Editorial: Peculiarities of unruptured internal carotid artery bifurcation aneurysms

Internal carotid artery bifurcation aneurysms are infrequent. Therefore, in most of the large prospective observational studies these aneurysms are usually underrepresented, and there is generally scarce information about the natural history and the outcome of this very challenging pathology. As for other intracranial aneurysms, the risk of aneurysmal rupture without intervention should be weighed against the risk of microsurgical clipping or endovascular treatment. In case of internal carotid artery bifurcation aneurysms, the published data are occasional and not conclusive.

In this superb study, La Pira et al. present a prospectively collected and retrospectively analyzed cohort of unruptured internal carotid artery bifurcation aneurysms providing an original snapshot of the current treatment paradigm and overall results, with a clinical followup of 42.8 months. The conclusions are very significant for the neurosurgical community to establish a treatment algorithm considering the newer available endovascular procedural and diagnostic endovascular techniques.

As is well known, the internal carotid artery bifurcation aneurysms represent a challenge for both endovascular and microsurgical treatment. The presence of important perforating vessels, sometime like a basket over the aneurysmal dome, and the very high allocation in the circle of Willis demonstrate the need for personalized solutions.

The incidence in the authors’ single institution was 61 patients of 1253 patients with unruptured intracranial aneurysms. The 5 % incidence of subjects with internal carotid artery bifurcation aneurysms was accompanied by the evidence of a significantly younger age and a higher rate of smoking and aneurysm multiplicity. Moreover, the overall outcomes were very good for all treatment modalities, without mortality or permanent severe disability. Nevertheless, the cohort treated by microsurgery presented better results than the endovascular cohort, with a higher aneurysm occlusion rate (100 % vs. 60 %) and minor recurrence rate. This observation should be considered with caution and further followed.

In the presence of a contralateral ICA occlusion, the authors also suggest the treatment of very small aneurysms. This point is still controversial, because the vulnerability due to mechanical treatment and/or vasospasm may allow a functional occlusion of the only working carotid artery. Additional diagnostic data about the shape and hemodynamics of the aneurysmal flow will help in the decision-making process.

Overall, through this well-written, thoughtfully constructed manuscript, the authors deliver a meaningful contribution to the literature in the challenging field of unruptured internal carotid artery bifurcation aneurysms. This new previously unpublished information is obtained in a large series and provides new perspectives in the neurovascular field. The conclusions corroborate our personal clinical experience in the field and encourage cerebrovascular neurosurgeons and neuroradiologists to approach unruptured internal carotid artery bifurcation aneurysms with the following arguments:

• 1. The treatment of unruptured internal carotid artery bifurcation aneurysms is safe and effective.

• 2. The treatment procedures in younger patients or patients with known risk factors for aneurym rupture (i.e. smoking, familiarity, hypertension, and aneurysm multiplicity) is strongly recommended.

• 3. In the presence of very small aneurysms (<3 mm), conservative treatment should be considered.

• 4. Endovascular treatment leads to a high rate of incomplete occlusions. However, no SAH was observed in the follow-up period.

• 5. Microsurgical clipping remains a valuable treatment option particularly for younger patients.

• 6. Newer endovascular tools such as flow diverters have improved the treatment options.

An interesting point for further research in the field will be the assessment of the aneurysmal internal flow characteristics and the morphological irregularity of the aneurysmal wall (i.e., the presence of a daughter sac, a bottleneck shape, etc.) and other diagnostic tools in order to identify further risk factors and select the cohort that needs a treatment more objectively.