Distal outflow occlusion with bypass revascularization: last resort measure in managing complex MCA and PICA aneurysms

Partial trapping with or without bypass revascularization is a well-established strategy in the surgical management of complex aneurysms. Distal outflow occlusion is performed by occluding the efferent artery downstream of the aneurysm and represents an alternative to proximal inflow occlusion in partial trapping treatment. With this article we report a case series employing distal outflow occlusion for managing posterior-inferior cerebellar artery (PICA) and middle cerebral artery (MCA) complex aneurysms and discuss the rationale of this treatment strategy. A case series of eight patients who underwent surgery for complex PICA (n = 3) and MCA (n = 5) aneurysms by means of distal outflow occlusion and flow-replacement bypass is presented. Two out of the eight patients presented with subarachnoid hemorrhage (SAH) (1 PICA and 1 MCA aneurysm). In seven out of eight patients (87.5 %), total aneurysmal thrombosis was obtained; in one patient, postoperative neuroimaging showed a partial aneurysmal thrombosis. Aneurysm growth or delayed rupture was not observed. All the bypasses were patent at the end of the procedure and all but one at follow-up (asymptomatic occlusion). One patient had postoperative worsening, unrelated to bypass patency. All other patients improved. Three patients maintained an mRS score of 1, four patients had improved mRS scores by a parts per thousand yen1, and 1 patient had a worsened mRS score compared to preoperatively. We believe that partial trapping with distal outflow occlusion for treating complex intracranial aneurysms represents a useful strategy as a last resort measure. To avoid cerebral ischemia, flow-replacement bypass is key to success.