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The Double-Line Sign: A False Positive Finding on the Focused Assessment with Sonography for Trauma (FAST) Examination
The Journal of Emergency Medicine, Vol. 40, No. 2, pp. 188 –189, 2011 Published by Elsevier Inc. Printed in the USA 0736-4679/$–see front matter
doi:10.1016/j.jemermed.2009.07.029
Ultrasound in Emergency Medicine
THE DOUBLE-LINE SIGN: A FALSE POSITIVE FINDING ON THE FOCUSED ASSESSMENT WITH SONOGRAPHY FOR TRAUMA (FAST) EXAMINATION Paul R. Sierzenski,
MD, RDMS,
Joel M. Schofer, MD, LCDR MC USN, Michael J. Bauman, Jason T. Nomura, MD, RDMS
MD,
and
Section of Emergency Ultrasound, Department of Emergency Medicine, Christiana Care Health System, Newark, Delaware Corresponding Address: Joel M. Schofer, MD, LCDR MC USN, Department of Emergency Medicine, Christiana Care Health System, 602 Geddes St., Wilmington, DE 19805
e Abstract—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. Objectives: To describe a previously unreported ultrasound finding that can be misinterpreted as free intraperitoneal fluid. Case Report: 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 falsepositive FAST examination. Published by Elsevier Inc.
INTRODUCTION Emergency physicians commonly perform focused assessment with sonography for trauma (FAST) examinations to evaluate for free intraperitoneal fluid consistent with hemoperitoneum or ascites. Many ultrasound findings have been described that mimic free intraperitoneal fluid and can be misinterpreted, resulting in a false-positive FAST examination (1– 4). A false-positive FAST examination may lead to unnecessary additional radiologic interventions or procedures, including computed tomography, diagnostic peritoneal lavage, or laparotomy. This report describes a previously unreported ultrasound finding that simulates free intraperitoneal fluid and can lead to a false-positive FAST examination.
CASE REPORT A 32-year-old man presented to the Emergency Department of a community teaching hospital after sustaining a stab wound to the left upper quadrant of the abdomen. His initial vital signs showed a blood pressure of 147/45 mm Hg, heart rate of 123 beats/min, and respiratory rate of 24 breaths/min. The stab wound demonstrated profuse arterial bleeding and his examination was otherwise unremarkable. A FAST examination was performed and interpreted as showing free intraperitoneal fluid in Mori-
e Keywords—ultrasound; trauma; hemoperitoneum; focused assessment with sonography for trauma; falsepositive
The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States government.
RECEIVED: 15 April 2009; FINAL ACCEPTED: 23 July 2009
SUBMISSION RECEIVED:
23 June 2009; 188
Double-Line Sign
189
Figure 1. Ultrasound image of the patient’s Morison’s pouch. Figure 3. Ultrasound image of another patient’s Morison’s pouch demonstrating free intraperitoneal fluid.
son’s pouch (Figures 1, 2). The patient was intubated and transferred to a local Level I trauma center. At the trauma center, a repeat FAST examination was performed and was interpreted as negative for intraperitoneal free fluid. Local wound exploration revealed a severed superior epigastric artery, with no signs of penetration beyond the posterior rectus sheath or into the peritoneal cavity.
DISCUSSION A Perinephric Fat Pad and “FAST Double-Line Sign” Representing a False-positive FAST Examination Morison’s pouch is the most common location of free intraperitoneal fluid in the trauma patient (1). A number of structures present near Morison’s pouch may mimic free fluid and lead to a false-positive FAST examination. In this case, a perinephric fat pad was mistaken for free fluid. Other false positives include a portion of the small intestine, hepatic flexure of the colon, gallbladder, or a renal cyst (1– 4). All of the causes of false-positive FAST examinations listed above demonstrate a hypoechoic area that is bordered on both the renal and hepatic sides by echogenic
lines, which we term the “FAST Double-Line Sign.” In the case of a perinephric fat pad, a normal anatomic structure, the echogenic lines are caused by fascial planes encasing the hypoechoic fat pad, which can have a sharp corner, a finding classically associated with free fluid. Small intestine, colon, gallbladder, and renal cysts all have echogenic lines, representing the walls of the structure, surrounding hypoechoic fluid that typically has rounded corners. In addition, perinephric fat pads will typically contain low-level echoes within the hypoechoic region, similar to a pericardial fat pad, and move with the kidney as it changes position during respiration. CONCLUSIONS When performing a FAST examination, a wedge-shaped hypoechoic area in Morison’s pouch that is bounded on both the hepatic and renal sides by echogenic lines, the “FAST Double-Line Sign,” is likely to represent perinephric fat and may result in a false-positive FAST examination. Contrast-free intraperitoneal fluid in Morison’s pouch is often bounded by only one echogenic line as it abuts the kidney, but an echogenic line is usually absent on the hepatic side of the free fluid (Figure 3). REFERENCES
Figure 2. Ultrasound image of the patient’s Morison’s pouch.
