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Evaluation of the luminal gallbladder is typically straightforward due to the ease of scanning through a fluid acoustic window.

 Biliary sediment or sludge is common in dogs and can be easily recognized (Figure 8.12). In general, the finding of gravity‐dependent, mobile material is an incidental finding but could be an indication of cholestasis. Gallbladder wall abnormalities should be correlated to clinical and/or clinicopathological signs of hepatobiliary disease changes (Tsukagoshi et al. 2012). Luminal sediment is usually hyperechoic (bright) and nonshadowing. When mineralized, the debris may cast a distal acoustic shadow (see Figure 8.12D). Biliary sludge is classified as gravity or nongravity dependent and mobile or consolidated. Nongravity‐dependent material may further be classified as adherent or nonadherent to the gallbladder wall.

 Calcified material or choleliths can occasionally be observed within the biliary tract and may also be an incidental finding. These gallbladder stones will cause a distal acoustic shadow similar to a urolith (Figure 8.13; see also 8.12D).

Pearl: When suspicion is raised for intraluminal gallbladder contents, the gallbladder can be reexamined at the end of the study to see if the possible intraluminal pathology has settled into gravity‐dependent regions.

 Gallbladder mucoceles always have significant implications and their presence should be confirmed by an experienced sonographer as surgery is often indicated. Gallbladder mucoceles have a distinct appearance and, in the mature form, have a stellate (“kiwi fruit‐like”) appearance caused by fracture lines between mucous collections (Figure 8.14A,B). When immature, there are variable degrees of nonmobile sludge seen between the focal collections of mucus. In addition, the gallbladder wall may be thickened, irregular and hypoechoic or hyperechoic due to wall inflammation, and may lead to wall necrosis and gallbladder rupture (see Figure 8.14C,D). Six ultrasonographic patterns of mucoceles have been described: type 1, immobile echogenic bile; type 2, incomplete stellate pattern; type 3, typical stellate pattern; type 4, kiwi fruit‐like pattern and stellate combination; type 5, kiwi fruit‐like pattern with residual central echogenic bile; and type 6, kiwi fruit‐like pattern. Based on one study, there was no correlation between the ultrasonographic pattern and clinical disease status or gallbladder rupture (Choi et al. 2014).Figure 8.11. Gallbladder wall abnormalities. (A) Thickened gallbladder wall seen as a hyperechoic (bright white) rim (marked with calipers) outlining the hypoechoic gallbladder (GB) luminal contents. This has been referred to as a double rim effect, halo effect or halo sign and is caused by several conditions. (B) A mildly thickened gallbladder (GB) wall in a cat similarly outlined with a hyperechoic (bright white) line. The caliper measurement is 1.9 mm in thickness, which is considered thickened in cats (normal <1 mm). C) This image is of a dog seen for acute collapse. Note the halo sign hallmarked by the outer and inner hyperechoic borders of gallbladder wall with central hypoechogenicty (intramural edema), termed sonographic striation (white‐black‐white sonographic layering). The thickening of the gallbladder wall is consistent with intramural edema. This case illustrates the value of concurrent evaluation of the pleural and pericardial spaces because the cause of collapse (not always known at triage) was obstructive shock secondary to pericardial effusion and cardiac tamponade and not canine anaphylaxis. Emergent pericardiocentesis is indicated as a life‐saving procedure. Note the small volume of effusion within the gallbladder fossa and ascites (FF, free fluid). (D) The gallbladder double rim effect or halo effect or halo sign, which can range in its degree of gallbladder wall thickness, has been reported to be supportive of anaphylaxis in dogs. This image depicts an acutely collapsed dog diagnosed with anaphylaxis caused by Hymenoptera (bee) envenomation. The gallbladder double rim or halo effect and wall thickening are severe; however, the sonographic striation (white‐black‐white) may be similar and more subtle than shown in (C), emphasizing the importance of the Global FAST approach to avoid “satisfaction of search error.” In contrast to 8.11C, the emergent treatment for anaphylaxis is rapid intravenous fluid bolus and epinephrine administration, emphasizing the importance of surveying the pleural and pericardial spaces in acutely collapsed dogs for optimizing appropriate therapy (see Chapter 8).Source: (C) and (D) courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.Figure 8.12. Degrees of gallbladder sedimentation (sludge). (A) A mild amount of echogenic debris in suspension within the gallbladder lumen with a faint sedimentation line along the gravity‐dependent portion in an asymptomatic dog (GB, gallbladder). (B) Moderate echogenic debris settled within the gravity‐dependent portion of the gallbladder lumen in an asymptomatic dog. (C) Moderate to severe echogenic debris in suspension, some of which is adherent to the gallbladder wall (this is best appreciated in real time). When differentiating sediment (or a thrombus) from a mass, use color flow Doppler for the presence or absence of blood flow. (D) Shadowing (clean shadowing) debris settled within the gravity‐dependent portion of the gallbladder in a dog diagnosed with mineralized biliary sediment, which can be distinguished from a large cholelith by ballottement (agitation) or changes in patient positioning (observing how it moves and resettles into gravity‐dependent regions). Images such as these should prompt a complete detailed abdominal ultrasound evaluation of the hepatobiliary tract and liver when there is biochemical or clinical evidence of hepatobiliary disease.Figure 8.13. Gallbladder stones or choleliths. (A) Two small choleliths in a dog (identified by a small asterisk [*] over each cholelith). The finding was incidental. Note the two linear distal “clean” shadows cast by the small solid structures. These hypoechoic (dark) low‐amplitude echo regions are caused by the highly attenuating mineralized (cholelith) structures (GB, gallbladder). (B) Large, 2 cm cholelith in a dog with biochemical and clinical evidence of biliary obstruction (marked by calipers). Note the strong (anechoic) distal shadow. A complete detailed abdominal ultrasound evaluation of the biliary tract is indicated by a veterinary radiologist or specialist with advanced ultrasound training to best determine biliary tract obstruction. A good rule of thumb when unable to effectively visualize the gallbladder using ultrasound (likely due to mineralized material or air) is to take an abdominal radiograph. (C) Multiple, clean shadowing choleliths demonstrating the variability of size and number identified by a small asterisk (*) over each cholelith. Such findings can be seen incidentally or in patients with clinical evidence of advanced hepatobiliary obstruction. In cases with signs of severe hepatobiliary disease, the entire biliary tract should be evaluated by an experienced sonographer given the potential need for surgical intervention. (D) Example of a shadowing cholelith in a cat. Note the strong clean acoustic shadowing in the far‐field.