Blister-like aneurysms

Blood blister-like aneurysms (BBAs) are small sidewall aneurysms, first described in 1986 as “chimame” (blood blisters) given their particular morphology, that arise from non-branch points of large intradural arteries; they can grow in many sites: the supraclinoid segment of the ICA is the typical location, but they can grow atypically in the middle cerebral artery, anterior communicating artery, basilar artery, and posterior cerebral artery (7.8% of all BBAs). BBAs account for 0.5-2.0% of ruptured intracranial aneurysms and lead to unusually high morbidity and mortality rates; they may not be visible to the first angiographic studies but may enlarge over a few days.

clipped BBA

Characteristics Description
Localization Nonbranching site, proximal
Dimension Small, 3 mm (within 24 hours of SAH)
Shape Conical, wide neck
Appearance Dissecting
Tendency to rebleed High, due to friable walls
Tendency to grow High

BBAs of the supraclinoid ICA are characterized by an hemispheric and broad-based appearance without a neck, an extreme instability and a tendency to rupture or regrow.

The few reports of histological examinations have found absence of the internal elastic lamina and smooth muscle with a wall consisting of adventitia and fibrous tissue only without changes suggesting dissecation. Since most are diagnosed after SAH, It was suggested by Abe et al. that the effect of an adjacent subarachnoid blood clot causes rapid growth.

BBAs tend to rupture at an earlier patient age and at significantly smaller size compared to typical saccular aneurysms. Because they are extremely fragile lesions without definable neck, treatment is difficult and intraprocedural rupture is common, occurring in nearly 50% of cases.

In 2015, Bojanowski et al. proposed a classification of BBAs that provides some indications of the therapeutic options for treating BBAs based on their morphological features:

  • Type I: simply BBAs with a small bulge.
  • Type II: BBAs resemble a saccular aneurysm and involve part of the ICA wall. A small portion of the healthy artery wall must be included when type I and II BBAs are clipped.
  • Type III: BBAs involve a larger longitudinal portion of the ICA.
  • Type IV: BBAs involve almost the entire ICA circumference.

Clipping of BBAs type I and II include a small portion of the healthy artery wall; type III BBAs require the application of 2 clips in tandem and in type IV BBAs clipping after wrapping technique is required.

Growing BBA

Tiefeng Ji et al. proposed a therapeutic protocol for BBAs of the supraclinoid ICA; they suggested that before treatment, the most important things to consider are: the risk of complete or partial occlusion of the supraclinoid ICA related to the treatment and the collateral circulation of the internal carotid artery. With good collaterals, all available surgical or endovascular treatments are feasible, even occlude the ICA. But in the acute stages of SAH, ICA sacrifice without cerebral revascularization results in extremely poor outcomes and needs protective EC-IC bypass. With poor collaterals, a bypass between the external carotid artery (ECA) and ICA and trapping of the supraclinoid ICA is a good treatment choice. Therapeutic methods that will not reduce blood flow in the ICA, like flow diverter stents (FDs) are alternative treatment options.

Surgical treatments

Clips position depends on BBAs location: if BBA is located at the dorsal supraclinoid ICA, clips are placed parallel to the ICA, incorporating a thin band of tissue from the healthy arterial wall, if BBA is small and located at the ventral supraclinoid ICA, clips are placed perpendicular to the ICA or across the ICA, with the encircling clip applied to the medial artery wall. Cotton is often placed on the BBA before it is clipped to increase the friction force and prevent the clip from slipping.  However, even in the best of hands, direct clipping of ruptured BBAs carries a 3050% risk of intraoperative rupture, suggesting that direct clipping should not be the first-line treatment, perhaps with the exception of Bojanowski type I and II.

Suturing the BBAs or repair it with vascular closure staple clips could be also a good choice and clipping after suturing should be safer than suturing alone if the defect is small.

The clipping after wrapping technique has been used as the optimal surgical modality to prevent rebleeding from BBA lesions because a large case study showed that this technique resulted in good outcomes. This technique allowsto secure various materials (muscle fascia, cotton, cellulose fabric, or Gore-Tex) wrapped around the entire circumference of the ICA to reinforce the vessel wall.

The preoperative balloon occlusion test or compression test should be performed to examine the collateral circulation.

1998 Abe et al. 1 BBA case of rebleeding due to clip displacement from the ICA; then the BBA was sutured
2002 Yanaka et al. 1 BBA case treated with clipping after suturing; BBA was covered with Surgicel and fibrin glue
2004 Yanagisawa et al. 1 BBA case treated with vascular closure staple clips
2006 Sim et al. 6 BBA cases treated with simple clipping; clips displacement in 2 cases
2009 Otani et al. 4 BBA cases treated with simple clipping
2009 Vashu et al. 2 BBA cases treated with simple suturing
2009 Lee et al. 15 BBA cases treated with clipping after wrapping using cellulose fabric
2010 McLaughlin et al. 7 BBA cases treated with simple clipping and angiographic stenosis of the ICA without symptoms
2015 Yu et al. 9 BBA cases treated with simple clipping and angiographic stenosis of the ICA without symptoms
2016 Kantelhardt et al. 1 BBA case treated with micro-sutures and mini-clips for vessel wall adaptation

Endovascular treatments

Endovascular techniques have evolved as an effective treatment for intracranial BBAs and in some studies they were associated with high rates of complete occlusion and good mid- to long-term neurological outcomes.

