Liver ultrasound is a valuable diagnostic tool for assessing liver anatomy, size, and pathology. It is a non-invasive, painless, and relatively quick procedure that does not involve exposure to ionizing radiation.
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Indications
Liver ultrasound is commonly utilized in the evaluation of various hepatic conditions. The most frequent indications include 1,2:
screening for hepatic disease in at-risk populations (e.g. hepatocellular cancer screening in cirrhotic patients)
investigation of abnormal liver function tests
evaluation of focal liver lesions detected on other imaging modalities
assessment of liver size in patients with suspected hepatomegaly
monitoring chronic liver disease
assessment of portal venous system and bile ducts in patients with possible obstruction
guiding biopsies or therapeutic interventions
Technique
Before conducting a liver ultrasound examination, the patient should ideally fast for at least 6 hours to minimize bowel gas interference. The examination consists of grayscale B-mode imaging complemented by Doppler studies if necessary. To optimize image quality and facilitate accurate assessment of the entire liver, use proper gain settings and probe manipulation is crucial.
Normal findings
Anatomic structures that are expected to be visualized during routine liver ultrasound include the right/left lobes of the liver, caudate lobe, intrahepatic blood vessels (portal, hepatic veins), gallbladder, and extrahepatic bile ducts.
Common findings of a normal ultrasound examination should include 2,3:
homogeneous parenchymal echogenicity
smooth capsule with a regular contour
normal size of liver lobes: right lobe measuring 13-15 cm in craniocaudal dimension, and left lobe measuring <7 cm in width
patent intrahepatic vasculature with no evidence of thrombosis or dilatation
gallbladder free of stones and normal wall thickness (<3 mm)
common bile duct measuring <6 mm in diameter
Pathological findings
Some common pathologies and abnormal findings that could be detected during liver ultrasound examination are:
focal liver lesions, e.g. cysts, hemangiomas, metastases, hepatocellular carcinoma
diffuse liver diseases, e.g. fatty infiltration, cirrhosis, hepatitis
biliary diseases, e.g. gallstones, cholecystitis
vascular abnormalities, e.g. portal hypertension, portal vein thrombosis
Practical points
Some potential pitfalls and challenges that encounter during liver ultrasound include 3,4:
technical factors: such as shadowing artifacts from bowel gas or inappropriate gain settings
anatomic variations: e.g., accessory lobes or fissures that may mimic focal lesions
atypical appearances of benign hepatic lesions: e.g., complicated cysts or focal fatty sparing/replacement
small or isoechoic malignancies that may not be well visualized within the background parenchyma