A liver ultrasound is a non-invasive medical imaging procedure that uses high-frequency sound waves to create real-time pictures of the liver and surrounding structures. This procedure is painless and does not involve ionizing radiation, making it a safe option for investigating various abdominal concerns. Doctors often order this test to check for the source of upper abdominal pain, investigate abnormal liver function tests, or screen for chronic liver disease, such as cirrhosis or fatty liver disease. The resulting images provide detailed information about the organ’s size, texture, and any structural abnormalities.
How Ultrasound Images Are Formed
The process of forming an ultrasound image begins when a handheld device, called a transducer, is placed on the skin. The transducer emits sound waves into the body, which travel through soft tissues until they encounter an interface between different materials. At these interfaces, some sound waves are reflected back to the transducer as echoes.
The ability of a structure to reflect these sound waves is termed echogenicity, which determines the brightness of the structure on the final image. Structures reflecting many sound waves appear brighter, while those reflecting few appear darker. The ultrasound machine processes the timing and strength of these returning echoes to map out a two-dimensional, grayscale image.
The visual language of ultrasound uses three primary terms to describe brightness. Anechoic structures (like fluid-filled cysts) appear completely black, reflecting virtually no sound waves. Hyperechoic structures (like calcifications) appear bright white due to reflecting a large number of echoes. Hypoechoic structures reflect fewer sound waves than surrounding tissue, appearing as shades of dark gray.
The consistency of the tissue is described by its texture. Homogeneous refers to a uniform, even appearance, while heterogeneous describes a mixed or non-uniform texture.
Visualizing the Healthy Liver
A healthy liver establishes the baseline for interpretation. It is recognized by characteristic visual features, including a smooth, regular contour and sharp edges. Size is typically measured in the right lobe, usually under 15 to 16 centimeters in the largest dimension.
The main body of the liver tissue, known as the parenchyma, should present as uniformly homogeneous in texture. Its echogenicity is typically medium density, often appearing slightly brighter than the adjacent renal cortex of the right kidney.
Internal structures provide important reference points. Portal vein walls are typically hyperechoic (bright), making them easily visible within the darker parenchyma. Hepatic veins, which drain blood out, have thin walls and often appear less prominent. The nearby gallbladder should be free of stones and have a thin, smooth wall.
Distinguishing Common Liver Findings
Understanding the language of echogenicity allows for the distinction of common findings.
Fatty Liver Disease (Steatosis)
Fatty liver disease, or steatosis, is characterized by a diffuse increase in the liver’s echogenicity, making the entire organ appear brighter than the normal baseline. The presence of fat scatters the sound waves, resulting in the liver appearing hyperechoic compared to the adjacent kidney. This increased echogenicity leads to poor penetration of sound waves, a phenomenon called acoustic attenuation. This attenuation causes deeper parts of the liver, the diaphragm, and the hepatic veins to appear less clear or obscured.
Simple Hepatic Cysts
Simple hepatic cysts are common, benign findings recognized as perfectly anechoic (black) structures. These fluid-filled sacs have sharp, smooth walls and are typically spherical or oval. Because sound travels easily through the fluid, the tissue immediately behind the cyst often appears brighter than the surrounding parenchyma, an effect known as posterior acoustic enhancement.
Hemangiomas
Hemangiomas are benign masses composed of blood vessels, usually seen as well-defined, homogeneous hyperechoic masses. High reflection of sound waves results in a distinctly bright appearance. These masses are typically small (under 3 centimeters) and have sharp margins.
Gallstones
Gallstones appear as intensely bright, highly hyperechoic spots, usually within the gallbladder. Their density completely blocks sound waves, creating a distinct posterior acoustic shadowing. This shadow is a dark, anechoic band extending directly behind the stone, confirming the diagnosis of cholelithiasis.
Interpreting the Final Report
The final written report is created by the radiologist to communicate findings to the ordering physician. The report is divided into sections, beginning with the “Findings.” This section details the technical observations made during the scan, describing the liver size, parenchyma echogenicity, and visual characteristics of any observed structures.
Following the detailed observations is the “Impression” or “Conclusion.” This section represents the radiologist’s summarized interpretation and diagnostic assessment. It translates the technical findings into a concise statement about the most significant observations, often including a potential diagnosis or a recommendation for further action.
Common jargon can be demystified to aid understanding. The term “unremarkable” or “no acute findings” means the structures appeared within normal limits. Terms like “complex cyst” or “follow-up recommended” indicate that the finding requires further clinical correlation or repeat imaging. It is important to discuss the Impression and any recommendations directly with the physician who ordered the test.