Perianeurysmal cyst formation in the brainstem after coil embolization: illustrative case

BACKGROUND Perianeurysmal cysts in the brainstem after endovascular coil embolization are rare, and their underlying mechanism remains unclear. The authors reported a case of a postcoiling perianeurysmal cyst that developed 6 years after endovascular coil embolization for a ruptured aneurysm and reviewed the related literature. OBSERVATIONS A 77-year-old woman had a history of subarachnoid hemorrhage 6 years earlier. The ruptured large left vertebral artery–posterior inferior cerebellar artery aneurysm was treated with endovascular coil embolization. Two years later, the aneurysm regrew and perianeurysmal brainstem edema was detected on magnetic resonance imaging (MRI); stent-assisted coil embolization combined with low-flow bypass was performed. Follow-up MRI showed that the perianeurysmal edema gradually transformed into a perianeurysmal cyst over the next 3 years. Finally, the perianeurysmal cyst caused gait disturbance with ataxia, and the patient received cyst puncture. After surgery, the symptom was immediately improved. LESSONS The authors reported, for the first time, postcoiling of perianeurysmal cyst formation treated by cyst puncture. If perianeurysmal edema is detected after endovascular coil embolization, especially for large aneurysms, it is necessary to consider progression to cyst formation and follow up over time. In addition, cyst puncture is effective, depending on the symptoms and the lesion.