Intern Emerg Med (2015) 10:721–724 DOI 10.1007/s11739-015-1264-y
EM - ORIGINAL
Prevalence of the ‘‘double-line’’ sign when performing focused assessment with sonography in trauma (FAST) examinations Amy Shah Patwa1 • Steven Cipot1 • Alvin Lomibao1 • Mathew Nelson1 • Robert Bramante1 • Veena Modayil1 • Christine Haines1 • Adam Ash1 • Christopher Raio1
Received: 1 March 2015 / Accepted: 16 May 2015 / Published online: 19 June 2015 Ó SIMI 2015
Abstract The double-line sign (DLS) is a wedge-shaped hypoechoic area in Morison’s pouch bounded on both sides by echogenic lines. It represents a false-positive finding for free intraperitoneal fluid when performing focused assessment with sonography in trauma examinations. The purpose of this study was to determine the prevalence of DLS. Secondarily, the study will further investigate the relationship between the presence of a DLS and body mass index (BMI). This was a prospective study that enrolled patients over a 7-month period. Inclusion criteria were patients C18 years of age presenting to the Emergency Department (ED) requiring a FAST examination as part of the patient’s standard medical care. Each examination was performed by one of six experienced ultrasonographers. Presence or absence of the DLS was established in real time and gender, height, weight, and BMI were recorded for each patient. The overall prevalence rate of DLS and the corresponding 95 % confidence interval were calculated, as well as the prevalence rates broken down by BMI characterized as underweight, normal weight, overweight, and obese; and age category (18–29, 30–64, and 65?). The Chi-square test and a Fisher’s exact test for BMI category were used to compare the prevalence rates of positive DLS among the different demographic groups. 100 patients were enrolled in the study; the overall prevalence was 27 %. There was no statistical significance among the different demographic groups or BMI. The DLS is a prevalent finding. We believe this sign has become more apparent due to improved imaging technology and resolution. & Adam Ash [email protected] 1
Department of Emergency Medicine, North Shore University Hospital, Manhasset, NY, USA
Keywords
Ultrasound Trauma FAST
Introduction Focused assessment with sonography in trauma (FAST) examinations is commonly performed by emergency physicians to evaluate for free intraperitoneal fluid and in the setting of trauma for hemoperitoneum. Many ultrasound findings can be misinterpreted as free fluid, resulting in false-positive FAST examinations [1, 5]. The doubleline sign (DLS) was coined by a case study, describing a thin perinephric fat pad in Morison’s pouch misinterpreted as free fluid. The DLS is a wedge-shaped hypoechoic area in Morison’s pouch that is bounded on both sides by echogenic lines [5] (Fig. 1). Free fluid has sharp edges, is often triangular in appearance and is only bound by an echogenic line on the renal border in Morison’s pouch (Fig. 2). However, such subtleties can easily be misinterpreted by the inexperienced clinician. Our study looked to determine the prevalence of the DLS on routine FAST examinations performed in the Emergency Department (ED).
Materials and methods This was a prospective study conducted at an 88,000 visit per year, Academic Level 1 Trauma Center. The study received approval from the hospital’s institutional review board, and the requirement for patient informed consent was waived. Patients were enrolled from February to September 2012. One of six emergency medicine physicians with ultrasound fellowship training independently performed FAST examinations in patients 18 years of age
123
722
Fig. 1 DLS with two hyperechoic lines bordering a small perinephric fat pad (asterisk)
Intern Emerg Med (2015) 10:721–724
reviewed at a weekly quality assurance video review to verify results, and this was considered the gold standard. Ultrasound (US) examination was carried out with curved array transducers using a z.one ultra sp ultrasound system (Zonare, Mountain View, CA). As part of a routine FAST examination, the right upper quadrant of the abdomen was examined in orthogonal planes. The DLS was considered present when a wedge-shaped hypoechoic region in Morison’s pouch was bound on both sides by hyperechoic lines. The overall prevalence rate of positive DLS and the corresponding 95 % confidence interval, were calculated, as well as the prevalence rates broken down by BMI categorized as underweight, normal weight, overweight, and obese; and age category (18–29, 30–64, and 65?). Chisquare tests and a Fisher’s exact test for BMI category were used to compare the prevalence rates of positive DLS among the different demographic groups. Statistical analysis was performed using Stata 11.1 (Stata Corp, College Station, TX), and to account for the sampling methodology, the svy command was used according to NHAMCS specifications. P = .05 was set as statistically significant.
