Common Ultrasound Findings in Hepatobiliary Disorders

Common Ultrasound Findings in Hepatobiliary Disorders

I. Introduction

Hepatobiliary disorders encompass a wide spectrum of conditions affecting the liver, gallbladder, and bile ducts, ranging from common benign entities like gallstones to life-threatening malignancies such as hepatocellular carcinoma. In Hong Kong, liver diseases are a significant public health concern. According to the Hong Kong Cancer Registry, liver cancer was the fourth most common cancer and the third leading cause of cancer deaths in 2021. Furthermore, non-alcoholic fatty liver disease (NAFLD) is estimated to affect approximately 27-30% of the adult population in Hong Kong, mirroring global trends linked to metabolic syndrome. The timely and accurate diagnosis of these conditions is paramount for effective patient management. Among the various imaging modalities available, ultrasound stands as the cornerstone of initial evaluation for hepatobiliary complaints. Its widespread availability, non-invasive nature, lack of ionizing radiation, and real-time imaging capabilities make it an indispensable first-line tool. The ultrasound hepatobiliary system examination provides a comprehensive assessment, evaluating parenchymal texture, vascular flow, biliary tree caliber, and gallbladder morphology. While advanced imaging like a thoracic spine MRI is crucial for evaluating metastatic spread from primary hepatobiliary cancers to the vertebral column, ultrasound remains the primary workhorse for characterizing the primary abdominal pathology itself. This article will delve into the characteristic sonographic appearances of common hepatobiliary disorders, providing a detailed guide for interpretation.

II. Liver Disorders

Ultrasound is exceptionally sensitive in detecting diffuse and focal liver pathologies. The examination begins with an assessment of parenchymal echogenicity, size, contour, and vascular patency.

A. Fatty Liver (Steatosis)

Hepatic steatosis, or fatty liver, is characterized by the abnormal accumulation of triglycerides within hepatocytes. On ultrasound, the hallmark finding is increased parenchymal echogenicity, often described as a "bright liver." This increased echogenicity results in poor penetration of sound waves, leading to posterior attenuation or decreased visualization of deeper structures, such as the diaphragm and the posterior portions of the liver. The hepatic vessels may appear less distinct due to the increased background echogenicity. Fatty liver is typically graded subjectively:

• Grade I (Mild): Slight, diffuse increase in hepatic echogenicity with normal visualization of the diaphragm and intrahepatic vessel borders.
• Grade II (Moderate): Moderate increase in echogenicity with slightly impaired visualization of the diaphragm and intrahepatic vessels.
• Grade III (Severe): Marked increase in echogenicity with poor penetration and significant posterior attenuation, obscuring the diaphragm and the posterior aspects of the right lobe.

It is crucial to note that ultrasound can detect macrovesicular steatosis but is less sensitive for mild steatosis (less than 20-30% fat infiltration). The pattern can be diffuse or focal, and focal fatty sparing—areas of normal liver parenchyma within a fatty liver—must be distinguished from masses. Correlation with clinical history (alcohol use, diabetes, obesity) and liver function tests is essential. In complex cases where atypical focal sparing raises concern, further evaluation with contrast-enhanced CT or MRI may be warranted to exclude underlying malignancy.

B. Cirrhosis

Cirrhosis represents the end-stage of chronic liver injury, characterized by fibrosis, regenerative nodules, and architectural distortion. The ultrasound findings evolve with the disease stage. Early cirrhosis may show only subtle coarsening of the parenchymal echo texture. Advanced cirrhosis demonstrates a nodular liver surface, best appreciated with a high-frequency linear transducer. The parenchyma becomes heterogeneous and coarse. Portal hypertension, a major complication, manifests with several key findings:

• Splenomegaly: A spleen length exceeding 13 cm is a common indicator.
• Ascites: Free fluid appears as anechoic (black) areas in the peritoneal spaces, most commonly in the hepatorenal recess (Morison's pouch) and pelvis.
• Portosystemic Collaterals: Recanalization of the paraumbilical vein or development of gastric varices can be visualized.

Doppler ultrasound is critical in assessing portal hypertension. Findings may include decreased or hepatofugal (away from the liver) flow in the main portal vein, increased arterial flow in the hepatic artery as a compensatory mechanism, and loss of phasicity in the hepatic veins due to parenchymal stiffness. While ultrasound is excellent for monitoring these complications, a patient with suspected metastatic disease from hepatocellular carcinoma may require a thoracic spine MRI to evaluate for vertebral body involvement, a common site for hematogenous spread.

