Silent Rupture: Atypical Presentation of Aorto-Caval Fistula Secondary to Giant Abdominal Aortic Aneurysm.

Abdominal aortic aneurysm (AAA) is a potentially life-threatening condition characterized by abnormal dilation of the abdominal aorta, typically due to chronic arterial wall degeneration. Aorto-caval fistula (ACF) is a rare but serious complication of AAA, occurring in less than 1% of cases overall, with incidence increasing in the setting of rupture. ACF involves the formation of an abnormal communication between the abdominal aorta and the inferior vena cava (IVC), resulting in blood shunting from the arterial to the venous system. This can cause reduced organ perfusion, high-output cardiac failure, and multiorgan dysfunction. We present the case of a 65-year-old hypertensive male with a known AAA who presented with 2 days of abdominal pain but no systemic or gastrointestinal symptoms. Physical examination revealed periumbilical tenderness, while laboratory results were normal. Contrast-enhanced computed tomography of the abdomen revealed a large (10 cm) infrarenal AAA with evidence of rupture, mural thrombus, and a fistulous connection to the IVC. The patient underwent successful endovascular repair with complete resolution of the aneurysm and fistula, as shown in follow-up imaging. This case highlights the importance of high clinical suspicion and the role of early imaging in diagnosing ACFs, even in the absence of classical signs or lab abnormalities. The aim is to raise awareness of such atypical presentations and emphasize our case's uniqueness in its silent, stable, yet severe presentation.