ReviewImaging of hepatic steatosis and fatty 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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