The liver ultrasound is a non-invasive imaging procedure that uses high-frequency sound waves to create real-time pictures of the liver and surrounding structures. A handheld device called a transducer is placed on the abdomen, which emits sound waves and records the echoes that bounce back from the tissues. These returning sound waves are converted into a visual image on a monitor, allowing physicians to assess the organ’s size, shape, and internal texture. Because it does not use ionizing radiation and is widely available, ultrasound often serves as the initial screening tool for evaluating liver health and investigating symptoms like unexplained abdominal discomfort or abnormal blood tests.
Visualizing Overall Organ Health and Texture
The primary function of a liver ultrasound is to assess the overall condition of the liver tissue, known as the parenchyma, looking for changes that affect the entire organ diffusely. One common finding is hepatic steatosis, or fatty liver disease, identified by an increase in the liver’s echogenicity. This means the liver tissue appears brighter or “whiter” on the screen, caused by fat droplets scattering the sound waves more intensely than normal tissue.
The degree of echogenicity is qualitatively graded as mild, moderate, or severe by comparing the liver’s brightness to the adjacent renal cortex. In pronounced cases of fat accumulation, sound waves are attenuated, leading to poor visualization of deeper structures, such as the walls of the hepatic and portal veins. The ultrasound also helps determine if the liver is enlarged, a condition called hepatomegaly, which can be a sign of various underlying issues, including inflammation or heart failure.
The scan is instrumental in detecting signs of long-term damage like fibrosis or cirrhosis, which involve the buildup of scar tissue. A cirrhotic liver typically shows an abnormally coarse or heterogeneous texture and an irregular, lumpy surface contour. As the disease progresses, the liver’s shape can change, often becoming shrunken, though the caudate lobe may appear enlarged. These diffuse changes indicate chronic disease and provide information about the severity of the liver damage.
Identifying Focal Abnormalities and Masses
In addition to diffuse disease, the liver ultrasound is highly effective at identifying specific, localized findings, often referred to as focal lesions or masses. These abnormalities are distinct areas within the liver tissue that differ in appearance from the surrounding parenchyma. Hepatic cysts are among the most frequent incidental findings; they are simple, fluid-filled sacs that appear characteristically anechoic (black on the image). Simple cysts have well-defined, thin walls and often demonstrate posterior acoustic enhancement, appearing as a bright area behind the cyst because sound waves travel easily through the fluid.
Solid masses, composed of tissue rather than fluid, can also be detected and partially characterized. Benign masses like hemangiomas, which are tangled collections of blood vessels, typically appear very bright or hyperechoic on the scan. Another benign lesion, focal nodular hyperplasia (FNH), may present with a variable appearance, sometimes showing a characteristic “spoke-wheel” pattern when Doppler technology is applied.
The ultrasound serves as a screening tool for potentially malignant tumors, such as hepatocellular carcinoma (HCC) or metastatic lesions, which can appear as solid, hypoechoic (darker) masses. However, ultrasound alone cannot definitively distinguish between all benign and malignant solid masses due to their varied appearances. If a complex cyst (with features like thick walls or internal septations) or a suspicious solid mass is detected, additional cross-sectional imaging like a CT or MRI scan is recommended for a more precise diagnosis. The scan can also identify pockets of infection, known as abscesses, which usually present as heterogeneous or hypoechoic areas lacking internal blood flow.
Assessing Vascular Flow and the Biliary System
A specialized application, Doppler ultrasound, evaluates the flow of blood through the liver’s extensive network of vessels. This technique measures the speed and direction of blood flow, providing information about the patency of vessels like the hepatic veins and the portal vein. Assessing the portal vein is important for diagnosing portal hypertension, a complication of chronic liver disease where blood flow resistance is increased.
Signs of portal hypertension on Doppler include an enlarged portal vein diameter, decreased blood flow velocity, or even a reversed flow direction. The Doppler assessment is used to check for thrombosis, or blood clots, within the portal or hepatic veins. Separately, the ultrasound provides excellent visualization of the biliary system, the network of ducts that drain bile from the liver.
The scan can detect if the bile ducts are abnormally dilated, which indicates an obstruction caused by a stone, stricture, or mass blocking the normal flow of bile. The diameter of the common bile duct, which should not typically exceed 6 millimeters in a healthy adult, is a key measurement. Because the gallbladder is closely associated with the liver and biliary system, ultrasound is the primary tool for its evaluation. The scan accurately identifies gallstones (cholelithiasis), which appear as bright, reflective objects that cast a shadow, and can detect signs of inflammation, such as thickening of the gallbladder wall.