Duodenocaval fistula (DCF) is an uncommon but lethal clinical entity. The high mortality has been attributed to the difficulty of diagnosis before attempts at definitive therapy. In this case report, we describe a patient with a series of computed tomography (CT) examinations over a 2-mo period in hospital. A low-density air bubble appeared in the inferior vena cava (IVC) on the second day in hospital and became clear on day 19, and gradually enlarged. Magnetic resonance imaging (MRI) also clearly demonstrated a high-signal enteric contrast medium or thrombus and signal-void air bubbles in the IVC. However, cavography did not show the filling defect. We suggest that noninvasive CT and MRI should be chosen as a first-line investigation, and IVC, including the surrounding structures, should be carefully reviewed on images if DCF is clinically considered.