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September 23, 2024
Written by Megan Hilbert
Post-processing techniques completed by ultrasound machines to improve spatial resolution have become so advanced that it can now fool us into thinking a FAST exam is positive.
The physics is trying to fool me?!
False positives on the FAST exam can lead to resource-intensive work-ups that may not be medically necessary. This can increase ED lengths of stay, patient exposure to ionizing radiation, and healthcare costs. This makes it extremely important to have high specificity when it comes to the completion of our FAST exam. This paper highlights an entity known as “lipliner” sign where there is a hypoechoic line visualized by the caudal tip of the liver and spleen that is commonly misinterpreted as a positive FAST exam. It is thought to be due to image adaptive filtering (post-processing, non-anatomic artifact) and has been demonstrated across multiple ultrasound machines/manufacturers. The authors suggest that if this artifact is identified, providers should interpret the study as “indeterminate” and make sure not to anchor on a diagnosis of hemoperitoneum.
Aside: Lipliner sign is not double line sign (DLS)! DLS is when a wedge-shaped hypoechoic region is visualized in Morrison’s pouch. This is representative of perinephric fat and appears hypoechoic because it is bounded by two echogenic lines of fascial planes surrounding the adjacent organs. While not the same, it can also be a hemoperitoneum mimic. See comparison below (Lipliner in red, DLS in yellow).
How will this change my practice?
Like so many other things in medicine, you don’t know what you don’t know. Making providers aware of this hemoperitoneum mimic should hopefully help guide judicious work-ups for patients presenting to the ED with trauma.
Source
The Lipliner Sign: Potential Cause of a False Positive FAST Examination. Journal of Emergency Medicine, June 28, 2024; https://doi.org/10.1016/j.jemermed.2024.06.013
