(Radiology. 2000;214:881-882.)
© RSNA, 2000
The WES Sign1
Frank J. Rybicki, MD, PhD
1 From the Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115. Received May 1, 1998; revision requested July 6; revision received September 22; accepted January 19, 1999. Address reprint requests to the author (e-mail: rybicki@bwh.harvard.edu).
Index terms: Gallbladder, calculi, 762.286, 762.289 • Gallbladder, US, 762.12981, 762.12989, 762.2897 • Gallbladder, wall thickening, 762.2897 • Signs in Imaging
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APPEARANCE
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The ultrasonographic (US) wall echo shadow (WES) sign occurs in the gallbladder fossa. It is characterized by two curvilinear, parallel echogenic lines separated by a thin hypoechoic space and acoustic shadowing distal to the echogenic line in the far field (Fig 1a).
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Figure 1a. Gallbladder containing a single large stone demonstrates the WES sign. (a) Sagittal US scan obtained with a 5.0-MHz transducer shows the wall (arrows) as a curvilinear echogenicity in the near field. Gallstones form the far field curvilinear echogenicity, or echoes (arrowhead). The S marks the area of prominent posterior acoustic shadowing that results from sound attenuation caused by the calculi. (b) Unfixed pathologic gallbladder specimen photographed before decalcification shows the gallbladder wall (arrow), an intervening space that contained bile in vivo, and a large gallstone (asterisk). (c) Sagittal US scan obtained with a 3.5-MHz transducer. At this lower frequency, the gallbladder wall is not resolved from the underlying stones.
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Figure 1b. Gallbladder containing a single large stone demonstrates the WES sign. (a) Sagittal US scan obtained with a 5.0-MHz transducer shows the wall (arrows) as a curvilinear echogenicity in the near field. Gallstones form the far field curvilinear echogenicity, or echoes (arrowhead). The S marks the area of prominent posterior acoustic shadowing that results from sound attenuation caused by the calculi. (b) Unfixed pathologic gallbladder specimen photographed before decalcification shows the gallbladder wall (arrow), an intervening space that contained bile in vivo, and a large gallstone (asterisk). (c) Sagittal US scan obtained with a 3.5-MHz transducer. At this lower frequency, the gallbladder wall is not resolved from the underlying stones.
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Figure 1c. Gallbladder containing a single large stone demonstrates the WES sign. (a) Sagittal US scan obtained with a 5.0-MHz transducer shows the wall (arrows) as a curvilinear echogenicity in the near field. Gallstones form the far field curvilinear echogenicity, or echoes (arrowhead). The S marks the area of prominent posterior acoustic shadowing that results from sound attenuation caused by the calculi. (b) Unfixed pathologic gallbladder specimen photographed before decalcification shows the gallbladder wall (arrow), an intervening space that contained bile in vivo, and a large gallstone (asterisk). (c) Sagittal US scan obtained with a 3.5-MHz transducer. At this lower frequency, the gallbladder wall is not resolved from the underlying stones.
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EXPLANATION
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The anatomic basis of the WES sign is the well-defined echogenic gallbladder wall (W), echoes (E) from gallstones located immediately beneath the gallbladder wall, and prominent posterior acoustic shadowing (S) that results from sound attenuation caused by the calculi. The hypoechoic region between the echogenic gallbladder wall and subjacent calculi represents a thin layer of interpositioned bile (Fig 1).
When the findings of the WES sign were described in the early 1980s, two groups reported different anatomic explanations, the discrepancy being in the identification of the gallbladder wall. In one report (1), the findings were described as the "WES triad," and the gallbladder wall was claimed to be in the hypoechoic space between the curvilinear parallel echogenic lines. In the second report (2), the findings were called the "double-arc-shadow sign," the gallbladder wall was identified as the echogenic curvilinear line in the near field, and the hypoechoic space was attributed to interpositioned bile. Most likely, the discrepancy between the two reports was secondary to the relatively poor resolution of the available US equipment.
