What is Hepatic Steatosis?
Hepatic steatosis is the accumulation of excess fat (specifically triacylglycerols) in the liver, defined as intrahepatic fat comprising at least 5% of liver weight, visible as lipid droplets within hepatocytes. 1, 2
Core Definition and Pathophysiology
Hepatic steatosis represents abnormal lipid accumulation in liver cells that occurs when there is an imbalance between fatty acid delivery/synthesis and disposal through oxidation or secretion. 2, 3 The condition requires:
- Evidence of fat accumulation either by imaging (ultrasound showing increased liver echogenicity) or histology 1, 4
- Exclusion of secondary causes such as significant alcohol consumption, steatogenic medications, or hereditary disorders 1
The fat accumulation results from increased fatty acid flux to the liver, increased de novo lipogenesis, and/or reduced clearance through β-oxidation or very-low-density lipoprotein secretion. 2
Clinical Spectrum and Classification
Hepatic steatosis exists on a spectrum from simple fat accumulation to progressive inflammatory disease:
- Simple steatosis (70-75% of cases): Fat accumulation without hepatocyte injury or inflammation, which typically remains benign and non-progressive 4, 5
- Steatohepatitis (25-30% of cases): Fat accumulation plus hepatocyte injury (ballooning) and inflammation, which can progress to fibrosis, cirrhosis, and hepatocellular carcinoma 1, 4
The current terminology has evolved to Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), defined as hepatic steatosis plus at least one cardiometabolic risk factor (obesity, type 2 diabetes, dyslipidemia). 6, 7
Prevalence and Risk Factors
- General population prevalence: 20-30% globally, affecting approximately 30% of the world's population 4, 7
- High-risk populations: 70% in obesity and 90% in type 2 diabetes 4
- Primary associations: Obesity, type 2 diabetes, dyslipidemia, and metabolic syndrome 1, 2
Diagnostic Approach
Ultrasound serves as the first-line diagnostic tool, showing increased liver echogenicity compared to renal cortex, with 84.8% sensitivity and 93.6% specificity for moderate to severe hepatic fat deposition. 4 The hepatorenal index provides more objective evaluation, with grading as mild, moderate, or severe. 4
Clinical Presentation
A critical caveat: 60-80% of patients with chronic hepatic steatosis are completely asymptomatic. 5 When symptoms occur, they are nonspecific and include abdominal discomfort, fatigue, nausea, and muscle pain. 5 The liver capsule lacks pain receptors for stretch or fat accumulation alone—pain typically requires inflammation (steatohepatitis), rapid enlargement, or complications like cirrhosis. 5
Prognostic Implications
The presence and progression of liver fibrosis driven by hepatic inflammation is the main predictor of liver-related death across the spectrum of steatotic liver diseases. 7 Patients with simple steatosis have very slow, if any, histological progression, while those with steatohepatitis can progress to cirrhotic-stage disease. 1 Steatotic liver disease has become the leading cause of cirrhosis in the EU and USA. 7