Contrast-enhanced ultrasound of benign liver lesions Jessica G. Zarzour, 1 Kristin K. Porter, 1 Hisham Tchelepi, 2 Michelle L. Robbin 1 1 Department of Radiology, University of Alabama at Birmingham, 619 19th Street South, JTN 338, Birmingham, AL 35294, USA 2 Department of Radiology, University of Southern California, Los Angeles, USA Abstract Liver lesions are often incidentally detected on ultrasound examination and may be incompletely characterized, requiring further imaging. Contrast-enhanced ultrasound (CEUS) was recently approved by the Food and Drug Administration in the United States for liver lesion char- acterization. CEUS has the ability to characterize focal liver lesions and has been shown to be superior to color Doppler and power Doppler ultrasound in the detection of tumor vascularity. Differentiating benign from malignant liver lesions is essential to characterizing liver lesions. The CEUS imaging characteristics of benign liver lesions are reviewed, including hepatic cysts, hemangiomas, focal fat, focal nodular hyperplasia, hepatocellular adenomas, ab- scesses, and traumatic lesions. Key words: Contrast-enhanced ultrasound—Liver lesions—Benign—FNH—Adenoma—Cyst— Abscess—Hemangioma Contrast-enhanced ultrasound (CEUS) has been used widely throughout European and Asian countries for many years and was recently approved by the Food and Drug Administration (FDA) in the United States for use in characterizing liver lesions. Focal liver lesions are commonly found during abdominal ultrasound exams either incidentally or in patients undergoing surveillance in chronic liver disease or cirrhosis. At times, benign liver lesions can be characterized by conventional gray scale and color Doppler if they have characteristic appear- ances of an anechoic cyst or a homogeneous hyperechoic hemangioma. However, often lesions that are detected on ultrasound examination are incompletely character- ized and require further imaging. CEUS has the ability to characterize focal liver lesions based on enhancement pattern. CEUS has been shown to be superior to color Doppler and power Doppler ultrasound in the detection of tumor vascularity [1]. In CEUS, the arterial phase starts within 10–20 s and persists for approximately 35–40 s after injection. The portal venous phase lasts for up to 2 min after injection and is characterized by homogeneous enhancement of the liver parenchyma [2]. The late phase persists through approxi- mately 5–6 min. Ultrasound contrast agents are smaller than the size of a red blood cell, and most are purely intravascular agents. As such, there is not a corresponding equilibrium or interstitial phase in CEUS to correlate with that seen on contrast-enhanced CT or MR [3]. The late phase of the CEUS exam has been shown to be the most critical in distinguishing benign from malignant liver lesions [4]. Benign liver lesions generally have persistent enhancement with hypervascular or iso- vascular appearance relative to the adjacent liver par- enchyma [4]. Malignant lesions generally have washout and become hypovascular in appearance; although, hepatocellular adenomas may washout, and therefore the appearance can overlap malignant lesions [5–8]. As with all other modalities, CEUS evaluation of liver lesions should take into account the clinical context, particularly considering the presence or absence of risk factors for HCC. Herein, the CEUS imaging characteristics of benign liver lesions will be reviewed; including the CEUS appearance of hepatic cysts, hemangiomas, focal fat, focal nodular hyperplasia (FNH), hepatocellular ade- nomas (HCA), abscesses, and traumatic lesions (sum- marized in Table 1). Cystic liver lesions Liver cysts are commonly found incidentally and are usually benign with little clinical significance. Simple cysts appear as completely anechoic, rounded, or ovoid lesions at gray-scale ultrasound with imperceptible walls and posterior acoustic enhancement. At CEUS, there is Correspondence to: Jessica G. Zarzour; email: jgzarzour@uabmc.edu ª Springer Science+Business Media, LLC, part of Springer Nature 2017 Abdominal Radiology Abdom Radiol (2017) DOI: 10.1007/s00261-017-1402-2