Many emergency departments use ultrasound on a daily basis to assess patients. The FAST protocol and its variant e-FAST allow the rapid assessment of severe trauma patients. However, there is a lack of standardization in the different training programs and especially in the teaching of the FAST protocol [10].
Located in the retroperitoneum, the seminal vesicles contain fluid that can have a hypoechoic appearance in the ultrasound images of the male pelvis (Fig. 1, Additional file 1: video S1). Although poorly studied, this hypoechoic structure may be misinterpreted as free fluid. In male patients, free fluid is located in the Douglas pouch, never next to or directly above the prostate, but rather more cranially at the level of the bladder. Figure 2 shows a transverse ultrasound view of the male pelvis above the seminal vesicles, whereas Fig. 3 and Additional file 2: video S2 show a pathological ultrasound view of the male pelvis with free fluid. Our study suggests that the seminal vesicles are a potential POCUS pitfall when assessing the presence of free fluid in the male pelvis. Among the ultrasound images included in the survey, only the seminal vesicles could be the source of misinterpretation for free fluid. The completion of the survey by three external radiologists to confirm the quality of the chosen ultrasound transverse pelvic views gives methodological strength to this study.
Although participants were given information about the view and location of the ultrasound images as well as the gender of the volunteers, seminal vesicles were not specially mentioned in order to avoid influencing responses. All included participants described themselves as familiar with the FAST protocol, and only one participant had not received clinical ultrasound training. Participants’ knowledge may thus be considered representative of ultrasound training courses, as they had a heterogeneous background in ultrasound imaging. This study also significantly demonstrates that dynamic examinations of the pelvic region reduce the number of misinterpretations compared to static images. This enlightens the importance of using dynamic, rather than static, assessment of ultrasound images during a FAST examination. This dynamic assessment should cover the region. As the participants were not given the opportunity to repeat the survey or return to a previous question, their initial responses could not be changed after the subsequent viewing of static or dynamic images. Since this study only aims to highlight the false-positive rate, no pathological image was included in the survey.
The absence of a pathological image may nevertheless have influenced the certainty index of participants’ responses, as they may have interpreted images according to the following yes–no question: is free fluid visible in this transverse ultrasound image of the male pelvis? However, the survey used carefully chosen sentences to avoid influencing participants about the possible absence or presence of free fluid.
The exclusive use of a transverse section view without a longitudinal view may be cited as a limitation of this study. Indeed, the e-FAST protocol strictly recommends the use of a transverse view along with a longitudinal view to assess the presence of free fluid in the pelvis [13]. Complementary studies should therefore clarify whether the additional use of a longitudinal ultrasound view decreases the number of misinterpretations.
Another limitation of this study relates to its setting. Indeed, a questionnaire is far removed from the clinical setting. However, responses provided without the stress of a pathological setting could be considered even more accurate than answers given in the stress of a severe trauma assessment. Complementary studies are nevertheless required to avoid this bias. FAST and, more broadly, POCUS aim to clinically interpret the images obtained as part of a comprehensive approach to patient care. In addition, ultrasound is an operator-dependent examination, which gives the questionnaire setting of this study another substantial bias. This bias can be partially attenuated given that the quality of the images was independently and successfully validated by three radiologists.
Another limitation of this work is the selection bias due to the inclusion of physicians registered in the database of two ultrasound training providers in France and Belgium. This does not account for the fact that participants received training in these organizations. Indeed, the mailing lists of the organizations included participants with other courses’ background, although their proportion could not be assessed. Both organizations only offer short ultrasound training programs. The background heterogeneity is therefore substantial in the different subgroups.
Given the COVID-19 crisis, the follow-up email that was initially planned could not be returned by these two organizations.