Normally, we compare the renal parenchymal echogenicity to that of liver on the right and spleen on the left. But if the patient has fatty liver, this can get confusing.
How does fatty liver appear on ultrasound? – The echogenicity of the normal liver is almost the same or slightly more than that of the renal cortex or spleen. In addition, intrahepatic vessels are sharply demarcated. In cases of fatty liver, echogenicity of the liver exceeds that of renal cortex and spleen (this change is easily identifiable most of the time). In severe cases, the diaphragm might lose definition because the liver parenchyma becomes as bright as this fibrous structure. In early stages, intra-hepatic vessels may be well-delineated because of the contrasting echogenicity (vessels are anechoic/black) but eventually, they lose the definition, and everything appears hazy.
In such cases, bilateral renal parenchymal echogenicity can be compared to that of spleen (not fool proof). However, we know that increased kidney echogenicity is just one component of assessing acute vs chronic kidney disease. Here is an example of fatty liver obtained from an asymptomatic nephrology clinic patient. Note how bright the liver is compared to that of spleen. Gain settings have not been changed on the machine.
Another example: Compare the echogenicity of liver and spleen