Even the round ligament appearing in a transverse scan as a hyperechoic target lesion may resemble a solid tumor (Fig. 4.4): its origin from the umbilical portion, its linear shape once the scan is sagittal would disclose its real nature. A frequent source of misinterpretation is represented by the so-called skip-areas, which are portions of the liver with different intracellular distribution of lipids resulting in areas with different echogenicity [1]. These areas are typically located around the gallbladder (Fig. 4.5) or around the main portal pedicles (Fig. 4.6): their shape, the fact that vessels are passing through without distortions, and, not last, the mentioned typical locations should ensure their proper interpretation. There is an artifact being a true optical illusion which is called the mirror effect : in cases where a lesion is just anterior to other structures being a barrier for the diffusion of the ultrasonic waves, a reflection of the lesion itself can appear posteriorly, mimicking the reflection of an image in front of a mirror both without (Fig. 4.7a, b) and with contrast enhancement (Fig. 4.8).

IOUS allows the detection of new lesions in around 30 % of cirrhotic patients [2]. However, most of the nodules detected by IOUS in these patients are not really tumors: in this way, IOUS introduces the risk of overestimating the tumor stage (Fig. 4.9). Indeed, except for those nodules with mosaic ultrasonographic patterns (Fig. 4.10a), which are malignant in 84 % of cases, only 24–30 % of hypoechoic nodules (Fig. 4.10b), and 0–18 % of those hyperechoic (Fig. 4.10c) are neoplasm [2, 3]. To overcome this problem even biopsy may not be adequate. The only nodule which can be easily differentiated intraoperatively from an HCC or a liver metastasis is the small hemangioma which is often discovered primarily by IOUS: it has a typical ultrasonographic pattern and moreover when compressed changes its size and appearance (Fig. 4.11a, b). This is based essentially on the different stiffness of the hemangioma compared to other lesions. Stiffness measurements are advantageous in this respect. In fact, intraoperative elastography can afford lesion differentiation based on tissue elasticity expressed on the IOUS screen by differences in colors (Fig. 4.12a, b). Therefore, some authors have introduced a classification for differentiating HCC from metastastic nodules based on their tissue elasticity at intraoperative elastography [4]. In this sense, other authors have proposed the use of elastography to check in real time the completeness of intraoperative tumor ablation [5]. Chapter 5 describes how CEIOUS is starting to play an important role in this respect, and most likely will become more relevant in the near future.