1. McKenney KL, Nunez DB, McKenney MG, et al. Ultrasound for blunt abdominal trauma: is it free fluid? Emerg Radiol 1998;5: 203–9. 2. Kendall JL, Ramos JP. Fluid-filled bowel mimicking hemoperitoneum: a false-positive finding during sonographic evaluation for trauma. J Emerg Med 2003;25:79 – 82. 3. McElveen TS, Collin GR. The role of ultrasonography in blunt abdominal trauma: a prospective study. Am Surg 1997;63:184 – 8. 4. Nagdev A, Racht J. The “gastric fluid” sign: an unrecognized false-positive finding during focused assessment for trauma examinations. Am J Emerg Med 2008;26:630.e5–7.
doi:10.1016/j.jemermed.2009.07.029
Ultrasound in Emergency Medicine
THE DOUBLE-LINE SIGN: A FALSE POSITIVE FINDING ON THE FOCUSED ASSESSMENT WITH SONOGRAPHY FOR TRAUMA (FAST) EXAMINATION Paul R. Sierzenski,
MD, RDMS,
Joel M. Schofer, MD, LCDR MC USN, Michael J. Bauman, Jason T. Nomura, MD, RDMS
MD,
and
Section of Emergency Ultrasound, Department of Emergency Medicine, Christiana Care Health System, Newark, Delaware Corresponding Address: Joel M. Schofer, MD, LCDR MC USN, Department of Emergency Medicine, Christiana Care Health System, 602 Geddes St., Wilmington, DE 19805
e Abstract—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. Objectives: To describe a previously unreported ultrasound finding that can be misinterpreted as free intraperitoneal fluid. Case Report: 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 falsepositive FAST examination. Published by Elsevier Inc.
INTRODUCTION Emergency physicians commonly perform focused assessment with sonography for trauma (FAST) examinations to evaluate for free intraperitoneal fluid consistent with hemoperitoneum or ascites. Many ultrasound findings have been described that mimic free intraperitoneal fluid and can be misinterpreted, resulting in a false-positive FAST examination (1– 4). A false-positive FAST examination may lead to unnecessary additional radiologic interventions or procedures, including computed tomography, diagnostic peritoneal lavage, or laparotomy. This report describes a previously unreported ultrasound finding that simulates free intraperitoneal fluid and can lead to a false-positive FAST examination.
CASE REPORT A 32-year-old man presented to the Emergency Department of a community teaching hospital after sustaining a stab wound to the left upper quadrant of the abdomen. His initial vital signs showed a blood pressure of 147/45 mm Hg, heart rate of 123 beats/min, and respiratory rate of 24 breaths/min. The stab wound demonstrated profuse arterial bleeding and his examination was otherwise unremarkable. A FAST examination was performed and interpreted as showing free intraperitoneal fluid in Mori-
e Keywords—ultrasound; trauma; hemoperitoneum; focused assessment with sonography for trauma; falsepositive
The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States government.
RECEIVED: 15 April 2009; FINAL ACCEPTED: 23 July 2009
SUBMISSION RECEIVED:
23 June 2009; 188
Double-Line Sign
189
Figure 1. Ultrasound image of the patient’s Morison’s pouch. Figure 3. Ultrasound image of another patient’s Morison’s pouch demonstrating free intraperitoneal fluid.
son’s pouch (Figures 1, 2). The patient was intubated and transferred to a local Level I trauma center. At the trauma center, a repeat FAST examination was performed and was interpreted as negative for intraperitoneal free fluid. Local wound exploration revealed a severed superior epigastric artery, with no signs of penetration beyond the posterior rectus sheath or into the peritoneal cavity.
DISCUSSION A Perinephric Fat Pad and “FAST Double-Line Sign” Representing a False-positive FAST Examination Morison’s pouch is the most common location of free intraperitoneal fluid in the trauma patient (1). A number of structures present near Morison’s pouch may mimic free fluid and lead to a false-positive FAST examination. In this case, a perinephric fat pad was mistaken for free fluid. Other false positives include a portion of the small intestine, hepatic flexure of the colon, gallbladder, or a renal cyst (1– 4). All of the causes of false-positive FAST examinations listed above demonstrate a hypoechoic area that is bordered on both the renal and hepatic sides by echogenic
lines, which we term the “FAST Double-Line Sign.” In the case of a perinephric fat pad, a normal anatomic structure, the echogenic lines are caused by fascial planes encasing the hypoechoic fat pad, which can have a sharp corner, a finding classically associated with free fluid. Small intestine, colon, gallbladder, and renal cysts all have echogenic lines, representing the walls of the structure, surrounding hypoechoic fluid that typically has rounded corners. In addition, perinephric fat pads will typically contain low-level echoes within the hypoechoic region, similar to a pericardial fat pad, and move with the kidney as it changes position during respiration. CONCLUSIONS When performing a FAST examination, a wedge-shaped hypoechoic area in Morison’s pouch that is bounded on both the hepatic and renal sides by echogenic lines, the “FAST Double-Line Sign,” is likely to represent perinephric fat and may result in a false-positive FAST examination. Contrast-free intraperitoneal fluid in Morison’s pouch is often bounded by only one echogenic line as it abuts the kidney, but an echogenic line is usually absent on the hepatic side of the free fluid (Figure 3). REFERENCES
Figure 2. Ultrasound image of the patient’s Morison’s pouch.
1. McKenney KL, Nunez DB, McKenney MG, et al. Ultrasound for blunt abdominal trauma: is it free fluid? Emerg Radiol 1998;5: 203–9. 2. Kendall JL, Ramos JP. Fluid-filled bowel mimicking hemoperitoneum: a false-positive finding during sonographic evaluation for trauma. J Emerg Med 2003;25:79 – 82. 3. McElveen TS, Collin GR. The role of ultrasonography in blunt abdominal trauma: a prospective study. Am Surg 1997;63:184 – 8. 4. Nagdev A, Racht J. The “gastric fluid” sign: an unrecognized false-positive finding during focused assessment for trauma examinations. Am J Emerg Med 2008;26:630.e5–7.