====== Liver steatosis ======

**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)**.

===== Epidemiology =====
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.

===== Clinical presentation =====
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.

===== Pathology =====
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.

===== Radiographic features =====

==== Ultrasonography ====

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

^ Grade     ^ Features                                      ^
| Mild      | Slight echogenicity increase                   |
| Moderate  | Impaired vessel wall visualization             |
| Severe    | Poor diaphragm/portal vein visibility          |

==== Computed tomography ====

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

==== Magnetic resonance imaging ====

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

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

===== Differential diagnosis =====

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

===== References =====
* [[https://pubs.rsna.org/doi/full/10.1148/rg.266065004|RadioGraphics 2006: Fatty Liver]]
* [[https://pmc.ncbi.nlm.nih.gov/articles/PMC6824276/|Ultrasound Med 2019]]
* [[https://ajronline.org/doi/10.2214/AJR.11.7838|AJR Am J Roentgenol 2012]]
* [[https://pubs.rsna.org/doi/full/10.1148/radiol.2021204288|Radiology 2021]]
* [[https://pmc.ncbi.nlm.nih.gov/articles/PMC4064084/|World J Gastroenterol 2014]]
* [[https://www.sciencedirect.com/science/article/abs/pii/S0720048X06004451|Eur J Radiol 2007]]

> **Medical Disclaimer**: Portions of this content were AI-generated to facilitate rapid knowledge synthesis. Radiologists and clinicians must independently verify all information against peer-reviewed literature, institutional protocols, and patient-specific factors before clinical application.