OBJECTIVE Our goal was to describe attenuation differences bordered by a straight line in the right hepatic lobe on enhanced CT in patients with right adrenal tumors and to discuss the cause of this appearance. MATERIALS AND METHODS Three patients showing attenuation differences bordered by a straight line were discovered in the CT files of 26 cases of right adrenal tumor over 3 cm in diameter. All CT scans were examined by incremental dynamic study. RESULTS Two patients had large zone of hyperattenuation in the right lobe bordered with a straight line intersecting both anterior branches of the right portal vein and the inferior vena cava (IVC). A third patient and one of the two patients mentioned already had zones of relative hyper- and hypoattenuation in the medial portion of the posterior hepatic segment, respectively. All three patients had large right adrenal tumors, which severely compressed the right hepatic vein near its confluence with the IVC and/or the IVC in or below its intrahepatic portion. The distribution of attenuation differences was similar to the hyperattenuation at CT arteriography or perfusion defect at CT arterial portography under temporary balloon occlusion of the right hepatic vein and inferior right hepatic vein, respectively. CONCLUSION Straight-bordered attenuation differences within the right hepatic lobe at dynamic CT can be caused by compression of the right hepatic vein by large right adrenal tumors.