [15]. However, there are also some limitations for covered stents in repairing vascular defects. First, small perforating vessel sacrifice restricts its usage. The absence of important branches at the cavernous ICA provides the feasibility of covered stents for direct CCFs. Second, the tortuous ICA makes the delivery of the stiff stent difficult. The Willis covered stent is designed exclusively for intracranial vasculature, aiming to overcome the inherent disadvantages of traditional covered stents [19]. Firstly, the abundance in versions with various diameters and lengths can accommodate target vessels of various sizes. Second, the unique structure design makes it more flexible for delivery. Third, the low inflation pressure of the balloon for releasing the stent decreases the potential of target vascular damage. Finally, the trackability of this stent has greatly improved than its congeners. A strong supporting system is necessary for delivering stiff covered stents [20]. We proposed an effective delivery system as described above, which was consisted of 8F guiding catheter, 5F Navien catheter, XT-27 microcatheter, and an exchanging microwire in co-axis. In our series, all stent deliveries with this system were successfully. In patient 3, unavailability of the soft Navien catheter lead to stent delivery failure. These results proved the necessity and efficacy of our delivering system.
From the economical perspective, detachable balloons are much cheaper than coils combined with liquid embolism in china with comparable complete occlusion rate and recanalization rate [21]. Others reported a higher recanalization rate of detachable balloons [22]. In our initial experience, the cost of using Willis covered stent for this disease is similar to that of coils combined liquid embolism. However, Willis covered stent harbor the advantage of no cavernous packing and resultant potential of cranial nerve injury. More cases are needed to further elucidate the economic issue for this novel device.
Defined as persistent perfusion of the space between the stent graft and parent vessel wall [23], endoleak occurred in 38.89% cases immediately after covered stent deployment [24], which was consistent with our cases (30%, 3/10). As major endoleak remained even after repeated balloon dilation and second stent deployment, we had to sacrifice the ICA with balloons in patient 2. In patient 10 (case 3, Fig. 3), endoleak diminished after re-dilation of the balloon and disappeared spontaneously at 6-month follow-up. In patient 4 (case 4), the endoleak was sealed with two coils via a pre-set microcatheter (Fig. 4). As we knew, this is the first report to pre-set a microcatheter for unexpected endoleak after stent deployment. As a pre-set microcatheter may induce a gap between the arterial wall and the stent leading to persistent endoleak, it is more reasonable to deliver the microcatheter via the venous route. Oblate vessel wall, diameter variance of the covered vessel, sharp bone fracture that stabbing the stent membrane, vasospasm, and stent diameter mismatch may contribute to immediate endoleak [24]. Balloon re-dilation and additional stent deployment were reported to solve this complication, and slight endoleak might disappear spontaneously in the follow-up [23]. The efficacy of these strategies was validated in patient 10 (case 3, Fig. 3). In this patient, the endoleak dramatically relieved after repeated balloon dilation, and the residual endoleak disappeared spontaneously at the 6-month angiographic follow-up. For patient 2, the parent artery was sacrificed as persistent endoleak despite repeated balloon dilation and second stent deployment.
In-stent stenosis was reported to occur in 18.0% and 20.9% of patients after Willis stent implantation at 2 and 6 years follow-up [24]. In our series, in-stent stenosis was seen in 1 case at 6-month follow-up (10.0%, case 3, Fig. 3). Smoking and stent angulation were predictors of late in-stent stenosis [24]. Repeated balloon dilation induced intima damage may contribute to the aggressive intima hyperplasia in this patient. Aspirin was prescribed and intermittent clinical follow-up was scheduled for him.
Recurrent or partially occluded CCF is always a nightmare for physicians, as the delivery of the microcatheter may be extremely difficult. Under this condition, a covered stent may serve as an alternative. In patient 8 (Fig. 2, case 2), the inferior petrosal sinus had already been occluded in the initial operation and a covered stent was selected as the salvage treatment. The fistula was occluded immediately after stent deployment.
