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).

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.

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.

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.

• Hyperechoic liver parenchyma (”bright liver”) compared to kidney or spleen ¹⁾
• Grading:

• Unenhanced CT: Liver attenuation <40 HU absolute or >10 HU lower than spleen ²⁾
• Contrast-enhanced: Focal sparing appears hyperdense relative to steatotic parenchyma (gallbladder fossa, segment IV) ³⁾
• Dual-energy CT improves quantification ⁴⁾

• Chemical shift imaging (in/out-of-phase): Signal dropout on opposed-phase images (>5% fat) ⁵⁾
• Proton density fat fraction (PDFF): Gold standard for quantification ⁶⁾
• Spectroscopy: Measures fat fraction directly

Management targets underlying causes (weight loss, diabetes control). Steatosis alone carries excellent prognosis without fibrosis; NASH risks progression to cirrhosis (20-30%) ⁷⁾.

• Glycogen storage disease (US: hyperechoic but vessels clear) ⁸⁾
• Acute hepatitis (diffuse hypoechoic) ⁹⁾
• Focal fat sparing/deposition mimics mass ¹⁰⁾
• Iron overload (high attenuation on CT) ¹¹⁾

* ¹²⁾ RadioGraphics 2006: Fatty Liver * ¹³⁾ [[https://pmc.ncbi.nlm.nih.gov/articles/PMC6824276/|Ultrasound Med 20