Straight line sign: appearance and significance during CT portography.

The computed tomographic (CT) angiograms of 44 patients who were being evaluated for possible hepatic surgery were studied. All patients were imaged with CT arterial portography (CTAP), delayed CT of the liver, and magnetic resonance (MR) imaging. All CTAP studies were evaluated for a "straight line," a linear variation in contrast within the liver. Sixteen patients (36%) demonstrated the straight line sign. All 16 had a mass at the proximal portion of the defect. Nine of 16 had defects that clearly correlated with portal venous distribution seen at limited digital angiography. Fourteen of the 16 patients showed loss of the straight line sign at delayed CT and/or MR imaging of the liver. These defects are thought to be due to vascular obstruction. The straight line sign will probably be seen more frequently as CTAP is more commonly used. Recognition of the sign is important in the evaluation of primary liver carcinomas, since it signifies that the tumor may be inoperable. Also, if metastatic disease is present, it alerts the surgeon to the proximity of the portal vein to the neoplasm.