Abdominal aortic aneurysms are relatively common within those aged over fifty, with an incidence of between 1% and 4%. The risk of rupture of an aortic aneurysm
is approximately 1% per year of aneurysm; aortocaval fistula is a rare form of rupture, accounting for 0.3-4% of ruptures, from the aorta to the IVC. Patients are often in high cardiac failure at presentation (50%) with about 20% having the classic triad of abdominal or back pain with a palpable aortic aneurysm and a continuous abdominal bruit. Additionally, due either to reduced renal perfusion or increased renal venous pressure, they can be in acute renal failure.
On CT the presence of early IVC enhancement suggests an aortocaval fistula and with helical scanning the fistula can often be visualised. Preoperative diagnosis of aortocaval fistula reduces the degree of intraoperative haemorrhage.
Complications of aortocaval fistula include pulmonary embolism of the aneurysmal debris, and failure to diagnose preoperatively due to a thrombosed fistula tract.
The differential diagnosis for early IVC enhancement includes: right heart failure, carcinoid syndrome, superior vena cava obstruction, aortocaval fistula and vascular injury.