The Lipliner Sign: Potential Cause of a False Positive Focused Assessment with Sonography in Trauma (FAST) Examination.

Background: The focused assessment with sonography in trauma (FAST) examination plays an essential role in diagnosing hemoperitoneum in trauma patients to guide prompt operative management. The FAST examination is highly specific for hemoperitoneum in trauma patients, and has been adopted in nontrauma patients to identify intraperitoneal fluid as a cause of abdominal pain or distension. However, causes of false positive FAST examinations have been described and require prompt recognition to avoid diagnostic uncertainty and inappropriate procedures. Most causes of false positive FAST examinations are due to anatomic mimics such as perinephric fat or seminal vesicles, however, modern ultrasound machines use a variety of postprocessing image enhancement techniques that can also lead to novel false positive artifacts.

Case report: We report cases where experienced clinicians incorrectly interpreted ultrasound findings caused by a novel mimic of hemoperitoneum: the "lipliner sign." It appears most prominently at the edges of solid organs (such as the liver and the spleen), which is the same location most likely to show free fluid in FAST examination in trauma patients. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Clinicians who take care of trauma patients must be familiar with causes of false positive FAST examinations that could lead to a misdiagnosis of hemoperitoneum.