Anastomotic Aneurysm Formation after High Flow Bypass Surgery: A Case Report with Histopathological Study

Bypass surgery is often used in the treatment of large and giant aneurysms. Major complications that often arise during the perioperative period include cranial nerve palsy, ischemic complications, and hyperperfusion. However, there have been a few reports about late onset complications such as anastomotic aneurysms. In particular, anastomotic aneurysm after high flow bypasses has never been reported. A 57-year-old woman who had been suffering from left eye pain was diagnosed with a large aneurysm of the left internal carotid artery (ICA) in the cavernous portion. She was treated with high flow bypass surgery using radial artery graft and proximal ICA ligation. One and a half year after surgery, a de novo aneurysm (7.5 mm in maximum diameter) was detected in the anastomotic site. To prevent rupture, the aneurysm was resected and the middle cerebral artery (MCA) was reconstructed via superficial temporal artery (STA)-MCA bypass. Postoperative course was uneventful and the anastomotic aneurysm did not recur until 2 years after second surgery. Histological evaluation of the anastomotic aneurysm demonstrated loss of smooth muscle cells and proliferation of neointima, features consistent with a true aneurysm. Interestingly, the above changes were prominent in the radial artery graft while the MCA was almost histologically intact. As such, intraoperative intimal damage and postoperative hemodynamic stress to the radial artery graft may be a cause of aneurysm formation. Anastomotic aneurysm may occur after high flow bypass, necessitating careful postoperative follow-up.