Peri-Aneurysmal Contact as a Risk Factor for Aneurysmal Rupture in Unruptured Intracranial Aneurysms: An Overview

The occurrence and growth of unruptured intracranial aneurysms are believed to be influenced by intraluminal factors of blood flow dynamics and pathological factors of the aneurysm wall. In addition to these, the deformation and rupture of aneurysms require consideration of physical extra-luminal factors due to contact between the aneurysm and surrounding structures including brain parenchyma, cranial nerves, arteries, veins, cranial base bone and dura mater. The extra-luminal factors of aneurysms were evaluated based on the presence of peri-aneurysmal contact. Peri-aneurysmal contact, depending on the type, location, and size of aneurysms, influenced the growth pattern of the aneurysm. Recently, with the imaging of magnetic resonance cisternography, it had become possible to non-invasively assess the anatomical relationship between the outer wall of aneurysms and the surrounding structures. Fusion images overlaying 3D magnetic resonance cisternography with 3D computed tomography angiography or 3D magnetic resonance angiography detailed the anatomical relationship of peri-aneurysmal contact, position of contact sites, and depth. We depicted the anatomical construction of peri-aneurysmal contact and bleb in unruptured intracranial aneurysms using fusion images and studied the intraluminal blood flow dynamics using computational fluid dynamics. As a result, peri-aneurysmal contact was observed to be involved as an independent variable in the process of bleb formation. It was suggested that factors extra-luminal to the aneurysm, such as peri-aneurysmal contact, might have a greater impact on bleb formation than intraluminal factors like blood flow dynamics. Peri-aneurysmal contact emerged as a noteworthy extra-luminal factor, particularly associated with bleb formation, presenting a substantial risk of rupture in unruptured intracranial aneurysms. These findings underscore the importance of considering the presence and extent of peri-aneurysmal contact alongside intraluminal and wall-related factors in future evaluations. The implications of this overview extend to the development of risk assessment protocols, providing valuable insights for guiding early intervention strategies and ultimately contributing to improved patient outcomes.