Blood blister-like aneurysm (BBA) is often characterized with a fragile wall, a wide neck, and lack of distinguishable normal boundary between the aneurysm neck and parent vessel (1). Due to its special pathological features, neurosurgical treatment for BBA has been a big challenge compounded with the high odds of intraoperative rupture and postoperative recurrence. Different treatment modalities, including direct clipping, suturing, wrapping, coiling, stent-assisted coiling, multiple overlapping stents, and flow–diverter, have been applied for this terrible disease. Endovascular treatments have a lower risk of intraprocedural rupture but lower rates of aneurysm obliteration, while microsurgical treatments have higher rates of aneurysm obliteration but higher risk of intraprocedural rupture and subsequent ICA sacrifice (2–5). Among all these treatments, the most optimal management option for BBAs remains uncertain (1, 3–6).

In recent years, Willis covered stents (WCSs) have been specially designed for intracranial application, which brings a new option for the treatment of aneurysms, especially for BBAs (7). The WCS deployment has unique advantages compared with other treatments. It can isolate aneurysm and reconstruct the parent artery instantly without manipulations in the aneurysm (8). Several retrospective studies have evaluated the effectiveness of WCSs for BBAs with promising results (3, 9, 10). However, whether it is a reasonable choice for the BBA remains debatable considering the technical details. Here, we report our experience and evaluate the effectiveness in the treatment of BBAs of the internal carotid artery (ICA) with the WCS in 16 patients.

Although neurosurgical techniques and instruments have made great progress in the past decades. Both treatments for BBAs are still greatly challenging for neurosurgeons and neuroradiologists due to the special features of BBAs. Currently, the main treatment options for BBAs include surgical clipping, artery suturing, wrapping and clipping, stent-assisted coiling embolization, multi-stent implantation, and flow-diverting stents (2, 6, 14–17). However, a rescue or second treatment was required in 21% patients, and the overall morbidity and mortality rates were 17 and 15%, respectively. As endovascular treatment offers a lower procedural-related complication rate compared with surgical approaches, interventional therapy appears to be a more optimal treatment option for BBAs, with a more favorable patient outcome (16, 18). It should be pointed out that flow–diverter stent application in BBAs has achieved relatively more satisfactory results compared with traditional endovascular treatment in recent years (19–22). However, the lower rate of the immediate aneurysm occlusion and the use of antiplatelet agents make it controversial.

Since Li et al. first reported the treatment of intracranial pseudoaneurysms with a Willis coated stent in 2006 (7), more and more studies have reported the efficacy of WCSs in the treatment of BBAs, with the majority of patients having promising results (3, 9, 10, 23). The prominent advantage of WCS deployment is the immediate occlusion of aneurysms from the circulation, especially compared with the flow–diverter stents. Furthermore, the deployment of the WCS involves no manipulations focusing on the aneurysm cavity, thus reducing the risk of procedural-related rupture. As described here, all the 16 patients achieved immediate aneurysm occlusion after stent deployment, and no procedural-related rupture occurred. Compared with surgical procedures and other endovascular treatments, WCS deployment is technically simple and safe.

Although WCSs have many advantages, their limitations should also be considered. As WCS is stiffer than the ordinary stents due to its membrane characteristics and the microguidewire transportation system, its delivery is much more difficult than for another stent, especially during tortuous vascular access (24). Therefore, this stent is not recommended for the tortuous vascular approach. According to our experience, the combined use of an 8F guiding catheter and a 5F Navien support catheter is an optional choice. In most cases, we preferred to advance the 5F Navien beyond the aneurysmal neck to the M1 segment of the MCA; thus, WCSs could be delivered within the Navien to the target position. In some cases, with tortuous proximal vessels, a 5F Navien would be advanced to the C4 segment of the ICA for best support. Moreover, vasospasm, calcification, and stenosis should also be considered cautiously as they may increase the procedure risks. Vasospasm may influence the accurate selection for stent size while inappropriate stent may lead to poor stent apposition and aneurysm recurrence. Calcification and stenosis may influence stent delivery, balloon inflation, and stent apposition. As for the choice of stent length, branching and perforating artery occlusion is a major concern. Therefore, the appropriate size and deployment precisely of the cover stent is the key for the operation. For the clinoidal segment of the ICA, the OA, posterior communicating (PComA), and AChA are the three major arteries close to the BBA site. During WCS application, we tried our best not to sacrifice these arteries by choosing appropriate stents. The PComA was the primary concern in this study; if the PComA is absent or hypoplastic, it could be sacrificed without hesitation. As for the OA, because the deep and superficial anastomotic network will ensure the blood supply of the central retina artery, only a few patients experience blindness when OA is occluded (3, 25). The AChA provides the blood supply to many vital structures, including the posterior two-thirds of the internal capsule, adjacent optic nerve and auditory radiation, the medial portion of the globus pallidus, and the tail of the caudate nucleus (3, 26, 27). Acute occlusion of the AChA would result in catastrophic consequences that could not be predicted. In this study, the AChA was occluded in one patient owing to stent migration during balloon dilation. Although this patient had no neurological deficit after the treatment, he died several days later because of BBA recurrence and rebleeding.

As for the choice of stent diameter, endoleak is another major concern, although it is more likely to happen in an application for giant aneurysms (8, 10, 28). Endoleak issues may include stent shrinkage, inappropriate choice of stent, and irregular appearance of the parent artery. Based on our experience in preventing endoleak, a stent equal to or a little bigger than the artery in diameter is preferred. In this study, immediate endoleak was observed in two cases which were solved by balloon re-inflation with higher pressure in one case and deployment of a second stent proximally in another case. The significance of the early angiographic review should also be emphasized for WCS application to prevent BBA recurrence. In this study, one patient (see Patient No. 13 in Table 1) had aneurysm recurrence and serious re-hemorrhage the next day post-treatment, which was confirmed by angiographic review. Stent shrinkage caused by inappropriate selection of stent diameter might be the reason. Another possible reason may be the vasospasm caused by subarachnoid hemorrhage. The diameter of the parent artery may be not accurate. Therefore, when the vasospasm is relieved, the increase in the artery diameter may cause poor stent apposition. To our knowledge, the stent should be equal to or slightly larger than the target vessel in diameter. If the stent applied is smaller than the target vessel (although the balloon dilated with higher pressure), the stent might retract to its normal size and the covered membrane could not isolate the lesion, which would result in aneurysm recurrence and re-bleeding. Furthermore, the vessel spasm should also be cautiously considered in the measurement of vessels. As ipsilateral vessel spasm might be serious, we suggest referring to a contralateral vessel in diameter during measurement.

In this study, in-stent stenosis was found in one patient (see Patient No. 3 in Table 1) during the angiographic follow-up 6 months later. The main reason is that WCSs are more thrombogenic than the ordinary stents. Stent malposition may also increase the risk of in-stent thrombosis.

Although this study showed a promising result for WCS application in BBA treatment, there were still two major limitations. First, the long-term follow-up should be carried out to confirm the safety and efficacy of WCSs in BBA. Second, the number of patients was relatively small, and larger clinical trials are needed to confirm these results.

The WCSs may provide an alternative and effective solution for BBAs by aneurysm isolation and immediate ICA reconstruction. However, further follow-up studies with larger samples are required for confirmation.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

The studies involving human participants were reviewed and approved by Institutional Review Board, Tang DU Hospital. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

WF acquired and analyzed data, and wrote the first draft of the manuscript. JY, YL, and PS performed imaging analyses and acquired related data. ZY acquired clinical data. ZZ and YH contributed to the database. JD and TZ contributed to the conception and design of the study and reviewed the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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