gms | German Medical Science

Objective: Anatomical variations of distal basilar artery are common findings during diagnostic of cerebral circulation and are mostly interpreted as benign conditions. The goal of this study was to investigate if these alternative patterns are related to the formation and rupture of aneurysms in this location.

Methods: In a retrospective study we analyzed 95 patients with 101 aneurysms located on distal basilar artery, who were treated in our department between January 2000 and February 2017. The aneurysms of the basilar tip, of the precommunicating segment of the posterior cerebral artery (P1) and of the anterior pontomesencephalic segment of the superior cerebellar artery (s1), that share common embryological origin, were considered for the study. The presence of an incomplete fusion of the distal basilar artery, of a fetal posterior communicating artery and of an immature P1-P2A junction was identified on imaging records of the patients. The prevalence of these patterns in the above mentioned population was compared to a control group of 68 patients with aneurysms in other portions of the intracranial circulation.

Results: An immature P1-P2A junction was encountered in all 5 patients with P1 aneurysm, resulting in a statistically relevant correlation (P= 0.015). The reason for this relation is unknown and can not be deduced from the hemodynamic theories of aneurysms formation. A positive correlation was encountered between the presence of basilar tip or s1 aneurysms and an immature P1-P2A junction. An immature fusion pattern of the distal basilar artery was also more common in all three subgroups of aneurysms compared to the control population. Probably due to the limited sample size these results did not reach statistical significance. A correlation between the presence of a fetal posterior communicating artery and the presence of an aneurysm in the distal basilar artery could be excluded.

Conclusion: The presence of an immature P1-P2A junction should be considered as a risk factor for aneurysms of the P1 segment. Reasons may lie in the structure of the wall of this embryological immature arterial segment. Multicenter trials are required to collect a bigger patient’s cohort to confirm the role of an immature P1-P2A junction in the pathogenesis of s1 and basilar tip aneurysms and the impact of immature fusion patterns of the distal basilar artery in the pathogenesis of all three aneurysm locations considered in this study.