New Strategy for Flow Outlet Creation to Prevent Ischemic Complications Involving Perforating Arteries when Treating an Unruptured Large Aneurysm

When treating an unruptured large aneurysm (AN) that is not suitable for simple clipping, proximal occlusion of the parent artery with revascularization is common practice. However, a thrombus might develop in the blind alley after occlusion of the parent artery due to stagnation of blood flow, and ischemia involving perforators can develop despite antithrombotic therapy. Therefore, we tried to create flow outlets at the blind alley in two cases. The first case was a 68-year-old-man with a regrowing basilar artery-superior cerebellar artery aneurysm (BA-SCA AN) after coil embolization. Superficial temporary artery (STA)-SCA bypass, STA-posterior cerebral artery (PCA) bypass, and proximal occlusion (PO) of the BA were performed. The BA and associated perforators were not visualized with intraoperative indocyanine green angiography. We then performed transposition of the SCA into the blind alley as a flow outlet for stagnant blood. During occlusion of the BA and perforating arteries, motor evoked potentials (MEPs) transiently disappeared, but recovered to 70% of preocclusion levels after removal of temporary clips. Thrombosis of the BA was prevented, but ischemic complications subsequently developed in perforators. The second case was a 72-year-old man with a fusiform AN of the middle cerebral artery (MCA). After STA-M2 bypass, STA-anterior temporal artery (ATA) bypass from the AN, and PO of the MCA were performed. Perforators arising from the distal AN were thought to be at risk of ischemia based on intraoperative MEPs; therefore, the proximal ATA was not occluded to preserve a flow outlet from the AN. Delicate pressure balance resulted in indolent thrombosis of the AN without causing ischemic complications. The AN was not apparent two weeks later, and has still not recurred after 33 months of follow-up. Creation of a flow outlet in a deep and narrow space is difficult. Moreover, delayed postoperative ischemia involving perforators is not always predictable. Even with use of intraoperative monitoring, careful planning is required.