Common and Uncommon Errors in Emergency Ultrasound

Abstract

Errors in emergency ultrasound (US) have been representing an increasing problem in recent years thanks to several unique features related to both the inherent characteristics of the discipline and to the latest developments, which every medical operator should be aware of. Because of the subjective nature of the interpretation of emergency US findings, it is more prone to errors than other diagnostic imaging modalities. The misinterpretation of US images should therefore be considered as a serious risk in diagnosis. The etiology of error is multi-factorial: it depends on environmental factors, patients and the technical skills of the operator; it is influenced by intrinsic US artifacts, poor clinical correlation, US-setting errors and anatomical variants; and it is conditioned by the lack of a methodologically correct clinical approach and excessive diagnostic confidence too. In this review, we evaluate the common and uncommon sources of diagnostic errors in emergency US during clinical practice, showing how to recognize and avoid them.

Keywords: B-mode; abdominal trauma; artifacts; diagnostic mistakes; diagnostic pitfalls; emergency; ultrasonography.

Figure 1

The side lobe artifact. (a) Diagram shows multiple beams outside the main US axis encountering an object (yellow box); (b) The display assumes that the return echoes that come from outside the main axis are mistakenly understood as coming from the main axis itself, and therefore misplaces and duplicates the structure (multiple yellow boxes) in the context of the target image. Modified from Feldman MK et al. [5].

Figure 2

Transverse US image of filled bladder shows echoes (a, arrow) in the expected anechoic urine. Transverse US image obtained after optimal placement of the transducer (b) shows resolution of the intra-bladder echoes.

Figure 3

Mirror-image artifact. (a) In this diagram, the gray arrows represent the expected reflective path of the US beam. These echoes are displayed properly. The black arrows show an alternative path of the primary ultrasound beam. It encounters another structure (e.g., a nodular lesion) in its path and is reflected back to the highly reflective surface (e.g., diaphragm). It then reflects back towards the transducer again. (b) The echoes from the deeper reflective interface take longer to return to the transducer and are misplaced on the display. Modified from Feldman MK et al. [5].

Figure 4

Oblique US image obtained at the level of the right hepatic lobe shows a solid-appearing structure posterior to the diaphragm (a, arrow) mimicking lung consolidation (a, star). The presence of a duplicated image of the hepatic vein (b, arrowhead) makes clear this is an artifact and not a real consolidation.

Figure 5

Aorta ghosting. Transverse mesogastric color-Doppler US image obtained at the level of the infra-renal aorta (arrow) shows aorta ghosting (dashed arrows) that projects backwards with the same color sign.

Figure 6

Speed displacement artifact. (a) In this diagram, the blue arrows represent the expected reflected path of the US beam. The red dashed arrows represent the path of an US beam that encounters an area of focal fat travelling slower than in the surrounding tissue. (b) Because the round trip of this echo is longer than expected, the posterior wall is displaced deeper on the display. Modified from Feldman MK et al. [5].

Figure 7

Longitudinal US image of the liver shows that the interface between the liver and the diaphragm (arrow) is discontinuous and focally displaced. This appearance may be explained by areas of focal fat within the liver.

Figure 8

Refraction artifact. (a) Diagram shows the refraction or change in direction of the US beam due to an interface at a non-perpendicular angle. The difference in propagation speed between the two tissues can cause refraction to occur. (b) The object in the path of the refracted portion of the beam is misplaced because the processor assumes a straight path of the beam. Modified from Feldman MK et al. [5].

Figure 9

Coronal images of the left flank. Refraction of the US beam at the lower pole of the spleen causes apparent disruption of the of the middle third of the left kidney (arrows). K: kidney.

Figure 10

Reverberation artifact. (a) Diagram shows ultrasound echoes reflect back and forth between two highly reflective interfaces (“reverberates”) (b) The display shows multiple equally spaced signals extending into the deep field. Modified from Feldman MK et al. [5].

