Anastomotic pseudoaneurysm presenting 50 years after common carotid artery-subclavian artery bypass: illustrative case.

backgroundCommon carotid artery (CCA)-subclavian artery bypass is performed for CCA occlusive disease. Reported complications include infection, occlusion, anastomotic leakage, and nerve injury. A pseudoaneurysm at the anastomotic site is rare, and most develop within 1-2 years after the procedure. The authors present a case of an anastomotic pseudoaneurysm occurring 50 years after bypass surgery. OBSERVATIONS: A 76-year-old woman presented with progressive neck swelling. She had undergone left CCA-subclavian artery bypass 50 years earlier. Imaging revealed a pseudoaneurysm, with occlusion of both the left CCA and the graft. The distal CCA was opacified via retrograde flow through an extracranial-intracranial anastomosis from the right internal carotid artery (ICA). The aneurysm was thought to be supplied solely by this. Ligation of the ICA-external carotid artery bifurcation was planned. Intraoperatively, however, several microvessels resembling the vasa vasorum were found entering and supplying the pseudoaneurysm. Trapping and excision were achieved by dividing them. Pathological analysis showed a fibrous aneurysm wall containing remnants of the vascular prosthesis, with immune cell infiltration, phagocytosis, and surrounding microvessels. LESSONS: Anastomotic pseudoaneurysm may occur decades after CCA-subclavian artery bypass. This case underscores that prosthetic grafts require lifelong surveillance, as delayed complications may result from long-term graft degeneration, chronic inflammation, or occult infection. https://thejns.org/doi/10.3171/CASE25704.