The Lipliner Artifact is a Frequent Mimic of Free Fluid in FAST Exams

The Focused Assessment of Sonography in Trauma (FAST) evaluates for free fluid (FF) as an indicator for operative intervention. The lipliner (LL) is a hypoechoic artifact tracking along the edge of the liver or spleen, mimicking FF during the FAST. This results from despeckling algorithms used to demarcate borders. We evaluated the prevalence of the LL in the right (RUQ) and left upper quadrants (LUQ). Secondary outcomes evaluated the impact of patient demographics and machine specifics on the prevalence of the LL.

This was a retrospective, observational study of FAST and eFAST exams from December 2023 to May 2024 and an interval evaluation from December 2024 to February 2025. Eligible exams had patient identifiers, adequate images, and an available computed tomography (CT) of the abdomen and pelvis or operative report (OR) as the criterion standard for FF. Presence or absence of the LL was determined by agreement. Investigators interpreted the RUQ and LUQ for FF and the LL and the pelvis for FF. An interrater repeated the analysis. Disagreements were adjudicated by a blinded third reviewer. Interrater agreement was assessed by Cohen's Kappa. Descriptive analysis of clinical and demographic variables used means, standard deviation, frequencies and percentages. The analysis employed R Software. Chi-square and Fisher’s exact tests compared prevalence of the LL across demographic and machine-specific groups.

1,034 FAST and eFAST studies were included. Of the 839 (84.4%) studies without FF by CT or OR, the LL was observed in 30.0% (252) of RUQs and in 13.8% (116) of LUQs. 72.2% of RUQ interpretations and 74.5% of LUQ interpretations showed agreement between the initial rater and interrater; the agreement was moderate (κ=0.41) in the RUQ and fair (κ=0.29) in the LUQ. Of the 195 (15.6%) studies with FF by CT or OR, 21.0% were falsely interpreted as a LL in the RUQ and 8.7% as a LL in the LUQ.

The LL impacts the diagnostic performance of the FAST exam. Agreement results highlight how confusing the artifact can be. Next steps should focus on preset adjustments and despeckling methods in order to reduce or eliminate the artifact.