Results
Fig. 2 Free fluid is denoted by arrow. Lone hyperechoic border of kidney marked by arrowhead
and over. The patients enrolled in the study were trauma patients who demonstrated a need for sonography to evaluate free fluid in the abdomen. At our institution it is protocol to perform a FAST exam as part of the primary survey in Level I traumas and as part of the secondary survey in Level II traumas. The vast majority of these patients were Level I and II traumas, although a few of them were minor traumas and the FAST was performed at the request of the attending physician. The presence or absence of the DLS was established in real time during the examination. Gender, height, weight, and body mass index (BMI) were also recorded for each patient. Each scan was
123
The final enrollment of the study consisted of 111 patients (age range 18–80 years; average age 41.3 years). Eleven patients were excluded from the study secondary to a failure to record patient demographics. Our results are summarized in Table 1. Among the 100 patients included in the study, the overall prevalence was found to be 27 %. The exact upper and lower 95 % confidence intervals were 36.8 and 18.6 %, respectively. All studies that were indicated as positive in real time were confirmed in quality assurance review. This study did not demonstrate any statistical significance when comparing the DLS with BMI. We also compared the prevalence of the DLS to three different age groups and did not see statistical significance amongst age and the DLS (Table 2). BMI is broken down by underweight (BMI less than 18.5),
Table 1 Prevalence of DLS and corresponding confidence intervals Overall prevalence
Real-time results
Patients with the double-line sign
27
Patients without the double-line sign Total number of patients
73 100
Prevalence
27.0 %
Exact lower 95 % confidence interval
18.6 %
Exact upper 95 % confidence interval
36.8 %
Intern Emerg Med (2015) 10:721–724 Table 2 Overall data for prevalence broken down by body mass index (BMI) and age
723
Prevalence by demographic group
n
?DLS
-DLS
Prevalence (%)
BMI Under weight
3
2
1
66.7
Normal weight
33
7
26
21.2
Over weight
32
9
23
28.1
Obese
32
9
23
28.1 26.4
Age (years) 18–29
34
9
25
30–64
50
11
39
22.0
65?
16
7
9
43.8
normal weight (BMI 18.5–24.9) and obese (BMI 30 or greater). The total number of studies with positive free fluid was 20 (20 %). Interestingly, nine of the 20 studies (45 %) had a positive DLS; the free fluid was in the pelvis for eight of the studies and in the left upper quadrant in one study. This demonstrates that the DLS is frequently present in patients who have free abdominal fluid. It should clearly never be thought to exclude pathology. It also highlights the importance of performing a thorough FAST examination, and not placing overreliance on the right upper quadrant view in these patients.
Discussion Focused assessment with sonography in trauma (FAST) is well-studied with high sensitivity and specificity for free intra-abdominal fluid, making the FAST the initial imaging modality of choice in the unstable trauma patient [3]. A recent case report that coined the term, ‘‘Double-Line Sign’’, reported an ultrasonographic finding of a wedgeshaped hypoechoic region in Morison’s pouch bound on both sides by hyperechoic lines that was misinterpreted as free intraperitoneal fluid. Particularly for those who do not regularly perform ultrasound examinations, the DLS could very well be interpreted as a positive FAST; which could alter patient management and diagnostic decision making. The two echogenic lines represent fascial planes encasing the hypoechoic fat pad, and this can have sharp borders, which is a finding classically associated with free fluid [5]. The hypoechoic area of the DLS is believed to be perinephric fat. This study also calculated the BMI for each patient to examine if there is a correlation between body habitus and the DLS. We hypothesized that patients with higher BMI’s would not exhibit the DLS due to larger diameter of perinephric fat. Our results did not find a statistically significant correlation between BMI and the DLS. Several case reports discussing various false-positive findings for hemoperitoneum stress that false-positive
results have the potential to influence patient care, sometimes adversely [3]. Depending on institutional trauma protocols, a false-positive FAST can lead to unnecessary tests or procedures, and may lead clinicians to incorrectly suspect intraperitoneal hemorrhage in unstable patients causing one to avoid looking for other causes of shock. There has also been controversy regarding the training and credentialing of clinicians performing the FAST and other focused ultrasound applications in the ED, and no consensus of standard guidelines for their training has been established [2]. There have been an increasing number of physicians incorporating the FAST examination into clinical practice, therefore delineation of this and other falsepositive findings is necessary [4]. Our study indicates that this false-positive is prevalent when performing the FAST examination, and perhaps further validates the need to train clinicians not only on technique and image acquisition, but also in diagnosis and interpretation. This study reiterates the need to have a systematic approach when performing FAST examinations and be able to identify and describe false-positive findings. This study looks at the prevalence of the DLS. Further studies identifying the DLS comparing experienced emergency sonographers with novices are needed. In addition, we believe as ultrasound technology improves prevalence will increase. Improved resolution allows for the visualization of division of fascial planes. An additional area of research could compare prevalence of the DLS across various ultrasound systems.
