Morphological aspects of blister aneurysms and nuances for surgical treatment

OBJECT

Blister aneurysms of the supraclinoid part of the internal carotid artery (ICA) are known for their high morbidity and mortality rates related to treatment, regardless of whether the treatment is surgical or endovascular. However, this grim prognosis is based on results that indiscriminately group all blister aneurysms together without taking into account the heterogeneous appearance of these lesions. The goal of this study was 2-fold: to determine whether different blister aneurysm morphologies present different pitfalls, which would then require different surgical strategies, as well as to determine whether there are identifiable subgroups of these types of aneurysms based on morphology.

METHODS

The authors reviewed the charts, cerebral catheter angiograms, surgical reports, and intraoperative videos of all ICA blister aneurysms treated surgically at the Centre Hospitalier de l'Université de Montréal from 2005 to 2012 to investigate whether there was a relationship between morphology and pitfalls, and whether different surgical strategies had been used according to these pitfalls. During this review process the authors noted 4 distinct morphological aspects. These 4 aspects led to a review of the English and French literature on blister aneurysms in which imaging was available, to determine whether other cases could also be classified into the same 4 subgroups based on these morphological aspects.

RESULTS

The retrospective review of the authors' series of 10 patients allowed a division into 4 distinct subtypes: Type I (classic), Type II (berry-like), Type III (longitudinal), and Type IV (circumferential). These subtypes may at times be progressive stages in the arterial anomaly, and could represent a continuum. Each subtype described in this paper presented its own pitfalls and required specific surgical adaptations. Upon reviewing the literature the authors retained 35 studies involving a total of 61 cases of blister aneurysms, and all cases were able to be classified into 1 of these 4 distinct subtypes.

CONCLUSIONS

Although they share some common characteristics, blister aneurysms may be divided into distinct subtypes, suggestive of a continuum. Such a classification with a detailed description of each type of blister aneurysm would allow for better recognition to anticipate complications during intervention and better assess the different treatment strategies according to the subtypes.

Sole stenting with large cell stents for very small ruptured intracranial aneurysms

A flow-diverting stent such as the Pipeline embolization device (PED, ev3 Endovascular, Plymouth, MN, USA) and Silk flow-diverting stent (Balt Extrusion, Montmorency, France) offers an acceptable alternative for the treatment of difficult aneurysms according to their morphologies, including giant, wide-necked, fusiform, and blister types. However, complications arising from the use of these stents have frequently been reported including several cases of branch artery occlusion and delayed occlusion of the stented parent vessel shortly after antiplatelet medications were discontinued, highlighting the potential need for long-term antiplatelet therapy, and disastrous bleeding complications in unruptured aneurysm. In addition, these microcell stents are difficult to use in distal aneurysms located over the ICA bifurcation and basilar tip because of the stiffness of the device, and perforating vessel occlusion is more likely to occur due to the characteristics of the stent. Before the era of flow-diverting microcell stents, large cell intracranial stents like the Neuroform stent (Boston Scientific/Target Therapeutic, Fremont, CA, USA) and Enterprise stent (Cordis Neurovascular, Miami, FL, USA) without coiling were used to provide flow-diverting effects for complex intracranial aneurysms. Sole stenting has been used even in cases of ruptured aneurysm, with patients on different antiplatelet medications. However, no single endovascular institute has embraced sole stenting using large cell intracranial stents as a systemized treatment for ruptured intracranial aneurysms. Here we designed this study to evaluate the possibility of safely treating very small aneurysms using one or two stents without coiling during the period of subarachnoid hemorrhage (SAH). This retrospective study was conducted with eight patients who had rupture of very small intracranial aneurysms (less than 3 mm in size). All were treated using the Neuroform and the Enterprise stents; there was single stenting in five, in-stent telescopic stenting in two, and Y-configured stenting in one. The angiographic results with clinical outcomes were collected and analyzed. Complete aneurysm obliteration was observed in three cases, and size reduction or stable angiographic findings was found in five cases on the last follow-up angiography. No growing aneurysm or rebleeding was found on any follow-up angiography. Thromboembolic complications were found in one patient. It is difficult to make conclusions on the long-term efficacy of this technique with such a small number of cases, however sole stenting with a large cell intracranial stent for the treatment of very small aneurysms may be used safely as an alternative treatment even during an episode of SAH.