Metastatic liver disease is the most frequent malignant hepatic affliction, the liver being the most common site for secondary malignant involvement. Depending on the original organ, the liver metastases may be hyper-vascular or hypo-vascular, small or large; the latter can present roughly central necrotic areas. All metastases are characterized by some degree of arterial neoangiogenesis (macro-vessels in peripheral margins and micro-vessels in the central zone) and lack or reduced portal supply. The total hematic volume of the lesion is inferior to the surrounding healthy parenchyma. Some metastases like those from neuro-endocrine, thyroid, lymphoma, plasmacytoma, and kidney tumors may have a superior arterial supply to the surrounding parenchyma but with a loss of portal vessels so at least the blood volume is inferior. On conventional US, metastases may present hypo-, iso- or hyper-echoic patterns matching the primary tumor or necrosis or calcification. Usually small lesions appear as homogeneous hypo-or iso-echoic solid nodules, while the larger lesions frequently show an inhomogeneous aspect with hypo-echoic areas due to necrosis and iso-, hyper-echoic areas related to fibrosis and calcification.
The margins may be reasonably well-defined, and sometimes a halo sign or target pattern can be found. Cystic appearances may be related to ovarian and neuro-endocrine primary tumors (Cosgrove 2001; Harvey and Albrecht, 2001). Color Doppler may detect flow signals in the outer zone of the lesions, whereas this finding in the inner zone is relatively rare (Numata et al., 1997). Depending on whether the lesion is hyper- or hypo- vascularized CEUS may present different aspects (Albrecht et al., 2004; Catalano et al., 2005) (Fig. 2 a-d).
Multiple liver lesions in segment 7, solid hyperechoic with intralesional hyperechoic calcifications. In arterial and portal phase complete early enhancement. In parenchymal phase it is found lack of enhancement. In late parenchymal phase others lesions about 5mm diameter show lack of enhancement.
C.R.: metastases and micro-metastases
Focal liver lesions in segment 5, solid iso-hypoechoic. In arterial phase complete early enhancement. In portal and late parenchymal phase it is found lack of enhancement.