Limitations This study had to exclude 11 patients secondary to lack of data collection. In addition, we focused on the right upper quadrant to detect the DLS based on the fact that it is the most dependent region for free fluid collection. The descriptive case report first describing the DLS also focused on the right upper quadrant. Perhaps the data for prevalence would have increased if both the right and left
123
724
Intern Emerg Med (2015) 10:721–724
upper quadrants of the FAST examination were assessed since the DLS might also be detected in the spleno-renal recess. Additionally all of our FAST exams were performed by experienced, emergency ultrasound fellowshiptrained physicians. The prevalence of the DLS may differ if these critical examinations are performed by less experienced hands.
The DLS has become a common finding encountered when performing FAST exams. This is likely due to improvements in imaging technology and resolution over the past decade. Confusing the DLS with free intraperitoneal fluid can lead to varying forms of mismanagement in trauma patients. These range from unnecessary additional tests and procedures to misdiagnosis of other etiologies of shock in the critically ill, a potentially fatal error. Clinicians who perform FAST exams should be trained to identify this finding to minimize false-positive exams and ensure appropriate disposition of these patients.
123
Informed consent
None.
References
Conclusion
Conflict of interest of interest.
Statement of human and animal rights All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with human and animals performed by any of the authors.
The Authors declare that they have no conflict
1. Becker Alexander (2010) Is the FAST exam reliable in severely injured patients? Injury. Int J Care Inj 41:479–483 2. Jang Timothy (2004) Residents should not independently perform focused abdominal sonography for trauma after 10 training examinations. J Ultrasound Med 23:793–797 3. Kendall JL, Ramos JP (2003) Fluid-filled bowel mimicking hemoperitoneum a false-positive finding during sonographic evaluation for trauma. J Emerg Med 25:79–82 4. Nagdev A, Racht J (2008) The ‘‘gastric fluid’’ sign: an unrecognized false-positive finding during focused assessment for trauma examinations. Am J Emerg Med 26:630.e5–630.e7 5. Sierzenski Paul R, Sign The Double-Line (2011) A false positive finding on the focused assessment with sonography for trauma (FAST) examination. J Emerg Med 40(2):188–189
EM - ORIGINAL
Prevalence of the ‘‘double-line’’ sign when performing focused assessment with sonography in trauma (FAST) examinations Amy Shah Patwa1 • Steven Cipot1 • Alvin Lomibao1 • Mathew Nelson1 • Robert Bramante1 • Veena Modayil1 • Christine Haines1 • Adam Ash1 • Christopher Raio1
Received: 1 March 2015 / Accepted: 16 May 2015 / Published online: 19 June 2015 Ó SIMI 2015
Abstract The double-line sign (DLS) is a wedge-shaped hypoechoic area in Morison’s pouch bounded on both sides by echogenic lines. It represents a false-positive finding for free intraperitoneal fluid when performing focused assessment with sonography in trauma examinations. The purpose of this study was to determine the prevalence of DLS. Secondarily, the study will further investigate the relationship between the presence of a DLS and body mass index (BMI). This was a prospective study that enrolled patients over a 7-month period. Inclusion criteria were patients C18 years of age presenting to the Emergency Department (ED) requiring a FAST examination as part of the patient’s standard medical care. Each examination was performed by one of six experienced ultrasonographers. Presence or absence of the DLS was established in real time and gender, height, weight, and BMI were recorded for each patient. The overall prevalence rate of DLS and the corresponding 95 % confidence interval were calculated, as well as the prevalence rates broken down by BMI characterized as underweight, normal weight, overweight, and obese; and age category (18–29, 30–64, and 65?). The Chi-square test and a Fisher’s exact test for BMI category were used to compare the prevalence rates of positive DLS among the different demographic groups. 100 patients were enrolled in the study; the overall prevalence was 27 %. There was no statistical significance among the different demographic groups or BMI. The DLS is a prevalent finding. We believe this sign has become more apparent due to improved imaging technology and resolution. & Adam Ash [email protected] 1
Department of Emergency Medicine, North Shore University Hospital, Manhasset, NY, USA
Keywords
Ultrasound Trauma FAST
Introduction Focused assessment with sonography in trauma (FAST) examinations is commonly performed by emergency physicians to evaluate for free intraperitoneal fluid and in the setting of trauma for hemoperitoneum. Many ultrasound findings can be misinterpreted as free fluid, resulting in false-positive FAST examinations [1, 5]. The doubleline sign (DLS) was coined by a case study, describing a thin perinephric fat pad in Morison’s pouch misinterpreted as free fluid. The DLS is a wedge-shaped hypoechoic area in Morison’s pouch that is bounded on both sides by echogenic lines [5] (Fig. 1). Free fluid has sharp edges, is often triangular in appearance and is only bound by an echogenic line on the renal border in Morison’s pouch (Fig. 2). However, such subtleties can easily be misinterpreted by the inexperienced clinician. Our study looked to determine the prevalence of the DLS on routine FAST examinations performed in the Emergency Department (ED).
