Introduction Cerebrovascular diseases are a growing social and clinical problem, and their pathogenesis is currently being thoroughly investigated. The intravascular anatomy of the cerebral circulation remains poorly understood, although an increasing number of endovascular interventions are being conducted during the course of diagnosis and treatment. The purpose of this study was to describe intravascular structures in the vertebrobasilar system and to investigate the hemodynamic consequences of their presence.

Methods Thirty anatomical specimens of the human brain were analyzed via angioscopy of the vertebrobasilar system, and the presence of intravascular structures was documented. Additional histological studies were performed. The effect on blood flow was simulated using computational fluid dynamics by studying 5 different cases.

Results In 8 cases (26.7%), the following endovascular structures were visualized: 6 strings, one septum, and one chord. The histological structure showed a layered pattern, resembling that of the arterial wall: the outermost tunica intima, the innermost adventitia and the tunica media in between. Blood flow simulations revealed several areas of disturbed flow, including areas of low wall shear stress and recirculations, as well as areas of elevated wall shear stress.

Conclusions Intravascular structures are common in the basilar artery. The reason for their formation is the incomplete fusion of the longitudinal neural arteries, and together with fenestrations, they belong to the basilar nonfusion spectrum. The presence of structures can cause technical difficulties and ischemic complications related to endovascular interventions. Hemodynamic changes caused by endovascular structures can promote atherosclerosis, thromboembolism, narrowing of the pontine arteries and the development of aneurysms.

The authors have declared no competing interest.

The study was funded by the National Science Centre, Poland (award number 2020/37/B/ST8/03430). The National Science Center had no involvement in the study design, in the collection, analysis and interpretation of data, in the writing of the article, or in the decision to submit the article for publication The numerical analyses were performed with the support of the Interdisciplinary Center for Mathematical and Computational Modeling (ICM) of the University of Warsaw, Poland under grant no G97-1935 and with the support of the ANSYS National License.

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