Ultrasonography of liver tumors

Ultrasonography of liver tumors involves two stages: detection and characterization. Tumor detection is based on the performance of the method and should include morphometric information (three axes dimensions, volume) and topographic information (number, location specifying liver segment and lobe/lobes). The specification of these data is important for staging liver tumors and prognosis. Tumor characterization is a complex process based on a sum of criteria leading towards tumor nature definition. Often, other diagnostic procedures, especially interventional ones are no longer necessary. Tumor characterization using the ultrasound method will be based on the following elements: consistency (solid, liquid, mixed), echogenicity, structure appearance (homogeneous or heterogeneous), delineation from adjacent liver parenchyma (capsular, imprecise), elasticity, posterior acoustic enhancement effect, the relation with neighboring organs or structures (displacement, invasion), vasculature (presence and characteristics on Doppler ultrasonography and contrast-enhanced ultrasound (CEUS). The substrate on which the tumor condition develops (if the liver is normal or if there is evidence of diffuse liver disease) and the developing context (oncology, septic) are also added. Particular attention should be paid to the analysis of the circulatory bed. Microcirculation investigation allows for discrimination between benign and malignant tumors. Characteristic elements of malignant circulation are vascular density, presence of vessels with irregular paths and size, some of them intercommunicating, some others blocked in the end with "glove finger" appearance, the presence of arterio-arterial and arterio-venous shunts, lack or incompetence of arterial precapillary sphincter made up of smooth musculatures. Diagnosis and characterization of liver tumors require a distinct approach for each group of conditions, using the available procedures discussed above for each of them. The correlation with the medical history, the patient's clinical and functional (biochemical and hematological) status are important elements that should also be considered.

Benign liver tumors Benign liver tumors generally develop on normal or fatty liver, are single or multiple (generally paucilocular), have distinct delineation, with increased echogenity (hemangiomas, benign focal nodular hyperplasia) or absent, with posterior acoustic enhancement effect (cysts), have distinct delineation (hydatid cyst), lack of vascularization or show a characteristic circulatory pattern, displace normal liver structures and even neighboring organs (in case of large sizes), are quite elastic and do not invade liver vessels. The patient has a good general status, as tumors are often asymptomatic, being incidentally discovered.

Liver cysts They can be single or multiple, with variable size, generally less than 20 mm (congenital). Rarely, sizes can reach several centimeters, leading up to the substitution of a whole liver lobe (acquired, parasitic). They may be associated with renal cysts; in this case the disease has a hereditary, autosomal dominant transmission (von Hippel Lindau disease). The ultrasound appearance is a well defined lesion, with very thin, almost unapparent walls, without circulatory signal at Doppler or CEUS investigation. The content is transonic suggesting fluid composition. The presence of membranes, abundant sediment or cysts inside is suggestive for parasitic, hydatid nature. Posterior from the lesion the acoustic enhancement phenomenon is seen, which strengthens the suspicion of fluid mass. They typically displace normal liver vessels but no vascular or biliary invasion occurs.

Hemangioma

It is the most common liver tumor with a prevalence of 0.4 – 7.4%. It is generally asymptomatic but also can be associated with pain complaints or cytopenia and/or anemia when it is very bulky. It is unique or paucilocular. It can be associated with other types of benign liver tumors. Characteristic 2D ultrasound appearance is that of a very well defined lesion, with sizes of 2–3 cm or less, showing increased echogenity and, when located in contact with the diaphragm, a "mirror image" phenomenon can be seen. When palpating the liver with the transducer the hemangioma is compressible sending reverberations backwards. Doppler exploration reveals no circulatory signal due to very slow flow speed. CEUS investigation has real diagnosis value due to the typical behavior of progressive CA enhancement of the tumor from the periphery towards the center. The enhancement is slow, during several minutes, depending on the size of hemangioma and on the presence (or absence) of internal thrombosis. During late (sinusoidal) phase, if totally "filled" with CA, hemangioma appears isoechoic to the liver. Deviations from the above described behavior can occur in arterialized hemangiomas or those containing arterio-venous shunts. In these cases, differentiation from a malignant tumor is difficult and requires other imaging procedures, follow up and measurements of the tumor at short time intervals.

Focal nodular hyperplasia

It is a tumor developed secondary to a circulatory abnormality with abundant arterial vessels having a characteristic location in the center of the tumor, within a fibrotic scar. A radial vessels network develops from this level with peripheral orientation. The tumor's circulatory bed is rich in microcirculatory and portal venous elements. The incidence is higher in younger women and tumor development is accelerated by oral contraceptives intake. 2D ultrasound appearance is a fairly well-defined mass, with variable sizes, usually single, solid consistency with inhomogeneous structure. Rarely the central scar can be distinguished. Spectral Doppler examination detects central arterial vessels and CFM exploration reveals their radial position. CEUS examination shows central tumor filling of the circulatory bed during arterial phase and completely enhancement during portal venous phase. During this phase the center of the lesion becomes hypoechoic, enhancing the tumor scar. During the late phase the tumor remains isoechoic to the liver, which strengthens the diagnosis of benign lesion.

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