C. Liver Masses

Characterizing liver masses is a primary strength of the ultrasound hepatobiliary system exam. The approach focuses on distinguishing benign from malignant lesions.

• Cysts: Simple hepatic cysts are common, benign lesions with classic features: anechoic (fluid-filled) content, smooth, thin walls, and posterior acoustic enhancement (increased through-transmission). Complex cysts may have internal echoes, septations, or wall thickening, raising concern for infection or neoplasm (e.g., cystadenoma).
• Hemangiomas: The most common benign liver tumor. Typical appearance is a well-defined, hyperechoic mass with posterior acoustic enhancement. Larger hemangiomas can be heterogeneous. On color Doppler, they often show peripheral nodular enhancement with slow fill-in, though this is better assessed with contrast-enhanced ultrasound (CEUS) or MRI.
• Hepatocellular Carcinoma (HCC): In a cirrhotic liver, any new solid mass is suspicious for HCC. Sonographic features vary but often include a hypoechoic or mixed echogenicity mass, a "mosaic" pattern, a peripheral hypoechoic halo (representing a fibrous capsule), and internal vascularity on Doppler. The "wash-in, wash-out" pattern on CEUS or contrast CT/MRI is diagnostic.
• Metastases: Appearances are protean and often reflect the primary tumor. Common patterns include multiple hypoechoic ("bull's eye" or target) lesions, hyperechoic lesions (from GI tract or vascular primaries), or calcified metastases (e.g., from mucinous colorectal cancer). A diffusely infiltrative pattern can also occur.

Ultrasound serves as an excellent screening and surveillance tool, guiding the need for biopsy or definitive cross-sectional imaging.

III. Gallbladder Disorders

The gallbladder is ideally suited for sonographic evaluation due to its fluid content.

A. Cholelithiasis (Gallstones)

Gallstones are highly echogenic foci within the gallbladder lumen. The key diagnostic feature is posterior acoustic shadowing—a clean, anechoic (black) band behind the stone caused by near-total reflection of sound waves. Stones are typically mobile with changes in patient position. Complications include:

• Acute Cholecystitis: Inflammation due to cystic duct obstruction by a stone.
• Choledocholithiasis: Passage of a stone into the common bile duct, causing potential obstruction and jaundice.
• Gallstone Ileus: A rare complication where a large stone erodes through the gallbladder wall into the bowel, causing obstruction.

Sludge (echogenic, layering bile without shadowing) is a common finding and can be a precursor to stone formation.

B. Cholecystitis

Acute calculous cholecystitis is diagnosed by a combination of sonographic signs. Primary findings include:

• Gallstones: Usually impacted in the gallbladder neck or cystic duct.
• Gallbladder Wall Thickening: >3 mm. However, this is non-specific and can be seen in other conditions like hepatitis, ascites, or heart failure.
• Pericholecystic Fluid: Anechoic fluid surrounding the gallbladder, indicating inflammation and possible perforation.
• Sonographic Murphy's Sign: Maximal tenderness when the ultrasound probe is pressed directly over the visualized gallbladder. This is a highly specific sign when present.

Secondary signs include gallbladder distension (short-axis diameter >4 cm) and increased vascularity in the wall on color Doppler. Acalculous cholecystitis, often seen in critically ill patients, shows wall thickening, sludge, and distension without stones.

C. Gallbladder Polyps

Gallbladder polyps are mucosal projections into the lumen. On ultrasound, they appear as non-mobile, non-shadowing, soft tissue echogenic structures attached to the wall. They do not move with gravity, unlike stones. The vast majority are cholesterol polyps, which are benign. Management is based on size and morphology:

Features suggestive of a malignant polyp include size >10 mm, solitary, sessile shape, rapid growth, and associated wall thickening. Differentiation from an adherent stone or tumefactive sludge is crucial.

IV. Bile Duct Disorders

Evaluation of the biliary tree is a critical component of the ultrasound hepatobiliary system exam, focusing on ductal caliber and content.

A. Choledocholithiasis (Common Bile Duct Stones)

Stones in the common bile duct (CBD) are a common cause of obstructive jaundice. Ultrasound findings include:

• Dilated Bile Ducts: A CBD diameter >7 mm (or >10 mm post-cholecystectomy) is suggestive of obstruction. Intrahepatic duct dilation appears as "too many tubes" or a "stellate" pattern at the porta hepatis.
• Echogenic Foci with Shadowing: Visualizing the actual stone in the CBD can be challenging due to overlying bowel gas. The stone appears as an echogenic focus within the dilated duct, often with a clear posterior acoustic shadow. The distal CBD is a common site and may require patient positioning (left lateral decubitus) for optimal visualization.

