Ultrasound images Fatty infiltration (steatosis)

The process of accumulation of fat within the hepatic cells may be either focal (see above) or diffuse.
Related to various conditions such as alcoholism, obesity and diabetes, it is associated with any process which alters liver metabolism and it is
reversible in many circumstances. The acoustic properties of fat differ from those of normal liver tissue. The liver appears hyperechoic as
the fat globules provide interfaces which are highly reflective. As the level of fat deposition increases, the level of echogenicity may reach that of the highly
reflective portal tract walls. This has the effect ofbreducing the prominence of the portal tracts (Fig. below) and making the liver appear smooth and
homogeneous, with closely packed, fine echoes.bThe contrast between the liver and parenchyma of the right kidney is therefore increased (a particularly
useful sign confirming that the correct gain settings have been used). Hepatomegaly is also a feature, though not invariably.
Finally, the attenuation of fat is greater than that of normal liver tissue; this has the effect of reduced penetration in the far field, rather as if the
time gain compensation (TGC) paddles or slope control had been incorrectly set. In severe cases of infiltration, most of the sound is reflected back to
the transducer in the first few centimetres, creating a highly reflective near-field band through which the sound is unable to penetrate.
Fatty infiltration itself is not usually a significant finding; however it often occurs in conjunction with other significant diffuse processes such
as cirrhosis. Its increased attenuation reduces the ability of ultrasound to exclude other disease or focal lesions and therefore CT is often a useful
adjunct.

image

Fatty infiltration increases the hepato-renal contrast. The portal tracts are reduced in prominence,
giving a more homogeneous appearance.

image

Attenuation of the beam by fat prevents demonstration of far-field
structures.

 

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