Case report: persistent fifth aortic arch presenting as a giant ascending aortic aneurysm: diagnostic challenge and surgical resolution with Bentall procedure.

Background: An ascending aortic aneurysm is defined as dilatation of the ascending aorta to ≥1.5 times its normal diameter. Surgical intervention is recommended when the diameter exceeds 55 mm to prevent life-threatening complications such as rupture or dissection. Persistent fifth aortic arch is a rare congenital vascular anomaly, which may present as a dual-lumen aortic configuration and can mimic acquired pathological conditions such as aortic dissection or aneurysm, posing a diagnostic challenge. Case summary: A 39-year-old male with long-standing hypertension presented with cough and shortness of breath. Initial computed tomography (CT) performed to exclude pulmonary embolism incidentally revealed a markedly dilated ascending aorta. Following intensive care unit admission and stabilization, echocardiography and CT aortography demonstrated severe aortic regurgitation and a giant ascending aortic aneurysm measuring 10.5 cm with dual-lumen morphology interpreted radiologically as Stanford type A aortic dissection. The patient underwent urgent Bentall procedure. Histopathological examination confirmed a dual-lumen vascular structure consistent with persistent fifth aortic arch, establishing the congenital aetiology. The patient recovered uneventfully and remained asymptomatic during cardiothoracic follow-up. Conclusion: This case highlights the diagnostic challenge of distinguishing congenital persistent fifth aortic arch from acquired aortic dissection in the setting of a giant ascending aneurysm. Despite radiologic ambiguity, prompt surgical repair was definitive. Histopathological confirmation provided etiologic clarity and contributes to understanding the natural history of this rare anomaly.