Qualitative assessment of hepatic steatosis on modern grayscale ultrasound: more accurate than previously thought?

OBJECTIVE

To assess the diagnostic performance of standardized qualitative assessment of hepatic steatosis on grayscale ultrasound.

METHODS

This retrospective, single-center, multi-case, multi-reader study included 200 patients with ultrasound examinations of the liver. Three readers assessed hepatic steatosis based on a standardized system of 3 ultrasound features: presence of increased fine echoes, visualization of right hemidiaphragm, and visualization of portal triads, assigning a four-grade category (normal, mild, moderate, or severe). Magnetic resonance imaging proton density fat fraction (MRI-PDFF) was used as reference standard. Binary discrimination (normal vs. steatosis) was summarized with binary area under the curve (AUC), sensitivity, and specificity. Discrimination across four categories was performed with pairwise comparisons. Reader differences were tested with the Obuchowski-Rockette-Hillis model. Inter-reader agreement was calculated with Gwet's agreement coefficient (AC).

RESULTS

Of the 200 patients, 27% (54/200) had normal liver (MRI-PDFF < 5%), 35% (70/200) had mild steatosis (MRI-PDFF ≥ 5-17.4%), 15% (29/200) had moderate steatosis (MRI-PDFF > 17.4-22.1%), and 24% (47/200) had severe steatosis (MRI-PDFF > 22.1%). Median time interval between ultrasound and MRI exams was 4 days (IQR 1-28). Sensitivity, specific, and binary AUC for readers 1/2/3 were 90%/82%/94%, 65%/82%/54%, and 0.87/0.85/0.88 with no statistically significant difference between readers (p = 0.46). Four-class category analysis showed excellent performance of ultrasound to distinguish extreme categories (AUC > 0.95 for normal vs. severe). Inter-reader agreement was substantial (Gwet's AC 0.63) for steatosis category assignment and moderate to substantial (Gwet's AC 0.55-0.71) for ultrasound features.

CONCLUSION

Contrary to popular belief, qualitative ultrasound assessment of hepatic steatosis is accurate in detecting and grading steatosis when evaluation criteria are standardized.