Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов
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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.
Figure 8.15. Biliary tract distension. (A) Cat with bile duct tortuosity which can be a normal variant and common finding. This variant can be easily mistaken for a variety of pathology (nodules, cysts, masses) by the novice or hasty sonographer. Careful correlation with other clinical findings is imperative for an accurate assessment (CBD, common bile duct; GB, gallbladder). (B) A cat with suppurative cholangitis with concurrent pathological tortuosity and dilation of the bile duct. The bile duct is seen ventral to the portal vein and can be distinguished from vessels with color flow Doppler evaluation. In cats, a bile duct greater than 4 mm is considered to be consistent with extrahepatic biliary obstruction. When the biliary duct wall is irregular or unevenly thickened, neoplasia should be a differential. (C) Cholelithiasis can be seen anywhere along the biliary tract and presents challenges for the novice sonographer. This image demonstrates a hyperechoic cholelith at the level of the duodenal papilla in a dog. Note the strong distal acoustic shadow (clean shadow) and lack of normal architecture of the duodenal papilla (duod, duodenum). This example emphasizes the need for a complete detailed abdominal ultrasound evaluation by a veterinary radiologist or specialist with advanced ultrasound training.
Routine Add‐on of AFAST and Abdominal Fluid Scoring System (or Global FAST)
In the authors’ experience, it is extremely valuable to perform an AFAST examination with assignment of an abdominal fluid score in either lateral recumbency for the best approach. The positioning of small animals in dorsal recumbency for POCUS abdominal organ exams can obscure small‐volume peritoneal effusion and underestimate the volume of effusion present because peritoneal effusion will flow into the less sonographically accessible diaphragmatic recesses. AFAST improves the diagnostic potential of the ultrasound exam by detecting peritoneal effusion. The early detection of abdominal effusion is clinically important and helps direct additional diagnostic recommendations while avoiding morbidity, complications, and patient mortality in the event the effusion is missed.
The Global FAST approach is used as a screening test to rapidly discriminate between localized and disseminated