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.
Biliary System
Biliary obstruction can be difficult for the novice sonographer to assess. It should be noted that biliary tree distension can mimic other pathology and tortuosity may be a normal variation, especially in cats (Figure 8.15). In cases where biliary obstruction is suspected, it is best to refer for immediate complete detailed abdominal ultrasound to minimize morbidity and the potential for life‐threatening biliary peritonitis, especially when gallbladder rupture is suspected (see Figure 8.14C,D). In cats, a bile duct greater than 4 mm is considered to be consistent with extrahepatic biliary obstruction (d’Anjou 2008) (see also Figure 39.4). In cases where peritonitis is clinically suspected or needs to be ruled out, an AFAST with an abdominal fluid score should be performed and used to guide fine needle aspiration of peritoneal effusion for fluid analysis, cytology and culture (see Chapter 43).
Figure 8.14. Gallbladder mucocele. (A) Gallbladder mucocele in a dog. Note the echostructural appearance of the gallbladder lumen (GB, gallbladder). In real time, mucoceles are typically seen as immobile biliary patterns that have a stellate or fine striated character referred to as the “kiwi fruit” appearance. Also note the typical concurrent distension of the gallbladder that is enlarged because of the mucocele. These findings should prompt a complete evaluation of the peritoneal cavity by AFAST and assignment of an abdominal fluid score to search for any evidence of bile peritonitis (free fluid) secondary to gallbladder rupture, and a thorough abdominal ultrasound interrogation of the entire biliary tract by an experienced sonographer. (B) Additional example of a gallbladder mucocele demonstrating the variability of their ultrasonographic appearance. (C) Ruptured gallbladder secondary to mucocele. When a kiwi fruit‐like structure (*) is not seen associated with the gallbladder and found in any quadrant of the peritoneal cavity, a mucocele may be eviscerated from the gallbladder and freely floating within the abdomen, as shown in this image. Characterization of the abdominal effusion (anechoic in near‐field) as bile peritonitis further supported this clinical suspicion (FF, free fluid; LIV, caudate lobe of liver; RK, right kidney). (D) Ruptured gallbladder secondary to gallbladder mucocele. If the gallbladder is not visualized, or lacks its normal expected curvilinear contour, gallbladder rupture should be suspected. In this image, the dorsal gallbladder wall is deviated from its expected course. Signs of rupture of the gallbladder can also include loculated echogenic fluid within the gallbladder fossa with adjacent hyperechoic reactive mesentery and/or free‐floating shadowing choleliths. Degrees of bile peritonitis (either loculated within the gallbladder fossa or throughout the abdominal cavity) should be present and an AFAST with the assignment of an abdominal fluid score should be performed. Accessible fluid should be aspirated to characterize its nature and direct surgical intervention. Discontinuity of the dorsal aspect of the gallbladder is marked with cursors [<<<]. In cases of gallbladder rupture, emergent exploratory surgery is indicated. Additional, less common rule‐outs for lack of visualization of the gallbladder include gallbladder agenesis (which is rare but has been reported) and obstruction of the cystic duct (such as with a mass lesion), that is impairing normal gallbladder and bile duct filling. Moreover, obscured gallbladder visualization may occur with emphysematous cholecystitis or severe cholelithiasis, warranting the use of radiography.
