Liver lesions

FNH and hepatocellular adenoma (HCA) is liver lesions of hepatocellular origin. Whereas FNH commonly occurs, HCA is very rare. Distinguishing FNH from HCA is of great importance clinically, as FNH is considered a benign lesion and needs no further management. In contrast, HCA, according to its subtype, can be considered a borderline tumour due to the risk of haemorrhage, growth, and even malignant transformation, and therefore requires individualised management. The genotype/phenotype classification of HCA is an evolving issue, and there is now a recent HCA molecular classification by which to stratify patients according to the risk of complications. On imaging, HCA is no longer a distinct entity, and imaging features reflect the tumour subtypes. Contrast-enhanced MRI is much more accurate because of its ability to visualise the textural composition of the HCA. However, even after the administration of MRI hepatobiliary contrast agents, a small proportion of HCA subtypes still show either inhomogeneous uptake or inhomogeneous washout in the hepatobiliary phase (HBP); making them difficult to differentiate from FNH on the basis of imaging presentation alone. This may pose a diagnostic dilemma as both FNH and HCA tend to occur in women of child-bearing age. Clinical presentation and risk factors, male gender, patient age, the presence of storage disease, obesity, metabolic or inflammatory syndrome, hepatitis, alcohol abuse and tumour over five cms, as well as significant growth have been identified as factors associated with an HCA-subtype of higher malignant potential. In difficult cases, histology remains the gold standard.

Quantitative MR imaging offers a multiparametric approach to assess the severity of hemochromatosis, nonalcoholic fatty liver disease, chronic viral hepatitis, and cirrhosis. The most validated methods are multi-echo gradient-echo MR imaging to quantify hepatic iron and fat, as well as MR elastography to quantify liver fibrosis, cirrhosis, and potentially liver inflammation. Alternative methods for liver fibrosis staging include apparent diffusion measurements and T1 relaxometry, without or with gadoxetic acid enhancement. The diagnostic performance of these methods should be further compared to that of MR elastography. MR imaging has the potential to become a method of virtual biopsy that may decrease the need for invasive reference examinations in diffuse liver diseases. The integration of ultrasound and MR imaging biomarkers with blood sample biomarkers to further improve the assessment of diffuse liver diseases is a point of current research.

The use of contrast-enhanced ultrasound (CEUS) to assess focal liver lesions is now well established, with superb ability to characterise lesions visually. The ability to measure parameters of the CEUS examination objectively is realised by the fact that the microbubble contrast agent is truly intravascular and has a linear dose response. This differs from the dynamics of other contrast agents used in CT and MR imaging. The drawback of CEUS is the ability to identify the lesion clearly. The use of time intensity curves, particularly calculating washout is undergoing continuing research, and the usefulness is extended to other organs such as the kidney and testis to evaluate different enhancement patterns. Segmentation, colour mapping and use of artificial intelligence will move the usefulness of objective measurements of dynamic CEUS imaging, particularly of liver lesions. The development of ultrasound elastography has allowed the definition of the levels of liver fibrosis, with different techniques available, impacting on clinical management of chronic liver disease. All these new techniques, combined as multiparametric ultrasound (MPUS), as advanced the practice of ultrasound imaging, and is a robust, patient-friendly imaging tool.

We will discuss the role of multiparametric MRI including T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI) and dynamic post-contrast T1WI imaging for the characterisation of focal liver lesions: to differentiate benign and malignant lesions and characterise subtypes of malignant lesions based on a combination of imaging features. We will also discuss the role of DWI and dynamic contrast-enhanced MRI for assessing tumour response. Finally, we will discuss future directions such as radiomics methods used for assessing liver tumours and tumour response.

The differential diagnosis of cystic liver lesions is as broad as their clinical significance, which ranges from benign to malignant and/or potentially lethal conditions. These lesions include foregut and ductal plate malformations, infectious conditions, primary and secondary neoplasms and traumatic/iatrogenic fluid collections. The number of lesions, morphology, fluid content characteristics, presence/absence of septae and/or solid components are the key imaging features for the diagnostic approach, and different imaging modalities pose different advantages and disadvantages for their characterisation. Given imaging characteristics may overlap between distinct conditions, patient history and laboratory data should be integrated to allow a more definitive diagnosis.

Haemangiomas are common focal liver lesions, generally detected in the workup of asymptomatic patients and do not require further workup, follow-up, or treatment. From the morphologic point of view, they can be classified as small (capillary) or large, with cavernous vascular spaces that may prone to show thrombosis, calcifications and hyalinisation. The polymorphic imaging appearance of haemangiomas depends on their histological features and flow pattern. The widespread use of cross-sectional imaging has allowed a better characterisation of this benign vascular tumour, and for this lecture, illustrative cases will be displayed especially using CT and multiparametric MRI including hepato-biliary contrast agents. Haemangiomas imaging findings may range from the commonly known aspects especially after extra-cellular Gd-chelates administration to atypical patterns where its recognition and positive diagnosis may not be so straightforward. The scope of the present lecture to present and discuss the patterns of those vascular liver lesions, describing normal findings, pitfalls, potential differentials, confounders and complications.