*7.1.1.2 Results of clipping procedures, associated complications and rescue measures*

Primary clipping of blister lesions is known to carry an up to 30% risk of complications, both intraoperative and postoperative [9, 49]. In the former group, aneurysm avulsion and internal carotid artery laceration seem to be our major concerns, while progression of the lesion often accompanied by rerupture seems to be the main danger during the postoperative period [50].

When confronted with a laceration of the carotid artery during surgery, the most commonly used rescue technique has traditionally been sacrifice of the vessel to control bleeding. As proven by numerous studies, this is associated with a high risk of cerebral ischemia, not only because collaterals may be inadequate in the first place but also due to hemorrhage-related vasospasm that often further aggravates the whole situation [16]. Other alternatives include direct suturing, placement of an encircling clip graft and reapplication of the originally placed clip to intentionally narrow the carotid artery and thus achieve hemostasis [4, 43]. In every case, surgeons must be always prepared for such an event, and large aspirators need to be available throughout the procedure. Initial hemorrhage control is usually achieved by applying direct pressure on the artery with oxidized cellulose and a small cottonoid. Brief periods of cardiac arrest with the aid of adenosine are also useful to improve visibility and help gain control of the situation [41].

Direct suturing of an arterial tear during surgery for a blister aneurysm is made possible because the edge of the lesion is relatively well outlined [51]. It entails removal of the original clip, trimming of the aneurysmal sac with microscissors (to prevent tissue buckling into the lumen) and repair of the arterial wall defect with

8/0 nylon stitches [43]. Suturing in the acute stage is usually extremely difficult due to the deep and narrow surgical field. As a result, initial attempts at this required prolonged trapping of the diseased segment invariably led to cerebral ischemia [52, 53]. To avoid this, recent studies propose reformation of the arterial wall with only a few stitches rather than its complete restoration [43]. Subsequent circumferential wrapping of the artery or, alternatively, placement of an encircling clip graft should be enough to stop oozing and stabilize the end result [54].

Encircling clip grafts have been developed by Sundt almost 40 years ago and specifically to address the problem of repairing the wall defect associated with a blister aneurysm [2, 55]. They can be used either as a primary modality (instead of the classic clip) or in cases of intraoperative rupture. Applied typically with the aid of a straight or right angle clip holder, Sundt clips provide a rigid sleeve and a soft woven fabric lining, allowing surgeons to essentially reconstruct the lacerated arterial wall [56]. Produced in various sizes, the appropriate clip for each case can be estimated on the basis of preoperative angiographic studies with a 3–4 mms diameter and a 3–5 mms length being the most widely used options [42]. Major disadvantages associated with these devices are that they cannot be used in cases of lesions close or opposite to carotid branches (i.e. posterior communicating and anterior choroidal arteries) and also that they come in certain fixed diameters that may or may not fit the vessel involved [48]. The latter limitation occasionally leads to postprocedural stenosis, a risk that surgeons must always be aware of and act accordingly [6]. Of note is a recent publication by Cho et al. who used a Sundt clip in combination with an endovascularly placed carotid stent to treat a ruptured blister aneurysm with good results [42]. Being a valuable adjunct in blister lesion surgery, encircling clip grafts should be readily available in all such procedures. Sadly, these adjuncts are rarely part of the modern day aneurysm clip tray, and young neurosurgeons are often not even aware of their existence.

Despite all efforts, intraoperative rupture of a blister aneurysm carries a mortality rate of up to 25% [57]. On this basis, and with surgeons trying for improved results, novel techniques continue to emerge. An interesting addition to our armatorium has been recently proposed by Kazumata et al. in the form of a protective bypass concept. According to these authors, when dealing with a blister aneurysm, and knowing the fragility of such a lesion, surgeons should at least contemplate an STA-MCA bypass prior to any attempted clipping. Ensuring adequate cerebral perfusion, this technique allows, in case of an intraoperative laceration, time for corrective measures to be applied accordingly. The duration of temporary occlusion for direct suturing or clip reapplication seizes to be a limiting factor, while, should the need for a carotid occlusion arise, this can be done safely, combined with a proper high-flow, radial artery graft bypass [58].

