What is the significance of a starry sky appearance of the liver on ultrasound in a patient, potentially indicating liver disease such as fatty liver disease or cirrhosis?

Starry Sky Appearance of the Liver on Ultrasound

The "starry sky" appearance on liver ultrasound most commonly indicates biliary hamartomas (von Meyenburg complexes), which are benign developmental malformations requiring no treatment or follow-up, though this pattern can also indicate acute hepatic inflammation or congestion in specific clinical contexts. 1

Primary Diagnosis: Biliary Hamartomas

The term "starry sky" appearance specifically refers to innumerable small T2 hyperintense cystic lesions (2-10 mm) scattered throughout the hepatic parenchyma that create a characteristic pattern resembling stars in the night sky. 1 This finding is pathognomonic for biliary hamartomas when seen on MRI, though the term is sometimes loosely applied to other ultrasound patterns. 1

Key Imaging Characteristics of Biliary Hamartomas:

• Size: Typically 2-10 mm lesions distributed throughout the liver parenchyma 1
• Ultrasound appearance: May be hypoechoic, hyperechoic, or mixed heterogenic echoic structures with multiple "comet-tail" artifacts 1
• MRI confirmation: Shows markedly high intensity on T2-weighted sequences with well-defined margins, creating the classic "starry sky" pattern 1
• No communication with biliary tree: MR cholangiography confirms absence of connection to bile ducts, distinguishing this from Caroli disease 1

Clinical Management:

No follow-up imaging is recommended for asymptomatic patients with biliary hamartomas, as these are benign developmental lesions with no malignant potential. 1 This represents a strong recommendation with 96% consensus from the European Association for the Study of the Liver. 1

Alternative Diagnosis: Acute Hepatic Inflammation Pattern

The ACR Appropriateness Criteria describes a different "starry sky" pattern where conspicuous portal triads appear bright against a background of dark, edematous liver parenchyma. 1 This represents an entirely different pathophysiologic process than biliary hamartomas.

Clinical Contexts for Inflammatory "Starry Sky":

• Acute severe hepatitis (viral, toxic, or drug-induced) with diffuse hepatic hypoechogenicity and increased portal vein wall thickness 1
• Volume overload and congestive hepatopathy causing hepatic congestion 1
• Right-sided cardiac failure with hepatic edema 2

Distinguishing Features:

The inflammatory pattern differs fundamentally from biliary hamartomas:

• Acute clinical presentation with elevated aminotransferases (often >400 IU/mL in acute hepatitis) 1
• Diffuse hepatic hypoechogenicity rather than discrete small lesions 1
• Associated findings: Periportal edema on T2-weighted MRI, gallbladder wall thickening, perihepatic fluid 1
• Reversible with treatment of underlying condition, unlike the permanent structural changes of biliary hamartomas 1

Critical Diagnostic Algorithm

When encountering a reported "starry sky" pattern, immediately clarify which pattern is present:

1. If discrete 2-10 mm lesions throughout the liver: Consider biliary hamartomas

   • Confirm with MRI showing T2 hyperintense lesions without biliary communication 1
   • Reassure patient this is benign and requires no follow-up 1
   • Rule out peribiliary cysts (which have perihilar distribution and association with cirrhosis/portal hypertension) 1

2. If prominent portal triads on hypoechoic background: Consider acute inflammation

   • Assess clinical context: acute illness, volume overload, cardiac failure 1
   • Check aminotransferases, which are typically elevated in acute hepatitis 1
   • Ultrasound should be first-line imaging due to portability in acutely ill patients 1
   • Look for gallbladder wall edema and contracted gallbladder as markers of hepatic dysfunction 1

Common Pitfalls to Avoid

Do not confuse biliary hamartomas with fatty liver disease. The "bright liver" pattern of hepatic steatosis shows diffuse increased echogenicity compared to renal cortex, not discrete small lesions. 1, 3, 4 Fatty liver requires at least 20-30% hepatic fat content for ultrasound detection and appears as generalized increased echogenicity with posterior beam attenuation. 1, 5

Do not assume all "starry sky" patterns are benign. When this pattern occurs in the context of acute hepatitis with prominent portal triads on a hypoechoic background, it indicates significant hepatic inflammation requiring investigation of the underlying cause (viral hepatitis, drug toxicity, ischemic injury). 1

Recognize that ultrasound terminology is imprecise. The same descriptive term ("starry sky") is used for completely different pathologic processes—benign developmental cysts versus acute inflammation—requiring careful correlation with clinical context and additional imaging when needed. 1