Steatosis: Understanding Your Pathology Report

by Stephanie Reid, MD FRCPC
December 21, 2025

Steatosis is a non-cancerous liver condition in which fat builds up inside liver cells, called hepatocytes. It is one of the main features of a group of conditions known as fatty liver disease. In steatosis, liver cells remain viable, but excess fat can interfere with liver function and, in some people, progress to more serious liver disease.

What causes steatosis?

Steatosis develops when too much fat reaches the liver or when the liver cannot process fat properly.

Under normal circumstances, dietary fat is absorbed in the intestine and transported through the bloodstream to various organs, including the liver. The liver plays a central role in fat metabolism. It takes in fatty acids, uses them for energy, stores small amounts when needed, or packages them into particles called lipoproteins to be sent back into the bloodstream and used by other tissues.

Steatosis occurs when this balance is disrupted. This can happen for several reasons:

• Too much fat arrives at the liver at once.

• The liver makes too much fat.

• The liver cannot efficiently break down fat.

• The liver cannot export fat effectively.

When any of these processes fail, fat accumulates within hepatocytes.

Common causes include alcohol use, which directly interferes with the liver’s ability to break down and export fat. Metabolic conditions, such as obesity, type 2 diabetes, and insulin resistance, increase the amount of fat delivered to the liver and promote fat production within liver cells. Dietary factors, especially diets high in sugars or unhealthy fats, can worsen this process.

Some medications can alter how the liver handles fat, leading to accumulation. Rare genetic or metabolic diseases, such as Wilson’s disease, can also impair normal fat metabolism.

In many people, steatosis develops because several factors act together, overwhelming the liver’s normal fat-processing capacity.

What symptoms can steatosis cause?

Most people with steatosis have no symptoms. The condition is often discovered incidentally during imaging tests, such as ultrasound or CT scans, performed for other reasons.

Some people may experience vague discomfort or dull pain in the right upper abdomen, where the liver is located. This pain is usually mild and not specific to steatosis.

If imaging shows fat in the liver, a liver biopsy may be performed to determine the type of fatty liver disease and to assess whether there is inflammation or scarring.

How is steatosis diagnosed?

Steatosis is diagnosed when a pathologist examines a liver biopsy under the microscope and sees fat droplets inside hepatocytes.

Normal hepatocytes do not contain visible fat droplets. In steatosis, the fat appears as clear spaces within the cells, pushing the cell contents aside. The diagnosis is based on the number of liver cells that contain these fat droplets.

How do pathologists grade steatosis?

Pathologists grade steatosis based on the percentage of hepatocytes that contain fat. This grading helps describe the extent of fat accumulation but does not, by itself, indicate inflammation or scarring.

• Mild steatosis: Fat is present in less than 33% of liver cells.

• Moderate steatosis: Fat is present in 33–66% of liver cells.

• Severe steatosis: Fat is present in more than 66% of liver cells.

Other information that may be included in your pathology report

In addition to grading steatosis, your pathology report may include several other findings that help doctors assess your liver health.

Adequacy

To make an accurate diagnosis, the biopsy must contain enough portal tracts, which are key structures that include a vein, an artery, and a bile duct. The report may state whether the sample is adequate or list the number of portal tracts examined.

Fragmentation

Liver tissue affected by disease can be fragile. If the biopsy breaks into multiple pieces, this may be described as fragmentation. While fragmentation does not change the diagnosis, it can be a clue to underlying liver scarring.

Ballooning hepatocytes

Ballooning refers to swollen, injured liver cells that appear much larger and paler than normal liver cells. Ballooning hepatocytes are not a feature of simple steatosis and are usually reported as absent. Their presence suggests a more severe form of fatty liver disease, such as steatohepatitis.

Inflammation

Inflammatory cells can enter different parts of the liver, including:

• The lobules, which contain hepatocytes.

• The portal tracts, which carry blood and bile.

• Areas around the central veins.

If inflammation is present, the pathologist describes its location, severity (mild, moderate, or severe), and the types of inflammatory cells seen. Inflammation is a key feature of steatohepatitis rather than simple steatosis.

Mallory bodies

Mallory bodies are clumps of damaged protein found inside injured hepatocytes. They are not seen in simple steatosis but may be present in more advanced liver diseases. Their presence helps pathologists narrow down the underlying cause of liver injury.

Fibrosis

Fibrosis is scar tissue that forms after repeated liver injury. Pathology reports often describe the stage of fibrosis, which reflects the extent and location of scarring.

As fibrosis increases, it can disrupt the normal liver structure. The most advanced stage of fibrosis is cirrhosis, where large bands of scar tissue divide the liver into nodules and significantly impair liver function.

Bile ducts

Each portal tract normally contains one bile duct. Some liver diseases damage or reduce the size of the bile ducts. For this reason, the pathologist examines bile ducts to ensure the normal number is present and that they appear healthy.

Cholestasis

Cholestasis means bile is trapped inside the liver instead of flowing normally into the intestine. Trapped bile can damage liver cells. If cholestasis is present, the report will describe where it is observed and its severity.

Iron

Excess iron can accumulate in the liver due to inherited conditions, repeated blood transfusions, or impaired liver function. Iron may be found inside hepatocytes or immune cells called macrophages. If present, its location and severity are described because iron can contribute to liver damage.

Questions to ask your doctor

• Do I have mild, moderate, or severe steatosis?
• Is there any inflammation or scarring in my liver?
• Could my steatosis progress to a more serious condition?
• What changes can I make to reduce fat in my liver?
• Do I need follow-up imaging or another biopsy?