Liver Masses: A Clinical, Radiologic, and Pathologic Perspective

Sudhakar K. Venkatesh; Vishal Chandan; Lewis R. Roberts

Disclosures

Clin Gastroenterol Hepatol. 2014;12(9):1414-1429. 

In This Article

The Use of Multiphasic Cross-sectional Imaging in the Evaluation of Liver Masses

Cross-sectional imaging with CT or MRI is enhanced by the use of intravenous contrast agents and dynamic multiphasic examination techniques. The liver has 3 distinct phases after intravascular contrast agent is injected via a peripheral vein. The arterial phase occurs 25 to 35 seconds after peripheral contrast injection and is caused by the direct infusion of arterial blood with a high concentration of contrast from the heart through the hepatic artery into the liver. Next, the portal venous phase occurs 60 to 75 seconds after contrast injection as blood from the gastrointestinal tract is collected in the portal vein for processing in the liver. Finally, in the venous phase, blood from the liver is collected into the hepatic veins, which converge to the inferior vena cava for return to the right atrium. The intravascular contrast leaks through the liver sinusoids into the extracellular space and about 3 to 5 minutes after injection, the extracellular contrast reaches equilibrium with the concentration in the vascular system. This is known as the equilibrium phase. This unique blood supply to the liver is exploited by contrast imaging techniques because many mass lesions have characteristic patterns of appearance in the arterial, portal venous, and equilibrium phases. Newer contrast agents that are taken up by functioning hepatocytes and excreted into bile, such as disodium gadoxetate (Gd-EOB-DTPA; Eovist; Bayer Corporation, Pittsburgh, PA) and gadobenate dimeglumine (Gd-BOPTA; MultiHance; Bracco Diagnostics Inc, Princeton, NJ), provide further phenotypic characterization of liver masses and are particularly useful in the differentiation of adenomas from focal nodular hyperplasias (FNHs) and the diagnosis of HCC and metastases. The enhancement of hepatocytes with these hepatobiliary contrast agents in the hepatocyte or parenchymal phase typically peaks between 20 and 60 minutes after intravenous injection. Uptake of gadoxetate and gadobenate is believed to occur mainly through cell membrane proteins in the bile canaliculi and ducts, including organic anion transporting polypeptides and multidrug resistance protein.[10] The expression of these proteins is usually suppressed in adenomas and HCCs and lack of the hepatocyte phase enhancement is useful in differentiating them from FNH.

Imaging characteristics on MRI are useful in differentiating HCC from other hepatic lesions. The T2-weighted sequence is sensitive to alterations in water content and pathologic tissues appear brighter than normal tissues. Most HCCs show high signal intensity on T2-weighted images compared with benign lesions such as adenomas and FNHs. The in-phase and opposed-phase sequences in which regions of fat deposition show characteristic signal loss in the opposed phase can be useful in differentiating HCC from focal fat deposition or focal fat sparing. Diffusion-weighted imaging (DWI) highlights the areas of restricted diffusion and is sensitive to focal abnormalities. Malignant lesions show restricted diffusion on DWI and appear brighter. However, this finding lacks sufficient specificity to be the sole diagnostic criterion in routine clinical practice. Moreover, combining DWI with contrast-enhanced MRI provides high accuracy for the detection and characterization of HCCs.[11,12]

Recent advances in CT provide higher spatial and temporal resolution for the evaluation of liver tumor hemodynamics, while also providing 3-dimensional or 4-dimensional imaging for treatment planning. Perfusion CT provides quantitative information about arterial perfusion in HCC, allowing the evaluation of tumor angiogenesis and response to therapy.[13,14] Dual-energy CT (performed with 2 different energy spectra) improves detection and assessment of hypervascular tumors.[15] Magnetic resonance elastography and acoustic radiation force impulse imaging are currently under investigation and may potentially be useful techniques in the characterization of liver masses.[16–19]

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