Materials and methods This was a prospective study conducted at an 88,000 visit per year, Academic Level 1 Trauma Center. The study received approval from the hospital’s institutional review board, and the requirement for patient informed consent was waived. Patients were enrolled from February to September 2012. One of six emergency medicine physicians with ultrasound fellowship training independently performed FAST examinations in patients 18 years of age
123
722
Fig. 1 DLS with two hyperechoic lines bordering a small perinephric fat pad (asterisk)
Intern Emerg Med (2015) 10:721–724
reviewed at a weekly quality assurance video review to verify results, and this was considered the gold standard. Ultrasound (US) examination was carried out with curved array transducers using a z.one ultra sp ultrasound system (Zonare, Mountain View, CA). As part of a routine FAST examination, the right upper quadrant of the abdomen was examined in orthogonal planes. The DLS was considered present when a wedge-shaped hypoechoic region in Morison’s pouch was bound on both sides by hyperechoic lines. The overall prevalence rate of positive DLS and the corresponding 95 % confidence interval, were calculated, as well as the prevalence rates broken down by BMI categorized as underweight, normal weight, overweight, and obese; and age category (18–29, 30–64, and 65?). Chisquare tests and a Fisher’s exact test for BMI category were used to compare the prevalence rates of positive DLS among the different demographic groups. Statistical analysis was performed using Stata 11.1 (Stata Corp, College Station, TX), and to account for the sampling methodology, the svy command was used according to NHAMCS specifications. P = .05 was set as statistically significant.
Results
Fig. 2 Free fluid is denoted by arrow. Lone hyperechoic border of kidney marked by arrowhead
and over. The patients enrolled in the study were trauma patients who demonstrated a need for sonography to evaluate free fluid in the abdomen. At our institution it is protocol to perform a FAST exam as part of the primary survey in Level I traumas and as part of the secondary survey in Level II traumas. The vast majority of these patients were Level I and II traumas, although a few of them were minor traumas and the FAST was performed at the request of the attending physician. The presence or absence of the DLS was established in real time during the examination. Gender, height, weight, and body mass index (BMI) were also recorded for each patient. Each scan was
123
The final enrollment of the study consisted of 111 patients (age range 18–80 years; average age 41.3 years). Eleven patients were excluded from the study secondary to a failure to record patient demographics. Our results are summarized in Table 1. Among the 100 patients included in the study, the overall prevalence was found to be 27 %. The exact upper and lower 95 % confidence intervals were 36.8 and 18.6 %, respectively. All studies that were indicated as positive in real time were confirmed in quality assurance review. This study did not demonstrate any statistical significance when comparing the DLS with BMI. We also compared the prevalence of the DLS to three different age groups and did not see statistical significance amongst age and the DLS (Table 2). BMI is broken down by underweight (BMI less than 18.5),
Table 1 Prevalence of DLS and corresponding confidence intervals Overall prevalence
Real-time results
Patients with the double-line sign
27
Patients without the double-line sign Total number of patients
73 100
Prevalence
27.0 %
Exact lower 95 % confidence interval
18.6 %
Exact upper 95 % confidence interval
36.8 %
Intern Emerg Med (2015) 10:721–724 Table 2 Overall data for prevalence broken down by body mass index (BMI) and age
723
Prevalence by demographic group
n
?DLS
-DLS
Prevalence (%)
BMI Under weight
3
2
1
66.7
Normal weight
33
7
26
21.2
Over weight
32
9
23
28.1
Obese
32
9
23
28.1 26.4
Age (years) 18–29
34
9
25
30–64
50
11
39
22.0
65?
16
7
9
43.8
normal weight (BMI 18.5–24.9) and obese (BMI 30 or greater). The total number of studies with positive free fluid was 20 (20 %). Interestingly, nine of the 20 studies (45 %) had a positive DLS; the free fluid was in the pelvis for eight of the studies and in the left upper quadrant in one study. This demonstrates that the DLS is frequently present in patients who have free abdominal fluid. It should clearly never be thought to exclude pathology. It also highlights the importance of performing a thorough FAST examination, and not placing overreliance on the right upper quadrant view in these patients.
