Fatty infiltration of the liver on CT is a common finding that often has no symptoms. It can be due to a variety of causes to include: alcohol abuse, obesity, diabetes, metabolic diseases, drugs, pregnancy and hepatitis to name some. It can progress to cirrhosis in a minority of patients. It can be reversed with modification of the underlying condition. For example, losing weight and improving diet, abstaining from alcohol, or removing offending drug.
The diagnosis of fatty liver on CT is best made on a scan without contrast. The liver will appear lower in density then the spleen or lower then 40 hounsfield units. Hounsfield units are a way to quantify the density or appearance of various structures on CT. Basically, fatty infiltration is a misnomer because fat gets deposited inside the cells rather then around them.
I see fatty infiltration on a daily basis and mention it because it can progress to end stage liver disease requiring transplantation. It can be reversed by modifying the causative factor. In practice, I see it most common with obesity, alcohol abuse, and diabetes. This is mostly a non urgent issue unless it’s associated with hepatitis. The most severe and unusual appearances happen with alcohol abuse in my experience. I have even seen it mimic cancer of the liver.
Fatty infiltration of the liver can pose some imaging challenges because it is not always uniform in appearance and throughout the liver. Sometimes the fatty infiltration is patchy or uneven. Then some parts of the liver will look darker then others. An experienced radiologist will recognize this as typical fat in the liver with areas of sparing. The areas of fat involvement will look geographic, like states on the US map. The area will not displace blood vessels since this is normal liver with fat inside the cells rather then a mass which would push vessels.
There are some instances where the appearance of fatty infiltration can be tricky and require further testing. Sometimes, the fatty infiltration will spare a part of the liver and look round or mass like. This makes it very difficult to exclude a mass. In these cases, an abdominal MRI will allow the distinction to be made.
Fatty infiltration of the liver is therefore often diagnosed on CT and is important because it can be reversed. It can progress to end stage liver disease in a minority of cases if allowed to take its course. It is therefore important not to ignore it and consult with your physician. The underlying causative factor is important to identify. In some select cases, additional imaging with MRI may be indicated.