Case Report:

Background: Carotid artery occlusion, whether therapeutic, iatrogenic, atherosclerotic, or congenital, induces profound hemodynamic changes in the cerebral circulation. Collateral channels within the circle of Willis compensate to maintain cerebral perfusion; however, the resulting increases in flow velocity, wall shear stress, and pressure gradients are believed to ultimately contribute to aneurysm formation. While Case description: A 27-year-old male with severe headache was found to have a partially thrombosed giant serpentine aneurysm (GSA) of the left M2 inferior trunk. The patient underwent double-barrel superficial temporal artery-middle cerebral artery (STA-MCA) bypass followed by proximal clipping. Postoperative imaging confirmed complete exclusion of the aneurysm and excellent bypass patency. Three months later, acute aphasia and right hemiparesis developed. Angiography revealed two newly formed aneurysms along the left MCA bifurcation point and the M2 superior trunk, which were successfully treated with endovascular coil embolization and parent artery occlusion. At nine-month follow-up, the patient remained neurologically intact with patent bypass grafts and no aneurysm recurrence. Conclusions: This case illustrates an unusual pattern of early, multiple, non-anastomotic