Figure 11

Coronal images of the right kidney. A reverberation artifact from strong echoes of the abdominal wall (arrowhead) projects over the lateral margin of the kidney, mimicking the presence of a subcapsular hematoma (arrows).

Figure 12

Pseudo-fluid produced by adaptive image processing artifact (arrows).

Figure 13

Normal Achilles tendon (a) and anisotropy-related artifact seen at the same tendon (b) that appears hypoechoic (arrows) due to an incorrect angle of the transducer.

Figure 14

Flow sampling error with anomalous steering (a) misinterpreted as occlusion of the internal carotid artery; after steering correction (b) a normal artery patency is evident. False aliasing (c) and its correct setting (d) by changing the detection parameters upwards of the flow rate (yellow box, c,d).

Figure 15

PRF setting. High- (a) middle- (b) and low- (c) PRF setting show progressive better evidence of intra-testicular flow at low setting (yellow box).

Figure 16

Coronal US scan of the left hypochondrium (a) shows a crescent-shaped hypoechoic area misinterpreted as hematoma (arrows) between the surface of the spleen and the left hemidiaphragm in a 25−year-old man investigated for trauma. On CT scan (b) it appears to be a hypertrophy of the left hepatic lobe with splenic kissing (circle).

Figure 17

Transverse US image of the left hypochondrium (a) shows a large hypoechoic area misinterpreted as splenic hematoma (arrows) in a 31-year-old woman investigated for trauma. On CT scan (b) it appears to be a gastric fundus distended by fluid (arrows).

Figure 18

Longitudinal US pelvic scan (a) shows a small, triangular, hypoechoic area which may be misinterpreted as free fluid (arrows). On CT scan (b) it appears to be an intestinal loop (arrows).

Figure 19

Longitudinal US left flank scan (a) shows at the lower pole of the kidney (K) a hypoechoic area which may be misinterpreted as retroperitoneal free fluid (arrows) in a 22-year-old man investigated for trauma. On CT scan (b) it appears to be a spastic intestinal loop (arrow).

Figure 20

Subcostal US right approach (a) shows a hypo-anechoic elongated image (arrow) simulating a small right pleural effusion. Coronal US scan of the left hypochondrium (b) shows a mirror artifact that duplicates the image of the spleen (arrow) and mimics pleural effusion.

Figure 21

(a) Hypoechoic peri-renal fat, (b) peri-pancreatic fat and (c) pericardial fat misinterpreted as fluid collections (arrows). (d) On CT scan pericardial fat was clearly visible without any fluid collection (star) unlike what was wrongly diagnosed on US scan (c). P: pancreas.

Figure 22

Transverse US scan of the epigastrium (a) shows a focal thickening of the aortic wall (arrow) misinterpreted as hematoma in a 45-year-old man investigated for high-dynamic deceleration trauma. On CT scan (b) it appears to be a hypertrophic right diaphragmatic pillar (arrow).

Figure 23

Transverse US scan of the bladder (a) shows a diffuse thickening of the wall (arrow) in a 78-year-old man investigated for hematuria. On CT scan (b) it appeared to be a large blood clot occupying the entire lumen of the bladder (arrowheads).

Figure 24

Longitudinal US B-mode (a) and color-Doppler (b) scan of the inguinal canal show a blockage of the inguinal canal misinterpreted as an inguinal hernia with congested intestinal loop. On CT scan (c) it appears to be a right epididymitis with funiculitis.

Figure 25

Rouleaux formation over the venous valves (a, arrows). After distal compression, the blood was squeezed and the rouleaux was finally cleared (b,c).

Figure 26

Coronal US scan of the left hypochondrium (a) shows partial exploration of the spleen with unrecognized traumatic injury (arrow) in a 22-year-old man investigated for trauma. On CT scan (b) it appears to be more evident (arrow).

Figure 27

Coronal US scan of the left hypochondrium (a) is strongly influenced by the breakage of the probe crystals (arrows) and does not clearly show the large splenic hematoma. On CT scan (b) the splenic hematoma appears to be more evident (arrows).