The double-line sign: a false positive finding on the Focused Assessment with Sonography for Trauma (FAST) examination.
BACKGROUND
Emergency physicians commonly perform Focused Assessment with Sonography for Trauma (FAST) examinations to evaluate for free intraperitoneal fluid. Many ultrasound findings can be misinterpreted as free fluid, resulting in false-positive FAST examinations.


OBJECTIVE
To describe a previously unreported ultrasound finding that can be misinterpreted as free intraperitoneal fluid.


METHODS
A 32-year-old man was stabbed in the left upper abdomen. A FAST examination was performed and a right perinephric fat pad was interpreted as showing free fluid in Morison's pouch. After transfer to a trauma center, a repeat FAST examination revealed no signs of intraperitoneal free fluid. Wound exploration showed no signs of penetration into the peritoneal cavity.


CONCLUSIONS
When performing a FAST examination, a wedge-shaped hypoechoic area in Morison's pouch that is bounded on both sides by echogenic lines (the "FAST Double-Line Sign") is likely to represent perinephric fat and may result in a false-positive FAST examination.
Sierzenski
Paul R
PR
Section of Emergency Ultrasound, Department of Emergency Medicine, Christiana Care Health System, Newark, Delaware, USA.
Schofer
Joel M
JM
Bauman
Michael J
MJ
Nomura
Jason T
JT
D000007:Abdominal Injuries / Q000000981:diagnostic imaging*; D000328:Adult; D001202:Ascitic Fluid / Q000000981:diagnostic imaging*; D005189:False Positive Reactions; D006801:Humans; D008297:Male; D010529:Peritoneal Cavity / Q000000981:diagnostic imaging; D014463:Ultrasonography; D014951:Wounds, Stab / Q000000981:diagnostic imaging*