Rapid Development of an Aneurysm at the Anastomotic Site of a Superficial Temporal Artery to Middle Cerebral Artery Bypass: Case Report and Literature Review

Background: Direct extracranial to intracranial (EC-IC) bypass is a valuable treatment option for symptomatic occlusive cerebrovascular disease and complex intracranial aneurysms. Aneurysm formation at or near the anastomotic site is a rarely reported phenomenon, and the pathophysiology and appropriate management of such de novo aneurysms are not clear. Case Description: Here we present the case of a superficial temporal to middle cerebral artery (STA-MCA) anastomosis that was complicated by aneurysm formation at the anastomotic site. This was treated with microsurgical clipping with preservation of the bypass. Pathologic analysis of the lesion was consistent with a pseudoaneurysm. We provide a literature review of this phenomenon, which is most often associated with low-flow STA-MCA bypasses, including review of the pathologic findings associated with it. Conclusion: Pseudoaneurysm formation at the site of an EC-IC bypass is a rare phenomenon that should be recognized and treated to prevent further growth and rupture.