Liver shear-wave elastography: From the guidelines to the daily practice

Shear wave elastography (SWE) has been accepted by guidelines as a reliable substitute of liver biopsy in several clinical scenarios. Guidelines on the use of SWE techniques for liver stiffness assessment have been produced by several Federations or Societies, including EFSUMB, WFUMB, EASL-ALEH, APASL, and AGA. Moreover, the Society of Radiologists in Ultrasound (SRU) has released a consensus statement on the use of elastography in diffuse liver disease. EFSUMB, WFUMB and SRU have recently updated the previously published guidelines/consensus. All guidelines recommend to follow a protocol for stiffness measurements. Moreover, several confounding factors that influence liver stiffness independently from the stage of liver fibrosis have been identified, including hepatic inflammation, bile duct obstruction, congestion, and infiltrative liver diseases. These factors should be taken into account to avoid overestimation of liver fibrosis. The influence of liver steatosis is still a matter of debate with conflicting results in the literature. In chronic liver disease, it is important to identify patients with severe fibrosis or cirrhosis, because they need follow-up. The Baveno VI conference has highlighted that the spectrum of fibrosis is a continuum; therefore, for asymptomatic patients with severe fibrosis or liver cirrhosis at an early stage, the term “compensated advanced chronic liver disease (cACLD)” has been proposed. For the acoustic radiation force impulse (ARFI)-based techniques, the SRU update consensus has highlighted that the overlap of liver stiffness (LS) values between METAVIR fibrosis stages is as large if not larger than the difference between vendor’s techniques. Therefore, based on published studies, a “rule of 4” for fibrosis staging with all the ARFI-based techniques in patients with chronic viral hepatitis or NAFLD has been suggested: LS≤5kPa has high probability of being normal; LS<9 kPa, in the absence of other clinical signs of chronic liver disease, rules out cACLD; values between 9kPa and 13kPa are suggestive of cACLD but may need further test for confirmation; values >13kPa are highly suggestive of cACLD. There is a probability of clinically significant portal hypertension with LS values >17kPa, but additional tests may be required. The SRU consensus has also proposed to use the delta change of LS value over time instead of absolute values to follow-up patients with chronic liver disease. In patients with viral hepatitis, LS baseline value must be that obtained after viral eradication or suppression.