Is ultrasound (USG) a reliable diagnostic tool for Metabolic Associated Steatohepatitis (MASLD)?

Feasibility of Ultrasound in MASLD Diagnosis

Ultrasound is appropriate as a first-line screening tool for detecting hepatic steatosis in MASLD, but it has significant limitations and cannot reliably diagnose steatohepatitis (MASH), grade steatosis severity, or assess fibrosis. 1

Role as a Screening Modality

Ultrasound serves as the primary screening examination for MASLD in high-risk populations, including patients with diabetes, metabolic syndrome, obesity, and elevated liver enzymes. 1, 2 The 2021 Korean Association for the Study of the Liver guidelines explicitly recommend abdominal ultrasonography as the primary screening modality. 1

Strengths for Initial Detection:

• Wide availability and non-invasive nature make it practical for population-level screening 1
• Robust diagnostic performance for moderate-to-severe steatosis (>30% hepatocyte involvement) 1
• Ability to evaluate the entire hepatobiliary system simultaneously, potentially identifying other pathology 1

Critical Limitations

Cannot Diagnose MASH:

Conventional ultrasound cannot distinguish simple steatosis from steatohepatitis because it cannot assess microscopic features like hepatocyte ballooning or lobular inflammation. 1 The 2024 EASL-EASD-EASO guidelines explicitly state that none of the non-invasive imaging methods, including ultrasound, can assess these relevant microscopic features of MASLD. 1

Poor Performance for Grading Steatosis:

• Sensitivity drops dramatically when steatosis is <30% 1
• Subjective interpretation leads to inconsistent grading 1
• In pediatric studies (applicable principles to adults), positive predictive value was only 47-62% for fatty liver diagnosis 1
• Children classified as "mild steatosis" by ultrasound had moderate steatosis on histology in ~50% of cases 1

Cannot Assess Fibrosis:

Standard B-mode ultrasound has no capability to stage fibrosis, which is the most critical prognostic factor in MASLD. 1, 3 This represents a major clinical limitation since fibrosis stage determines risk stratification and management intensity.

Technical Limitations:

• Reduced sensitivity in obese patients due to poor acoustic windows 1
• Cannot detect early-stage hepatocellular carcinoma reliably, particularly in MASLD cirrhosis with obesity 1

When Ultrasound Findings Are Insufficient

When ultrasound suggests steatosis, additional testing is mandatory for proper risk stratification:

For Fibrosis Assessment:

• Calculate FIB-4 score as first-tier assessment (using AST, ALT, age, platelets) 2, 4
• If FIB-4 is indeterminate (1.3-2.67) or elevated (>2.67), proceed to vibration-controlled transient elastography (VCTE) or other elastography methods 1, 2
• Enhanced Liver Fibrosis (ELF) test can serve as alternative to elastography for detecting advanced fibrosis 1, 2

For Steatosis Quantification:

• MRI with proton density fat fraction (MRI-PDFF) is superior for accurate steatosis quantification 1
• Controlled attenuation parameter (CAP) via transient elastography provides quantitative steatosis assessment 1

For MASH Diagnosis:

• Liver biopsy remains the only definitive method to diagnose steatohepatitis and assess ballooning/inflammation 1
• Emerging multiparametric ultrasound techniques (viscosity measurements, shear-wave elastography) show promise but are not yet standard practice 5

Practical Clinical Algorithm

1. Use ultrasound for initial screening in high-risk patients (diabetes, metabolic syndrome, elevated transaminases) 1, 2

2. If ultrasound shows steatosis:

   • Calculate FIB-4 score immediately 2, 4
   • If FIB-4 <1.3: Low risk, repeat assessment in 6-12 months 2
   • If FIB-4 1.3-2.67: Proceed to VCTE or ELF testing 1, 2
   • If FIB-4 >2.67: High risk, refer to hepatology and perform VCTE 1, 2

3. Do not rely on ultrasound alone for treatment decisions or severity grading 1

4. For HCC surveillance in MASLD cirrhosis, combine ultrasound with alpha-fetoprotein measurement due to ultrasound's low sensitivity, particularly in obese patients 1

Common Pitfalls to Avoid

• Do not use ultrasound to exclude significant fibrosis – it cannot assess this critical parameter 1, 3
• Do not assume normal ultrasound excludes MASLD – sensitivity is poor for mild steatosis (<30%) 1
• Do not use ultrasound grading (mild/moderate/severe) for clinical decisions – correlation with histology is poor 1
• Do not delay fibrosis assessment based on ultrasound appearance alone – always calculate FIB-4 2