#### *7.1.2 Wrapping procedures*

In an effort to limit intraoperative manipulation of the lesion, neurosurgeons, especially in the past, have widely used wrapping of blister aneurysms as an alternative to clipping mode of treatment. In this context, wrapping is undertaken when a traditional clip cannot be properly applied due to either the morphology of the aneurysm itself or the underlying sclerotic changes of the parent vessel (i.e. the carotid artery) [46]. The technique entails encasing of the entire diseased segment of the carotid artery with an appropriately sized thin sheet of—usually—cotton. On occasions, cuts along its longitudinal axis are made to accommodate for branch vessels and perforators. Creation of ample room to allow free movement of surgical instruments and circumferential dissection of the aneurysm dome can prove dangerous but are, at the same time, essential. The wrapping material is applied with

#### *Blister Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.89284*

the aid of microforceps, and an angled clip is used to fit it snugly around the artery. Once the wrapping is secured, any excess length is cut and removed [39, 41].

The concept behind wrapping is that mechanical reinforcement of the diseased carotid artery provides protection from a potential rerupture during the immediate postoperative period while, in the long term, induced inflammatory changes eventually lead to connective tissue formation and remodeling of the weak arterial wall into a histologically competent structure [47, 59, 60]. Wrapping materials that have been tried out include muscle, muslin gauze, Teflon, silicon, collagen-impregnated Dacron fabric and cotton [46]. The latter seems to dominate today the relevant literature with most authors proposing it as the most effective option. Notably, Biobond, a cyanoacrylate glue widely used in the past, is by now obsolete due to its toxicity [60–62].

Complications associated with wrapping are rare. Perforator injury or parent vessel narrowing following placement of whichever material has been chosen make postoperative angiography an absolute necessity [63]. Delayed development of a granuloma or arachnoiditis has also been reported resulting in cranial neuropathies [64, 65], an observation that has led many authors to suggest that cotton must be used with the utmost care and never be placed in contact with adjacent cranial nerves, especially the chiasm [46, 63].

In the premicrosurgery era, numerous studies have been published on the efficacy and safety of wrapping. Among these, the largest series has been the one presented by Todd et al. in 1989. According to it, the risk of early (within 6 months) rehemorrhage after wrapping of an aneurysm has been calculated to be 8.6%, while late incidents were at 1.5% per year [66]. Results seem to have been significantly better after the introduction of the surgical microscope although only few relevant articles exist. Characteristically, Cudlip et al. reported in 1998 a series of 15 wrapped aneurysms with no rehemorrhages within 1 year after surgery [67].

Wrapping is unquestionably inferior to clip ligation for the treatment of ruptured aneurysms. However, it does offer a degree of protection during the immediate postoperative period, and, by doing so, it remains today a valid—even though last resort—therapeutic option when confronted with a blister aneurysm [47].

#### **7.2 Endovascular treatment**

Initial attempts at endovascular treatment with primary coiling of blister aneurysms (**Figure 3**) have returned, in most cases, disappointing results [68]. A high risk of intraprocedural rupture and coil protrusion or migration were problems commonly encountered due to the small size and shallow morphology of such lesions, their fragile nature and their proximity to vascular curves on the carotid wall (the latter, in combination with the typical orientation of blister aneurysms, has been known to necessitate a difficult and extremely gentle catheterization maneuver in order to gain access to the sac while avoiding a potential perforation) [19, 35]. Additionally, the lack, in many cases, of a true wall often allowed for posttreatment progression and—possibly—rebleeding [40]. As a consequence, most authors advocated that blister aneurysms are unsuitable for endovascular treatment and should therefore be left to surgery [69].

