LIVER METASTASES

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  • The pathology of metastatic deposits in the liver closely resembles the primary tumor, i.e. they are usually as vascular as their primary tumors
  • In general, most metastases are hypovascular, but some primaries characteristically have hypervascular metastases
  • Hypervascular metastases
    • Carcinoids
    • Leiomyosarcomas
    • Neuroendocrine tumors
    • Renal carcinomas
    • Thyroid carcinomas
    • Choriocarcinomas
    • Occasionally pancreas, ovary, or breast
  • Blood flow increases in all metastases, even hypovascular tumors
  • Neovascularity, vascular encasement, and arteriovenous shunting are rare
  • Large metastases can outgrow their blood supply leading to central necrosis
  • CT findings
    • CT is the study of choice for evaluating liver metastases
    • CT is the most sensitive technique for the detection of liver metastases (80-90% sensitivity and 99% specificity for contrast-enhanced scans)
    • Most liver metastases are hypovascular compared with surrounding parenchyma and therefore most lesions appear either hypoattenuating or isoattenuating relative to the surrounding normal liver
    • Most studies of the liver for metastatic disease are contrast-enhanced
      • Hypovascular lesions are more easily detected using contrast-enhancement
    • On contrast-enhanced scans, liver metastases may display slight peripheral enhancement with a hypoattenuating center
    • The margin of the lesions can vary from well defined to ill defined
    • Hyperattenuating lesions are uncommon
      • On the portal venous phase of scanning, some highly vascular primary tumors such as renal cell carcinomas, pancreatic islet cell tumors, pheochromocytomas, melanomas, and breast carcinomas, may appear as isoattenuating to normal liver
    • Differential diagnosis
      • Multiple hemangiomas can be mistaken for metastases
      • Cysts show no enhancement
      • Focal nodular hyperplasia (FNH) -- may look like vascular metastases
      • Focal fatty sparing in a diffusely fatty liver can simulate metastases
    MRI findings
    • MRI is usually used as a as problem-solving rather than a primary technique in the diagnosis of liver metastases
    • Most liver tumors, benign or malignant, appear as hypointense lesions on T1-weighted images andhyperintense lesions on T2-weighted images
    • Gadolinium-enhanced MRI improves both the detection of focal liver masses and the differentiation of benign from malignant lesions
    • Hemangiomas are reliably diagnosed with MRI 
    General US findings
    • US appearance of liver metastases is nonspecific
    • Hepatomegaly
    • The liver surface may appear nodular or lobular
    • Multiple hepatic nodules of different sizes within the liver is nearly always due to metastases

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