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.
|Localization||Nonbranching site, proximal|
|Dimension||Small, 3 mm (within 24 hours of SAH)|
|Shape||Conical, wide neck|
|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.
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.