With the introduction of intracranial stents in clinical practice, our conception of blister lesion management has gradually changed. Surgical techniques are increasingly looked down upon as outdated and old-fashioned while stent-assisted coiling (**Figure 4**) became, initially at least, the new trend in the field. The procedure is carried out either by first placing the stent (e.g. Neuroform or Enterprise stents) and then introducing coils through its struts (trans-stent coiling) or by catheterizing the aneurysm sac and deploying the stent over the microcatheter

#### **Figure 3.**

*Simple coiling of a right ICA blister aneurysm. Intraprocedural images.*

#### **Figure 4.**

*Intraprocedural images showing stent-assisted coiling of a left ICA blister lesion.*

prior to coiling (jailing technique). Facilitating stable intrasaccular coil deployment while at the same time reinforcing the underlying diseased arterial wall, stent-assisted coiling promised to provide a safe and reliable therapeutic alternative [20, 70]. However, it was soon realized that results, even though better than those of surgery, were far from optimal. Intraoperative complications, mainly bleeding, were encountered in up to 17% of cases, while the risk for recurrence of the lesion, need for further treatment and postoperative repeat hemorrhage were reported at 65, 50 and 13%, respectively [9, 35, 71]. Notably, Meckel et al. found that the latter, a potentially catastrophic and fatal event, is seen only in cases that show incomplete occlusion (i.e. neck remnant or residual sac) by the end of the initial already procedure and especially if the patient receives full double antiplatelet treatment postoperatively or if the aneurysm in question is atypically large or partially thrombosed [35]. In this context, early and tight angiographic follow-up of partially obliterated lesions is essential, while any signs of regrowth should prompt complementary treatment. In the face of all these, most authors are by now moving away from stent-assisted coiling being the preferred primary and sole mode of treatment. Instead, they are using it, if possible, as a preliminary means to achieve a certain degree of protection until definite treatments, in the form of some other techniques, can be instituted.

Prior to moving on, and in order to close the discussion of stent-assisted coiling, it should be noted that one more major argument against it is the need for subsequent antiplatelet therapy [72]. This, combined with a potentially still unsecure aneurysm, requires careful consideration. Additional risks include the frequent

#### *Blister Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.89284*

need for a surgical intervention at a later time (e.g. extraventricular drainage or shunting procedures) [73, 74] and delayed spontaneous intraparenchymal bleeding with the rate of the later though not being affected by the initial subarachnoid hemorrhage [75, 76]. The exact therapeutic antiplatelet regimen that should be used in such a setting is still debatable. Some authors suggest that a similar to elective case scheme should be followed: loading with full doses of aspirin and clopidogrel just prior to the procedure, double antiplatelets for 3–6 months (usually 75 mg aspirin and 75 mg clopidogrel daily) and then continuation of only aspirin for another 6 months to life [77]. Going even further, Lee et al. augmented this regimen by a full-dose heparinization for 24–48 hours postoperatively [1]. On the contrary, other authors favor a reduced or even single-drug scheme. The rationale for this is that in the presence of a high-flow state within the stented lumen of large-size vessels (e.g. internal carotid artery), fibrin formation or clotting is relatively unlikely. Moreover, the risk of and the consequences of a potential intraprocedural rerupture are minimized, while at the same time occlusion of the aneurysm through thrombus formation is significantly facilitated. Using such an approach, Meckel et al. reported in 2011 only 1 fatal rehemorrhage in between 11 patients who were primarily treated with stent-assisted coiling of blister aneurysms. In other reports, stent-assisted coiling under systemic heparinization and loading with dual antiplatelets only after the procedure was found to be associated with a cumulative risk of thrombotic and hemorrhagic complications as low as 2% [78], while the intraprocedural use of aspirin and later introduction of clopidogrel carried a 21% overall risk of perioperative complications [79]. In any case, and because of significant heterogeneity of response to antiplatelet drugs, platelet function should be performed prior to any intervention as well as during the postoperative period (a patient's response may be found to change over time) [80, 81].

A recent development in blister aneurysm treatment and a welcome addition to our armatorium has been flow diversion. According to advocates of such a concept, and given that blister lesions are regarded by many as pseudoaneurysms, flow diversion is the only endovascular technique capable of actually reconstructing the vessel wall and sealing off any underlying defect [8, 82]. This can be achieved either through a stent-in-stent technique or with the aid of devices such as the pipeline or the Silk flow diversion systems. The former typically entails telescopic deployment of multiple overlapping stents within the diseased vessel in an effort to increase the total mesh density and thus restore proper parent artery laminar flow [8]. This results in thrombosis of the lesion, an effect augmented by endothelial proliferation along the length of the implanted stents. In the same direction, and specifically designed with this in mind, proper flow diverters like the Silk or the pipeline systems provide significantly better hemodynamic results at the expense however of increased perioperative complications due to their stiffness and thrombogenicity [83–85]. Notably, and regardless of the technique selected, flow diversion allows for preservation of branching vessels, an important feature when it comes to blister aneurysms since such lesions are usually located close to the posterior communicating or the anterior choroidal arteries [86].