Discussion Focused assessment with sonography in trauma (FAST) is well-studied with high sensitivity and specificity for free intra-abdominal fluid, making the FAST the initial imaging modality of choice in the unstable trauma patient [3]. A recent case report that coined the term, ‘‘Double-Line Sign’’, reported an ultrasonographic finding of a wedgeshaped hypoechoic region in Morison’s pouch bound on both sides by hyperechoic lines that was misinterpreted as free intraperitoneal fluid. Particularly for those who do not regularly perform ultrasound examinations, the DLS could very well be interpreted as a positive FAST; which could alter patient management and diagnostic decision making. The two echogenic lines represent fascial planes encasing the hypoechoic fat pad, and this can have sharp borders, which is a finding classically associated with free fluid [5]. The hypoechoic area of the DLS is believed to be perinephric fat. This study also calculated the BMI for each patient to examine if there is a correlation between body habitus and the DLS. We hypothesized that patients with higher BMI’s would not exhibit the DLS due to larger diameter of perinephric fat. Our results did not find a statistically significant correlation between BMI and the DLS. Several case reports discussing various false-positive findings for hemoperitoneum stress that false-positive
results have the potential to influence patient care, sometimes adversely [3]. Depending on institutional trauma protocols, a false-positive FAST can lead to unnecessary tests or procedures, and may lead clinicians to incorrectly suspect intraperitoneal hemorrhage in unstable patients causing one to avoid looking for other causes of shock. There has also been controversy regarding the training and credentialing of clinicians performing the FAST and other focused ultrasound applications in the ED, and no consensus of standard guidelines for their training has been established [2]. There have been an increasing number of physicians incorporating the FAST examination into clinical practice, therefore delineation of this and other falsepositive findings is necessary [4]. Our study indicates that this false-positive is prevalent when performing the FAST examination, and perhaps further validates the need to train clinicians not only on technique and image acquisition, but also in diagnosis and interpretation. This study reiterates the need to have a systematic approach when performing FAST examinations and be able to identify and describe false-positive findings. This study looks at the prevalence of the DLS. Further studies identifying the DLS comparing experienced emergency sonographers with novices are needed. In addition, we believe as ultrasound technology improves prevalence will increase. Improved resolution allows for the visualization of division of fascial planes. An additional area of research could compare prevalence of the DLS across various ultrasound systems.
Limitations This study had to exclude 11 patients secondary to lack of data collection. In addition, we focused on the right upper quadrant to detect the DLS based on the fact that it is the most dependent region for free fluid collection. The descriptive case report first describing the DLS also focused on the right upper quadrant. Perhaps the data for prevalence would have increased if both the right and left
123
724
Intern Emerg Med (2015) 10:721–724
upper quadrants of the FAST examination were assessed since the DLS might also be detected in the spleno-renal recess. Additionally all of our FAST exams were performed by experienced, emergency ultrasound fellowshiptrained physicians. The prevalence of the DLS may differ if these critical examinations are performed by less experienced hands.
The DLS has become a common finding encountered when performing FAST exams. This is likely due to improvements in imaging technology and resolution over the past decade. Confusing the DLS with free intraperitoneal fluid can lead to varying forms of mismanagement in trauma patients. These range from unnecessary additional tests and procedures to misdiagnosis of other etiologies of shock in the critically ill, a potentially fatal error. Clinicians who perform FAST exams should be trained to identify this finding to minimize false-positive exams and ensure appropriate disposition of these patients.
123
Informed consent
None.
References
Conclusion
Conflict of interest of interest.
Statement of human and animal rights All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with human and animals performed by any of the authors.
The Authors declare that they have no conflict
1. Becker Alexander (2010) Is the FAST exam reliable in severely injured patients? Injury. Int J Care Inj 41:479–483 2. Jang Timothy (2004) Residents should not independently perform focused abdominal sonography for trauma after 10 training examinations. J Ultrasound Med 23:793–797 3. Kendall JL, Ramos JP (2003) Fluid-filled bowel mimicking hemoperitoneum a false-positive finding during sonographic evaluation for trauma. J Emerg Med 25:79–82 4. Nagdev A, Racht J (2008) The ‘‘gastric fluid’’ sign: an unrecognized false-positive finding during focused assessment for trauma examinations. Am J Emerg Med 26:630.e5–630.e7 5. Sierzenski Paul R, Sign The Double-Line (2011) A false positive finding on the focused assessment with sonography for trauma (FAST) examination. J Emerg Med 40(2):188–189
