Hepatic steatosis, also known as fatty liver disease, refers to abnormal accumulation of fat within hepatocytes, most commonly manifesting as non-alcoholic fatty liver disease (NAFLD). It represents a spectrum from simple steatosis to steatohepatitis and cirrhosis, frequently identified incidentally on imaging 1215.

Hepatic steatosis affects up to 30% of the general population in Western countries, with rising prevalence linked to obesity, diabetes, and metabolic syndrome. Prevalence exceeds 70% in patients with type 2 diabetes and reaches 90% in those undergoing bariatric surgery. Risk factors include insulin resistance, hyperlipidemia, rapid weight loss, total parenteral nutrition, and certain medications 1517.

Most cases remain asymptomatic and are detected incidentally on ultrasound or other imaging. Symptomatic patients may report right upper quadrant discomfort, fatigue, or elevated liver enzymes. Advanced disease can progress to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis, or hepatocellular carcinoma 1618.

Steatosis results from impaired fat metabolism, with triglycerides accumulating in >5% of hepatocytes. Macrovesicular steatosis predominates, featuring a single large cytoplasmic fat droplet displacing the nucleus; microvesicular involves multiple small droplets. Focal forms occur due to variant venous drainage, while diffuse patterns predominate 1321.

* Hyperechoic liver parenchyma (”bright liver”) compared to kidney or spleen * Grading:

Advanced techniques quantify via attenuation imaging or backscatter coefficient 14.

* Unenhanced CT: Liver attenuation <40 HU absolute or >10 HU lower than spleen (sensitivity ~80% for moderate-severe steatosis) * Contrast-enhanced: Focal sparing appears hyperdense relative to steatotic parenchyma (gallbladder fossa, segment IV) * Dual-energy CT improves quantification 1215.

* Chemical shift imaging (in/out-of-phase): Signal dropout on opposed-phase images (>5% fat) * Proton density fat fraction (PDFF): Gold standard for quantification (linear, reproducible) * Spectroscopy: Measures fat fraction directly 1517.

Management targets underlying causes (weight loss, diabetes control). Steatosis alone carries excellent prognosis without fibrosis; NASH risks progression to cirrhosis (20-30%). Surveillance recommended for advanced fibrosis 1619.

* Glycogen storage disease (US: hyperechoic but vessels clear) * Acute hepatitis (diffuse hypoechoic) * Focal fat sparing/deposition mimics mass * Iron overload (high attenuation on CT) 1321