Due to its characteristics, simple coiling of ruptured BBA is almost impossible and stent-assisted coiling (SAC) is needed; moreover, stent endothelialization can cover the BBA neck. This technique facilitates placement of coils, but is associated with low occlusion rates: 33% initially and around 70% at mid- to long-term follow-up. Furthermore, SAC may be difficult and have potential associated risks, including aneurysm neck disruption or distal coil migration, microcatheter or microwire perforation and the only advantage of coil embolization of BBAs is that antiplatelet therapy is not needed. Some Authors suggest a delayed treatment, because in late stage BBAs may be covered by a thick clot, which improves their stability. In contrast a delayed treatment could be fatal due to the high risk of rebleeding of BBAs.

Based on the computational demonstration that placement of overlapping stents at the aneurysm neck diminishes the flow into the artery better than a single stent, some authors demonstrated that this technique is a safe and effective strategy. The multiple overlapping stents technique entails the deployment of longer and shorter stents at the level of BBAs neck. But currently the number of stents required for an effective treatment is unclear and the antiplatelet treatment necessary in this treatment may increase the risk of recurrence of BBAs and postoperative rebleeding, if BBA occlusion is not immediate.

Because of the purely endoluminal arterial reconstruction, FDs represents an appealing option for BBA repair and several clinical series have lent support to this concept. These self-expanding stents have high metal surface area (30-35% metal coverage) and after covering the neck of the aneurysm, induce stasis, thrombosis, and regression of the aneurysm. In meta-analyses, use of FDs carries a lower retreatment rate (7 vs 27%, p < 0.001) and a higher occlusion rate than stenting with or without coiling, both initially (36 vs 33%, p = n.s.) and in the mid- to long-term (91 vs 70%, p < 0.01). Like for the open cell stents, the dual antiplatelet regimen may increase the risk of recurrence of BBAs and postoperative rebleeding.

2004 Tanoue et al. 1 BBA treated with simple coiling 40 days after admission; complete obliteration was obtained
2006 Ezaki et al. documented the evolution of BBA that became saccular after 15 days from aSAH; simple coiling after 19 days
2006 Fiorella et al. 2 BBAs one treated with single stent and one with three overlapping stents; obliteration in both cases
2007 Kim et al. 1 BBAs treated with double stent-assisted coiling
2008 Korja et al. 1 BBAs treated with stent-assisted coiling in acute phase
2008 Doorenbosch et al. 1 BBAs treated with stent-assisted coiling two weeks after admission
2008 Ahn et al. 1 BBAs treated with stent-assisted coiling after several simple coiling
2009 Lee et al. 3 recurrent BBAs initially treated with stent-assisted coiling; treatment with a second covered stent and one patient died during the procedure
2010 Gaughen et al. 6 BBAs treated with two overlapping stents
2011 Matsubara et al. 9 saccular BBAs, 7 treated with balloon-assisted coiling and 2 with simple coiling
2011 Kim et al. 3 BBAs treated with multiple overlapping stents
2012 Ihn et al. 6 BBAs treated with stent-assisted coiling; early re-hemorrhage in 2 cases
2013 Lim et al. 34 BBAs treated with stent-assisted coiling; they suggested that ventral BBAs of the supraclinoid ICA tend to occlude progressively, even after an incomplete occlusion, whereas dorsal BBAs tend to recur and must be observed carefully
2013 Chung et al. 1 case of BBAs rebleeding after treatment with 5 overlapping stents
2013 Çinar et al. 7 BBAs treated with Pipeline
2014 Walsh et al. 8 BBAs treated with multiple overlapping stents
2014 Chaloui et al. 8 BBAs treated with Pipeline
2014 Hu et al. 3 BBAs treated with Pipeline
2015 Nerva et al. 1 BBAs treated with two telescoping Pipeline
2015 Aydin et al. 3 BBAs treated with two telescoping Pipeline
2016 Song et al. 10 BBAs treated with multiple overlapping stents (≥3)
2016 Linfante et al. 10 BBAs treated with single Pipeline; growth in two cases without rupture
2016 Lozupone et al. 8 BBA case treated with an FD
2018 Hao et al. 8 BBA case treated with the endovascular patch embolization method

Blister Aneurysms of the Internal Carotid Artery: Microsurgical Results and Management Strategy

Blood-blister like aneurysm of the supraclinoid internal carotid artery