A Case of a Perianeurysmal Cyst Following Stent-Assisted Coil Embolization of an Unruptured Vertebral Artery Aneurysm

Objective: To report the rare case of a patient with a perianeurysmal cyst following stent-assisted coil embolization of an unruptured vertebral artery aneurysm. Case Presentation: A 63-year-old woman underwent stent-assisted coil embolization for an unruptured vertebral artery aneurysm embedded in the brainstem (pons). Complete occlusion of the aneurysm was successfully achieved. However, subsequent magnetic resonance imaging (MRI) conducted 8 months after the procedure showed perilesional edematous changes surrounding the aneurysm, and at 20 months, cyst formation was observed in the vicinity of the aneurysm. Progressive enlargement of the cyst eventually led to the development of paralysis and dysphagia, necessitating cyst fenestration surgery. Although postoperative reduction in the cyst size was achieved, the patient experienced complications in the form of aspiration pneumonia and bacterial meningitis, which resulted in a life-threatening condition. Conclusion: Aneurysms embedded in the brain parenchyma should be carefully followed up, recognizing the risk of perianeurysmal cyst formation after coil embolization.