A Case of Bilateral Giant Internal Carotid Artery Aneurysms at the Cavernous Portion Managed by 2-stage Extracranial–Intracranial Bypass with Parent Artery Occlusion: Consideration for Bypass Selection and Timing of Surgeries

Bilateral giant internal carotid artery (ICA) aneurysms at the cavernous portion with bilateral cranial nerve symptoms are extremely rare. Extracranial–intracranial (EC-IC) bypass with parent artery occlusion (PAO) is one of the preferred procedures for giant ICA aneurysm at the cavernous portion with cranial nerve palsy; however, optimal bypass selection and the timing of surgery are controversial, particularly in bilateral cases. A 28-year-old woman developed left third nerve palsy with giant ICA aneurysms at the bilateral cavernous portion. Because only the left aneurysm was symptomatic, she initially underwent left EC-IC bypass using a saphenous vein graft with PAO without complications, which relieved her symptoms. However, she developed right third/fifth nerve palsy 10 months later, at which time magnetic resonance (MR) imaging and MR angiography revealed an enlarged right ICA aneurysm and shrunken left ICA aneurysm. Balloon test occlusion of the right ICA identified sufficient ischemic tolerance; therefore, she underwent right superficial temporal artery–middle cerebral artery bypass with PAO. Both bypasses were confirmed by MR angiography to be patent after surgery. Cranial nerve palsy gradually improved postoperatively, and single-photon emission computed tomography confirmed static cerebral hemodynamics. In conclusion, high-flow EC-IC bypass with PAO is recommended in the first stage of surgery on a unilaterally symptomatic side to minimize postoperative hemodynamic stress to the contralateral aneurysm. Once the contralateral side becomes symptomatic, second stage EC-IC bypass with PAO, either low-flow or high-flow bypass, is recommended based on the results of balloon test occlusion.