Background Coil migration is a complication of endovascular coiling of cerebral aneurysms that has not been well studied.

Objective To report the frequency, risk factors, management strategies, and outcomes of coil migration.

Methods This was a retrospective analysis of the clinical and radiological data of patients who underwent cerebral aneurysm coiling complicated by coil migration at five neuroendovascular centers in the United States, Canada, and France between 2008 and 2018.

Results Eighteen cases of coil migration met our study criteria with an occurrence of 0.3% (18/6071 cases) (procedural migration: 55%, delayed migration: 45%). The mean aneurysm maximal diameter, neck, and height to neck ratio in migration cases were 3.4±1.4 mm (range 2–7.6 mm), 2.4±0.9 mm (range 1.2–4.4 mm), and 1.4±0.4 (range 1–2.15), respectively. The 2 mm diameter coil was the most common (39%, range 1–2.5 mm) migrated coil. The length of the migrated coil was ≤4 cm in 95% of cases.

Patients managed conservatively (5/18, 28%) did well. Thromboembolic and/or hemorrhagic complications were noted in 6/10 migration patients treated by endovascular modalities and in all migration patients who underwent surgical treatment (4/4). Three deaths occurred (3/18, 17%) related to high Hunt and Hess grade subarachnoid hemorrhage.

Conclusion Coil migration is an uncommon but important complication of cerebral aneurysm coiling. Small aneurysms, aspect ratio <1.6, and small coils are significant risk factors. Endovascular treatment, such as using a stent retriever, can be considered for procedural, proximal migration, and/or in cases of vessel occlusion. Delayed or distal migration should be managed conservatively.