Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов
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acoustic enhancement, side‐lobe artifact, edge shadowing artifact, and mirror image artifact (when the gallbladder contacts the diaphragm–lung interface).
Gallbladder Wall
Evaluation of the gallbladder wall is generally easily accomplished due to the contact between the anechoic bile and the more echogenic gallbladder wall and surrounding hepatic parenchyma. The normal gallbladder wall appears as an echogenic (white) line surrounding the luminal contents (see Figure 8.4A–C). Diffuse gallbladder wall thickening may occur with a wide range of conditions such as acute or chronic cholecystitis, hepatitis, canine anaphylaxis (Quantz et al. 2009), right‐sided heart failure, iatrogenic volume overload (Nelson et al. 2010), and hypoalbuminemia (Nyland et al. 2002) (see Chapters 7, 20, 26, and 36). Therefore, the finding must be interpreted in conjunction with additional ultrasound findings as well as clinical signs and biochemical alterations (Figure 8.11; see also Figures 7.11, 7.12, 18.22, and 39.6).
Generally, gallbladder wall thickening is nonspecific for any of the above conditions and thickening is typically associated with wall edema with similar sonographic features despite the underlying pathologic cause (see Figure 8.11 and Table 7.5). Most commonly, the gallbladder wall appears diffusely hypoechoic with parallel hyperechoic lines on either side, referred to as a “double rim effect” or “halo effect” (Nyland et al. 2002; Quantz et al. 2009) (see Figures 7.11, 7.12, 18.22, and 39.6). This change needs to be distinguished from small‐volume fluid external to the gallbladder, where effusion within the gallbladder fossa can mimic the double rim or halo effect. Focal and/or irregular thickening of the gallbladder wall is less common, and may be consistent with chronic cholecystitis or neoplastic change. A flaccid or undulating gallbladder wall may be consistent with wall rupture and warrants correlation to the index of suspicion for biliary peritonitis as well as clinical and biochemical assessment of the patient.
Pearl: In patients in which peritonitis is suspected (ruptured gallbladder, perforated bowel, low‐grade bleed), especially in dehydration, fluid resuscitation and reevaluation (serial exam within the next 2–4 hours) with AFAST and an abdominal fluid score often prove most helpful because once rehydrated, peritoneal effusion develops or progresses (higher abdominal fluid score) and sampling for fluid characterization becomes possible.
Gallbladder Lumen
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)