Hemodynamic Evaluation of Residual Cavity Growth in a Basilar-Tip Cerebral Aneurysm Post-coiling Using Silent Magnetic Resonance Angiography (MRA): A Case Report

Coil embolization of cerebral aneurysms often encounters challenges in achieving complete filling of the aneurysm sac due to complex shapes and hemodynamic factors, frequently resulting in the formation of a residual cavity (RC) at the aneurysm neck. The hemodynamic mechanisms underlying RC formation and growth, however, remain poorly understood. Computational fluid dynamics (CFD) analysis, combined with silent MRA free from contrast agents and metal artifacts, offers a promising approach to elucidate these mechanisms, potentially enhancing the clinical management of cerebral aneurysms post-coiling. Herein, we report a case of a basilar-tip aneurysm treated with coil embolization, where sequential silent MRA and CFD analysis were employed to investigate hemodynamic factors driving rapid RC growth. Initial RC formation was attributed to coil compaction driven by flow impingement at the aneurysm neck onto the neo-endothelial surface, contributing to vertical growth. In contrast, secondary flows detached from the main inflow jet were observed in distal regions of the RC, leading to flow stagnation, wall vulnerability, and subsequent horizontal expansion of the aneurysmal wall. This case highlights the role of secondary detached flows in RC enlargement, emphasizing their potential to weaken the aneurysm wall and drive sac expansion. CFD analysis using silent MRA is a valuable tool for understanding RC hemodynamics and post-coiling management for cerebral aneurysms.