The authors report the magnetic resonance (MR) and computed tomography (CT) features of what is believed to be thrombophlebitis of the left cava of a duplicated IVC, which mimicked lymphadenopathy, and prompted both a CT-guided needle aspiration biopsy and surgical exploration. Knowledge that retroperitoneal vascular anomalies can mimick lymphadenopathy, both clinically and radiographically, may help obviate further testing and intervention.