Enlargement of a Middle Cerebral Artery Aneurysm after Intra-Aneurysmal Embolization with Parent Artery Preservation for an Ipsilateral Large Internal Carotid Artery Aneurysm: A Case Report.

We report a 77-year-old woman with marked enlargement of a middle cerebral artery (MCA) aneurysm 4 years after the successful intra-aneurysmal embolization of an ipsilateral large internal carotid artery (ICA) aneurysm. She intially presented with right third cranial nerve palsy due to a large ICA aneurysm, 20.8 mm in diameter. Initial magnetic resonance angiography (MRA) revealed a signal decrease in the right MCA, suggesting hemodynamic disturbance based on the contrast pooling in the right large ICA aneurysm exhibiting “Windkessel phenomenon”. The large ICA aneurysm was successfully managed by intra-aneurysmal embolization with parent artery preservation, and immediate post-treatment MRA demonstrated significant signal recovery in the right MCA. Meticulous follow-up by MRA identified sudden growth in the aneurysmal height within 1 week after embolization, with further growth over the following 4 years, necessitating microsurgical clipping. Enlargement of the ipsilateral distal aneurysm following the treatment of proximal large aneurysm could be altered by marked distal hemodynamic change in view of the sudden amelioration of the “Windkessel phenomenon”. Thus, we recommend meticulous follow-up of the associated distal aneurysm after the management of proximal large or giant aneurysms with parent artery preservation.