Straight border sign of the liver: spectrum of CT appearances and causes

Attenuation differences bordered by straight lines within the liver (the straight border sign) are sometimes seen at computed tomography (CT). This phenomenon, which was demonstrated with unenhanced CT over a dozen years ago, does not represent a hepatic mass and is often associated with vascular compromise. Major causes of the straight border sign include fatty liver, confluent fibrosis, radiation hepatitis, and vascular abnormalities such as tumor thrombus, thromboembolus, compression, and arterioportal shunt. The frequency of this finding increases when intense contrast enhancement is used, especially when contrast material is administered via the superior mesenteric artery (CT during arterial portography) or hepatic artery (CT arteriography). The use of spiral CT is apparently increasing the chances of encountering this sign in daily practice. To correctly interpret the straight border sign, one should consider the distribution (anatomic vs nonanatomic), the attenuation (low vs high), and the use and technique of contrast enhancement.