In an adult patient suspected of fatty liver, what colour pattern on contrast‑enhanced ultrasound indicates a zone free of steatosis?

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CEUS Pattern in Zones Free of Steatosis

Zones free of steatosis (focal fatty sparing) on contrast-enhanced ultrasound demonstrate isoenhancement with adjacent liver parenchyma in all phases, appearing identical to normal liver tissue despite the surrounding fatty infiltration.

Enhancement Characteristics of Focal Fatty Sparing

Arterial Phase Pattern

  • Focal fatty sparing shows significantly lower and slower enhancement compared to adjacent steatotic parenchyma during the arterial phase, with reduced peak enhancement, wash-in area under the curve, wash-in rate, and wash-in perfusion index 1
  • Approximately 73% of focal fatty sparing lesions appear subjectively isoenhancing in the arterial phase, while 27% appear hypoenhancing 1
  • The quantitative parameters reveal that focal fatty sparing has significantly lower wash-in rates compared to focal fatty infiltration 1

Portal and Delayed Phases

  • All focal fatty sparing lesions demonstrate isoenhancement with surrounding liver parenchyma in the venous and delayed phases 1
  • The three stages of focal fat loss show synchronized and simultaneous enhancement with surrounding fatty liver tissues throughout all contrast phases 2

Key Distinguishing Features

Differentiation from Other Lesions

  • Unlike malignant lesions, focal fatty sparing shows no wash-out in the late phase, maintaining isoenhancement throughout 1, 2
  • Focal fatty sparing produces similar time-intensity curve patterns to normal liver parenchyma, with no significant differences in contrast uptake characteristics 3
  • The enhancement pattern differs from liver cysts (which show no enhancement in any phase) and liver abscesses (which show ring-shaped enhancement in arterial phase) 2

Quantitative Assessment Advantages

  • CEUS provides 90.48% diagnostic accuracy for intrahepatic space-occupying lesions in fatty liver backgrounds, significantly superior to conventional ultrasound's 61.90% accuracy 2
  • The area under the diagnostic curve for CEUS (0.809) is substantially higher than conventional ultrasound (0.668) in this clinical context 2

Clinical Implications

Diagnostic Approach

  • The isoenhancement pattern throughout all phases is the hallmark finding that distinguishes focal fatty sparing from true focal lesions requiring further investigation 1, 2
  • Quantitative analysis reveals that focal fatty sparing has slower enhancement kinetics than surrounding steatotic tissue, though this may not be apparent on subjective visual assessment 1

Important Caveats

  • While subjective assessment suggests isoenhancement in most cases, quantitative analysis reveals subtle differences in enhancement parameters that may not be visually apparent 1
  • The diagnostic accuracy of CEUS is significantly enhanced when combined with analysis of enhancement patterns across all three vascular phases rather than relying on a single phase 2

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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