A Rare Case of Enlarged Dissecting Aneurysm Occurring One Year After Conservative Management of Azygos Anterior Cerebral Artery Dissection.

Anterior cerebral artery (ACA) dissection is generally managed with conservative treatment, often resulting in a favorable prognosis. However, cases with delayed enlargement of dissecting aneurysms following conservative therapy are rare. We describe a 46-year-old male patient who presented with concurrent subarachnoid hemorrhage and cerebral infarction caused by ACA dissection. Initial digital subtraction angiography (DSA) revealed an azygos ACA, as well as dilation and stenosis in the A2 segment. Follow-up DSA on the sixth and fifteenth days detected dissecting aneurysms at the bifurcation of the left pericallosal artery and at the peripheral bifurcation of the middle internal frontal artery, with intervening stenosis. The patient recovered well without rebleeding after conservative management. However, one year later, magnetic resonance imaging (MRI) indicated an enlargement of the aneurysm. Simple coil embolization was performed, and a 6-month postoperative MRI confirmed the disappearance of the aneurysm. This case suggests that while conservative management of azygos ACA dissections can be effective, careful and long-term follow-up is crucial due to the potential for delayed aneurysm formation.