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Castán et al. Radiology of hepatocarcinoma in non-cirrhotic patients

stages of cirrhosis, it is possible to see peripheral the case of diffusion and MRI elastography, perfusion
hypodense areas, with retraction of the liver contour measures the liver fibrosis with indirect markers.
and delayed enhancement, corresponding to focal Hagiwara et al. [38] showed an increase in absolute
confluent fibrosis. Signs of portal hypertension are blood flow, blood fraction, volume of distribution
similar to those seen with US: portal vein dilation, and the mean transit time, and a decreased portal
varicose veins and splenomegaly. venous fraction in patients with advanced liver
fibrosis compared to patients with early-stage fibrosis.
MRI shows greater tissue contrast than CT and US, However, several factors may affect the correlation
resulting in increased information on the changes in between perfusion parameters and fibrosis (cardiac
the structure of the liver parenchyma. In patients with output, fasting, liver congestion, liver inflammation,
advanced cirrhosis, MRI may show a heterogeneous liver damage, and portal venous flow).
liver parenchyma with regenerative nodules and
fibrous septa or bridges. The regenerative nodules The study of liver fibrosis by molecular MRI is still in
are isointense or hyperintense on T1 sequences and its development phase and is emerging as a valuable
isointense or hypointense on T2 sequences. The tool for the non-invasive detection of early-stage liver
fibrous septa are crosslinks of low signal intensity on fibrosis. Compared to normal liver, the amount of
T1 sequences and high intensity on T2. type I collagen in fibrotic livers increases significantly
(from 36% to 53%). [39] Therefore, type I collagen
Areas of confluent focal fibrosis, which appear as can be used as a molecular target for detection of
hypointense lesions on T1 and hyperintense on liver fibrosis by molecular MRI. Research on the
T2, can also be identified. Contrast media based development of specific radiopharmaceuticals which
on gadolinium are accumulated in the extracellular can target only the extracellular matrix collagen for the
compartment and are deposited on the fibrous tissue diagnosis of early-stage fibrotic livers is underway.
in the liver. Thus, most contrast agents based on
gadolinium improve signal of liver fibrosis in T1, From the above it is concluded that US, CT, and
particularly in the venous phase and equilibrium conventional MRI have a high specificity for the
phase. It is also possible, as with US, to perform diagnosis of cirrhosis, but have a low sensitivity in the
an elastography by MRI, quantifying liver stiffness early stages of the disease. In pre-cirrhotic patients,
by analyzing the propagation of mechanical waves the liver parenchyma usually appears normal on
through the tissue. It allows assessment of all the liver MRI or only a mild non-specific heterogeneity of the
surface, unlike US elastography, which only evaluates parenchyma is identified. Using discrete elastography
the outermost regions. It has high sensitivity (92%) can improve the sensitivity in detecting early cirrhosis.
[35]
and specificity (95%) for the detection of liver fibrosis. Göbel et al. [40] showed a 10% increase in sensitivity
However, it is a technique of limited availability today, for detection of liver cirrhosis with TE compared to
with long turnaround times and cannot be done to the use of routine screening. They also showed that
livers with iron overload due to noise signal artifacts. the combination of TE with conventional US further
improves diagnostic accuracy. However, at present,
Diffusion technique evaluates the diffusion of the with current imaging techniques, the absence of
protons of water molecules within tissues. It is routinely fibrosis or cirrhosis in patients with lesions suspicious
used for liver testing. Calculating the apparent diffusion of HCC cannot be confirmed.
coefficient (ADC) can facilitate the assessment of liver
fibrosis. It has been shown that ADC values decrease Liver biopsy is considered the gold standard for
as liver fibrosis increase. Bakan et al. [36] detected no evaluating fibrosis. [41] However, it is an invasive
significant differences in ADC values between stages procedure which can be associated with pain and
F0 and F1 and between F1 and F2. Another study, with a 0.5% risk of complications. [42] Moreover, this
however, showed significant differences in ADC values technique has limitations: first, biopsy analyzes a small
between the stages F0 and F4. [37] Together, these part of the parenchyma, leading to sampling errors if it
findings suggest that diffusion technique is not reliable has been done in an area with less fibrotic component;
for distinguishing the early stages of liver fibrosis. second, there is a 20% intra- and inter-observer
variability in the histological assessment; [43] and third,
Vascular changes that occur as a result of cirrhosis it should be noted that the biopsy does not predict
can be detected after the administration of a disease progression and therefore additional biopsies
paramagnetic contrast agent and can be useful to would be needed after starting treatment for follow-up.
quantify the state of parenchymal microcirculation.
Liver fibrosis decreases portal venous flow, increases In the absence of morphological signs of cirrhosis in
arterial blood flow and forms intrahepatic shunts. As is patients with suspicious lesions of HCC, histological
8 Hepatoma Research ¦ Volume 3 ¦ January 12, 2017