Ultrasound Unit, Infectious Diseases Department, Fondazione IRCCS Policlinico San Matteo, University of Pavia
In chronic viral hepatitis the stage of liver fibrosis influences patient’s prognosis and survival. For decades liver histology has been considered the reference standard for the assessment of liver fibrosis despite the intraobserver and interobserver variability in the staging, and some morbidity and mortality risks. In the last few years, due to the limitations of liver biopsy as well as the development of new antiviral drugs, the use of liver biopsy in the management of patients with chronic viral hepatitis has rapidly decreased whereas the noninvasive methods for the assessment of liver fibrosis are increasingly been used. The first elastography technique available has been transient elastography. Several studies and meta-analyses have shown that transient elastography is an accurate method in the staging of liver fibrosis. Even though US-based, it is not a B-mode imaging technique and cannot be performed in patients with perihepatic ascites. B-mode elastography techniques have the advantage of being integrated into US systems, thus the measurements of liver stiffness may be guided by the B-mode image - that allows to choose an area of liver parenchyma better suited for stiffness assessment, i.e. free of large vessels and focal lesions - and the same equipment is used for both conventional US and stiffness assessment. In patients with chronic viral hepatitis elastography plays an important role in the noninvasive assessment of liver fibrosis, allowing not only an accurate evaluation before treatment but also the estimate of the progression or regression of liver fibrosis over time. Based on a meta-analysis of cohort studies, the degree of liver stiffness is associated with risk of decompensated cirrhosis, hepatocellular carcinoma, and death in patients with chronic liver diseases. Therefore, measurements of liver stiffness might be used in risk stratification. To correctly read the results, it should be kept in mind that elastography assesses liver elasticity that could be modified by factors other than fibrosis, such as oedema, inflammation, extra-hepatic cholestasis, or congestion. Thus, the results should always be interpreted in the clinical settings.