Differentiation from benign lesions such as cysts or hemangiomas is essential. On heavily T2-weighted images, metastases are usually less bright than hemangiomas or cysts, a fact that has been used for characterization purposes. Hypervascular and cystic metastases may be very bright on T2-weighted images, and sole reliance on T2 signal characteristics may potentially lead to the incorrect characterization of these lesions as cysts or hemangiomas. Contrast-enhanced studies may be necessary for characterization in some patients. Gadolinium-enhanced MR does not increase detection of liver metastases, but it does help with characterization.
Metastases have a variable appearance following gadolinium administration.
They may be either hypervascular and enhance on the early arterial phase or hypovascular and enhance slowly . They often enhance with a complete peripheral ring pattern. Detection of liver mets increases significantly after ferumoxides administration. The liver loses signal intensity after contrast but the mass, which has no RES activity, does not and appears brighter. Since cirrhotic livers contain areas of nodules and fibrosis, diagnosis of hepatocellular carcinoma may be particularly challenging.