Fatty liver disease, also known as hepatic steatosis, is a condition where excess fat accumulates in the liver. This can interfere with the liver’s functions, such as digesting food, storing energy, and removing toxins. Ultrasound, a non-invasive imaging technique, is frequently used to identify this condition.
Understanding Fatty Liver
Fatty liver disease occurs when fat makes up more than 5-10% of the liver’s weight. This accumulation can lead to inflammation and damage of liver cells, a more severe form called steatohepatitis. If left unaddressed, steatohepatitis can progress to fibrosis, which involves scarring of the liver, and potentially advance to cirrhosis, leading to liver failure or liver cancer.
The prevalence of fatty liver disease is increasing globally, affecting approximately 25-30% of the general population. It is the most common chronic liver disorder in Western countries. While various factors contribute to fat accumulation, it is often seen in individuals who are overweight or obese, have type 2 diabetes, or high levels of fats like cholesterol and triglycerides in their blood.
How Ultrasound Detects Fatty Liver
Ultrasound imaging uses high-frequency sound waves transmitted into the body by a probe. These waves reflect off tissues as echoes, which are converted into real-time images on a screen.
Fat within liver cells alters how sound waves interact with the tissue. Normally, the liver’s echogenicity, or brightness on the ultrasound image, is similar to or slightly more echogenic than the adjacent kidney. However, fat accumulation causes increased scattering of sound waves, resulting in a brighter appearance of the liver parenchyma, known as increased echogenicity or hyperechogenicity. This phenomenon is often referred to as a “bright liver.”
Beyond increased brightness, fatty infiltration also leads to increased attenuation of the ultrasound beam. This means sound waves lose energy as they travel through fatty tissue, resulting in poorer visualization of deeper structures. This reduced penetration makes it harder to see the borders of intrahepatic vessels (blood vessels within the liver) and the diaphragm, which is the muscular wall separating the chest and abdomen.
Interpreting Ultrasound Findings
Radiologists look for specific visual characteristics on ultrasound images to diagnose fatty liver. A common indicator is diffuse hyperechogenicity, where the entire liver appears uniformly brighter than normal. This brightness is often compared to the right kidney, with a fatty liver appearing significantly brighter than the kidney’s cortex.
Another sign is impaired visualization of deep liver structures. Due to attenuation by accumulated fat, the normal echogenic walls of the portal and hepatic veins may appear blurred or not visible. Similarly, the diaphragm, which should be clearly distinguishable behind the liver, might be poorly visualized or completely obscured in more advanced cases.
Based on these visual cues, a subjective grading system assesses severity. In mild cases, there is a diffuse increase in liver echogenicity, but periportal echogenicity and the diaphragm are still clearly visible. Moderate fatty liver shows a more pronounced increase in echogenicity, obscuring periportal echogenicity, though the diaphragm may still be discernible. In severe fatty liver, there is a marked increase in liver brightness, with poor or no visualization of intrahepatic vessel borders, the diaphragm, and the posterior segments of the right lobe of the liver.
What to Expect After an Ultrasound Diagnosis
Receiving a fatty liver diagnosis from an ultrasound often serves as an initial screening result. While ultrasound is effective in detecting fat, further evaluation is usually recommended to determine the specific type and severity, and to rule out other liver diseases. This may involve additional blood tests or specialized imaging like a FibroScan, which measures liver stiffness to assess for fibrosis.
In some situations, a liver biopsy might be suggested for a more definitive diagnosis and staging, though this is less common due to its invasive nature. Management primarily focuses on lifestyle modifications. Doctors recommend adopting a healthy diet, emphasizing fruits, vegetables, and lean proteins, while limiting fats and sugars. Regular physical activity and weight loss are also advised, as losing even 5-10% of body weight can reduce liver fat and improve the condition.
Patients are advised to limit or avoid alcohol consumption to reduce further stress on the liver. Ongoing medical follow-up is important to monitor liver function and assess for any disease progression. This may include periodic ultrasounds or other tests to track changes and address associated health conditions like diabetes, high blood pressure, or high cholesterol.