Imaging of hepatic steatosis and fatty sparing

doi:10.1016/j.ejrad.2006.11.005

European Journal of Radiology

Volume 61, Issue 1, January 2007, Pages 33-43

https://doi.org/10.1016/j.ejrad.2006.11.005 Get rights and content

Abstract

Radiology has gained importance in the non-invasive diagnosis of hepatic steatosis. Ultrasonography is usually the first imaging modality for the evaluation of hepatic steatosis. Unenhanced CT with or without dual kVp measurement and MRI with in and out of phase sequence can allow objective evaluation of hepatic steatosis. However, none of the imaging modalities can differentiate non-alcoholic steatohepatitis/fatty liver disease from simple steatosis. Evaluation of hepatic steatosis is important in donor evaluation before orthotopic liver transplantation and hepatic surgery. Recently, one-stop shop evaluation of potential liver donors has become possible by CT and MRI integrating vascular, parenchymal, volume and steatosis evaluation. Moreover hepatic steatosis (diffuse, multinodular, focal, subcortical, perilesional, intralesional, periportal and perivenular), hypersteatosis and sparing (geographic, nodular and perilesional or peritumoral) can cause diagnostic problems as a pseudotumor particularly in the evaluation of oncology patients. Liver MRI is used as a problem-solving tool in these patients. In this review, we discuss the current role of radiology in diagnosing, quantifying hepatic steatosis and solutions for diagnostic problems associated with fatty infiltration and sparing.

Introduction

Hepatic steatosis is characterized by increased triglyceride content of liver due to a variety of causes [1], [2], [3]. Most important factors for the development of steatosis are alcoholism, non-alcoholic steatohepatitis (NASH) and obesity [4]. Focal fatty infiltration and sparing develop secondary to altered liver vascular supply most commonly adjacent to liver capsule [5].

This review discusses methods for detection and quantification of steatosis including ultrasonography, CT and MRI, and radiologic findings of different forms of steatosis (diffuse, hypersteatosis multiple nodules, focal, subcortical, perilesional, intralesional, periportal and perivenular) and fatty sparing (geographic, nodular and perilesional) (Table 1).

Section snippets

Ultrasonography (US)

US is the simplest method for crude estimation of liver steatosis. However, accurate quantification of steatosis is not feasible with the current technology. Steatosis appears bright or hyperechoic relative to adjacent right kidney or spleen [6], [7], [8]. Sensitivity of US increases with increasing degree of steatosis [7], [9]. Mild steatosis is characterized by mild increase in liver echogenicity. Moderate steatosis can be diagnosed with increased liver echogenicity that obscures

Hepatic steatosis

A variety of clinical disorders is associated with diffuse steatosis including obesity, malnutrition, diabetes mellitus, steroid use, alcoholic liver disease, pregnancy and hepatitis [1], [2], [3], [4], [5], [6]. Major two causes of hepatic steatosis are alcoholic liver disease and non-alcoholic steatohepatitis (NASH). Latter cause has emerged recently as a distinct clinical entity, which is characterized by inflammation and fibrosis associated with steatosis [4], [49], [50]. Although

Focal geographic and nodular fatty sparing

Hepatic fatty sparing occurs because of a similar mechanism leading to the formation of focal steatosis which is altered liver hemodynamics caused by small veins entering liver (Fig. 8) [5], [7], [66], [77], [78], [79].

On ultrasonography focal fatty sparing appears as a hypoechoic lesion in a steatotic liver. On CT it appears as hyperdense areas within diffusely hypodense liver parenchyma. MRI allows characterization of these lesions by using in and out phase T1-weighted gradient echo sequence.

Conclusion

In conclusion, cross-sectional imaging plays an important role in the diagnosis of hepatic steatosis. MRI appears to be the most sensitive test for the diagnosis and quantification of steatosis. CT and ultrasonography are also widely used for the diagnosis of steatosis. However, multicenter trials and standardization of radiologic techniques (CT, MRI and ultrasonogarphy) and parameters are needed in order to objectively assess the role of radiology in the quantitative assessment of steatosis.

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