Hemodynamic remnant drift after coil embolization: longitudinal silent MRA and computational fluid dynamics analysis of a migratory neck remnant. Illustrative case.

backgroundNeck remnants after coil embolization are usually attributed to coil compaction or aneurysm regrowth, but their longitudinal spatial behavior has rarely been examined. OBSERVATIONS: The authors report an unruptured posterior communicating artery aneurysm treated with coil embolization, followed by serial silent MR angiography (MRA) and computational fluid dynamics (CFD). Fusion imaging from an intradome perspective showed progressive migration of a small residual cavity, rather than concentric enlargement, along the aneurysm neck plane at 6, 12, and 18 months. CFD demonstrated that remnant location corresponded to temporal changes in inflow targeting, best reflected by the flow rate ratio, whereas wall shear stress magnitude alone did not correlate consistently with remnant evolution. Directional WSS patterns and streamlines suggested shifting hemodynamic guidance of the residual cavity. The authors term this phenomenon a "migratory neck remnant" or "remnant drift." LESSONS: Serial silent MRA combined with CFD can visualize longitudinal migration of neck remnants. Hemodynamic inflow targeting appears to determine remnant location, whereas blood pressure-related wall stress may govern long-term stability. Recognition of remnant drift may improve prediction of aneurysm recurrence and guide surveillance strategies. https://thejns.org/doi/10.3171/CASE26109.