Sensitivity of transabdominal ultrasound for CBD stones is moderate (~50-75%), and if clinical suspicion remains high despite a negative ultrasound, endoscopic ultrasound (EUS) or MRCP is indicated.

B. Cholangitis

Cholangitis is a bacterial infection of the biliary tree, often secondary to obstruction (e.g., by a stone or stricture). Ultrasound findings may include:

• Bile Duct Dilation: As described above.
• Bile Duct Wall Thickening: Irregular or smooth thickening of the duct walls.
• Sludge or Pus: Low-level echoes within the dilated ducts, representing infected bile.
• Underlying Cause: Identification of a stone, stricture, or mass causing the obstruction.

Clinical presentation (Charcot's triad: fever, jaundice, right upper quadrant pain) is paramount for diagnosis, as ultrasound findings can be subtle in early stages.

C. Biliary Strictures

Strictures are abnormal narrowings of the bile ducts. Causes can be benign (post-surgical, inflammatory, primary sclerosing cholangitis - PSC) or malignant (cholangiocarcinoma, pancreatic head carcinoma). Ultrasound findings include:

• Dilation Upstream (Proximal) to the Stricture: Abrupt caliber change from dilated to normal or narrowed duct.
• Wall Abnormalities: Focal wall thickening or a mass lesion at the site of narrowing.
• PSC: Characteristic findings include multifocal, short-segment strictures with mild dilation, creating a "beaded" appearance. The wall is often thickened and hyperechoic.

While ultrasound can suggest a stricture and its level, definitive characterization often requires MRCP, ERCP, or percutaneous cholangiography. For a patient with cholangiocarcinoma, staging may involve a thoracic spine MRI to rule out distant metastatic disease.

V. Case Studies

To integrate the findings discussed, consider these illustrative, anonymized cases based on typical presentations in a Hong Kong radiology department.

Case 1: A 55-year-old man with a history of Hepatitis B and cirrhosis presents for surveillance ultrasound. The ultrasound hepatobiliary system exam reveals a coarse, nodular liver contour, splenomegaly (14 cm), and a small amount of ascites. A new 2.5 cm hypoechoic mass with a peripheral halo is identified in segment VI. Color Doppler shows internal vascularity. Diagnosis: High suspicion for Hepatocellular Carcinoma (HCC) in a cirrhotic liver. The patient was referred for contrast-enhanced MRI for confirmation and staging.

Case 2: A 40-year-old woman presents with acute right upper quadrant pain and fever. Ultrasound shows a distended gallbladder with a 1 cm echogenic stone impacted in the neck, casting a strong acoustic shadow. The gallbladder wall is thickened to 5 mm, and pericholecystic fluid is present. Sonographic Murphy's sign is positive. Diagnosis: Acute Calculous Cholecystitis. The patient underwent laparoscopic cholecystectomy.

Case 3: A 70-year-old man with painless jaundice and weight loss. Ultrasound reveals marked intra- and extrahepatic biliary dilation. The CBD measures 15 mm. At the distal CBD/pancreatic head region, an ill-defined, hypoechoic mass is seen causing abrupt termination of the duct. No shadowing stone is identified. Diagnosis: Obstructive jaundice secondary to a periampullary/pancreatic head mass, highly suspicious for malignancy. Further workup with CT and ERCP was arranged. As part of the metastatic workup for pancreatic cancer, imaging of the axial skeleton, potentially including a thoracic spine MRI, would be considered.

VI. Conclusion

Ultrasound remains the primary, non-invasive imaging modality for the initial assessment of hepatobiliary disorders. Its ability to characterize parenchymal texture, identify stones, visualize masses, and assess vascular flow makes it invaluable. The findings discussed—from the bright liver of steatosis and the nodularity of cirrhosis to the shadowing of gallstones and the dilation of obstructed bile ducts—form the foundational language of hepatobiliary sonography. However, the interpretation of these findings must never occur in a vacuum. The sonographer and radiologist must meticulously correlate the ultrasound images with the patient's clinical history, laboratory values (especially liver function tests and tumor markers), and risk factors. An ultrasound suggesting metastatic liver disease should prompt a search for a primary tumor and appropriate staging investigations. Similarly, a diagnosis of HCC in a cirrhotic patient necessitates a comprehensive staging approach. Ultimately, the ultrasound hepatobiliary system examination is a powerful diagnostic tool, and its judicious use, combined with clinical correlation and knowledge of its limitations, is essential for optimal patient care and guiding further management pathways.