Major concerns with the use of flow diversion for the treatment of blister lesions include an even more prominent need for antiplatelets as well as the fact that such an approach does not guarantee protection from postoperative progression and rerupture. Regarding the latter, and despite reports of a marked decrease in intraaneurysmal flow on the intraoperative already angiogram, hemodynamic stress upon the lesion theoretically remains at least for a few days [40]. Rasskazoff et al. recently reported that even with the use of double SILK flow diverters, complete occlusion of a blister aneurysm they treated did not occur till 18 days after the intervention, while Consoli et al. verified obliteration of a similar lesion no less than 6 months postprocedurally [8, 75]. A valid alternative possibly addressing the whole issue is the combination of flow diversion with coiling. On this basis, Kim et al. have reported favorable results with stent-assisted coiling as a primary treatment augmented by deployment of a second flow diverting stent if needed (i.e. postoperative progression of the lesion) [39]. In cases with extremely small lesions where coil deployment is perceived as carrying a significant risk, the reverse route can also be followed: telescopic stenting and subsequent trans-stent coiling should the lesion further grow to allow that [40]. Another attractive option involves covered stents; their use however is still limited due—mainly—to their stiffness, a feature that makes their intracranial delivery not only difficult but also dangerous since they may impinge on the fragile aneurysm neck portion resulting in intraoperative rupture. In addition, they often prove impossible to fully conform to the curved supraclinoid carotid wall, and, in this way, they can potentially leave an underlying aneurysm essentially open [39]. Whatever the case, further experience is needed should such devices gain a significant role in blister aneurysm treatment.

#### **7.3 Parent artery occlusion**

Although often considered as inherently inferior, deconstructive techniques allow for definitive occlusion of a blister aneurysm with minimal direct manipulation of its walls. In this context, carotid artery sacrifice and trapping of blister lesions significantly reduce the overall risk of rerupture during the perioperative period [19, 87].

Should carotid artery occlusion be contemplated as a final treatment, endovascular rather than surgical trapping is recommended due to its convenience, rapidity and safety. In an often cited article, Park et al. have described an elegant technique entailing the use of two microcatheters and a proximal balloon to control blood flow intraoperatively [19]. The first microcatheter is placed distal to the aneurysm, while the second is positioned just at the level of its neck. With the aid of the latter, and after inflation of the balloon, a framing coil is deployed inside the carotid artery. Prior to detachment, the distal microcatheter is retrieved and repositioned within the coil mess. Additional coils are deployed till a stable result is achieved. The use of trapping coils instead of detachable balloons is perceived as having a lesser risk of intraprocedural rupture.

When occlusion of the carotid artery is suggested, postoperative patency of its cardinal branches requires careful consideration. A detailed study of the ophthalmic, the posterior communicating and the anterior choroidal arteries as well as their collaterals is essential:

#### i. Ophthalmic artery

Blister aneurysms arise on the communicating segment of the internal carotid artery, and therefore the ophthalmic artery does not usually present a problem when dealing with such a lesion. If a choroidal blush via the external carotid circulation is visualized on preoperative angiograms, the trapped segment of the carotid artery is typically extended to include the origin of the ophthalmic artery as well, achieving thus a more robust result. As an additional precaution, proximal occlusion of the cervical internal carotid artery may also be performed. If, on the other hand, no ophthalmic collateral vessels are visualized, preservation of the ophthalmic artery is absolutely essential, and carotid trapping should be kept short. Accordingly, the proximal carotid artery cannot be occluded, and, as a consequence, close follow-up is mandatory to exclude recanalization of the trapped segment.