As higher frequency transducers were developed, the resolution of the two curvilinear parallel echogenic lines of the WES sign improved. A normal gallbladder wall consists of a well-defined echogenic line; with gallbladder wall thickening this line often appears as two echogenic lines separated by a relatively hypoechoic space (3).
Between the echogenic gallbladder wall and the echoes originating from the gallstones is a thin and often irregularly contoured hypoechoic area that represents bile within the gallbladder lumen (Fig 2). The contour usually appears irregular because of the passive nature of bile as it intersperses between multiple stones. Less common is the case of a single large stone, in which the hypoechoic area between it and the gallbladder wall is smooth.
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Figure 2. Sagittal US scan of a gallbladder that contains multiple stones
demonstrates the common appearance of the WES sign. The wall (arrows) is represented by the curvilinear echogenicity in the near field. The gallstones form the far field curvilinear echogenicity, or echoes (arrowhead). The S marks the area of prominent posterior acoustic shadowing that results from sound attenuation caused by the calculi. The irregularly contoured hypoechoic area between the echogenic wall and the echogenic gallstones represents passive interspersed bile.
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DISCUSSION
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Recognizing the WES sign is important for two reasons. First, this sign suggests that either a large gallstone (Fig 1a) or multiple small stones (Fig 2) have filled the gallbladder lumen, despite the fact that the gallbladder is not completely visualized. Second, if the WES sign is not recognized, an abnormal gallbladder may be misinterpreted as a loop of bowel.
In most cases, the appearance of the WES sign is sufficiently clear to make a confident diagnosis of cholelithiasis. Occasionally, however, instead of detecting two parallel curvilinear echogenic lines, one may see only a single line. In some patients, this is due to calcification within the gallbladder wall (ie, porcelain gallbladder); in others, it may relate to a technical problem that is causing poor axial resolution (Fig 1c). The image in Figure 1c was obtained with a 3.5-MHz transducer and shows only a single echogenic line in the near field, with prominent acoustic shadowing. To improve resolution, an additional US scan was obtained by using a 5.0-MHz transducer (Fig 1a). The image in Figure 1a, the technically superior scan, demonstrates the WES sign and thus led to the correct diagnosis of cholelithiasis.
Another potential pitfall that can mimic the WES sign occurs when a pathologically or physiologically contracted gallbladder is ultrasonographically nonvisible. In this situation, a portion of the duodenum can occupy the gallbladder fossa. When this occurs, echoes from the duodenal wall can resemble the gallbladder wall, while air within the duodenum appears echogenic and is associated with distal shadowing. In these patients, real-time US scanning may demonstrate visible bowel peristalsis with close observation. However, in questionable cases, the patient should drink a glass of water while repeated real-time US imaging is being performed to distinguish bowel from cholelithiasis.
In almost all cases, the WES sign permits a confident diagnosis of cholelithiasis. Although similar findings in the gallbladder fossa may occasionally be secondary to a porcelain gallbladder or an interposed loop of bowel, appropriate technique should eliminate these diagnostic errors.
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Acknowledgments
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I gratefully acknowledge the invaluable assistance of Faye C. Laing, MD.
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Footnotes
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Abbreviation: WES = wall echo shadow
A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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MacDonald FR, Cooperberg PL, Cohen MM. The WES triad: a specific sonographic sign of gallstones in the contracted gallbladder. Gastrointest Radiol 1981; 6:39-41.[Medline]
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Raptopoulos V, D'Orsi C, Smith E, Reuter K, Moss L, Kleinman P. Dynamic cholecystosonography of the contracted gallbladder: the double-arc-shadow sign. AJR Am J Roentgenol 1982; 138:275-278.[Abstract/Free Full Text]
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Wegener M, Borsch G, Schneider J, Wedmann B, Winter R, Zacharias J. Gallbladder wall thickening: a frequent finding in various nonbiliary disorders—a prospective ultrasonographic study. J Clin Ultrasound 1987; 15:307-312.[Medline]
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