Liver and biliary tract

Clinical signs of hepatobiliary disease can be nonspecific and include anorexia, apathy, vomiting, diarrhea, polyuria, poly­dipsia, and icterus. The presence of icterus in the absence of anemia indicates hepatobiliary disease in both dogs and cats.

1.3.7.1 Hepatic parenchymal disease

Ultrasonographic changes in patients with hepatic parenchy­mal disorders are generally either focal or diffuse. Diffuse proc­esses are more difficult to recognize than focal or multifocal ones and a change in the echogenicity of the liver is the main ultrasonographic finding. The liver may appear normal or have an increased, decreased, or mixed echogenicity.

In patients with acute liver disease, the liver may appear normal or enlarged with a generalized decrease in echogenic­ity. When the echogenicity is decreased, the portal veins appear much more visible, i.e.

Increased echogenicity of the liver can be detected in a number of conditions including fatty infiltration, steroid hepatopathy, and chronic hepatic diseases, such as hepatitis, cirrhosis, malig­nant histiocytosis, or lymphosarcoma.^41,42,43

Figure 1.34:

Cholangiohepatitis. Ultrasound image of a hypoechoic liver in a 2.5-year-old male Cairn Terrier with icterus and vomiting. The liver is enlarged, hypoechoic, and the portal veins are very prominent and hyperechoic throughout the entire liver. His­topathologic diagnosis: cholangiohepatitis.

Figure 1.35:

Hepatic lipidosis. Ultrasound image of a hyperechoic liver in a 16-year-old, male European short-haired cat that presented with anorexia. The hyperechoic liver (between x-x) is homogenous and few vessels are visible. The echogenicity is equal to or greater than that of the spleen and surrounding mesentery and falci­form fat (F). Note the hypoechoic appearance of the liver dorsally (arrow) due to beam attenuation. Differential diagnoses include hepatic lipidosis, diabetes mel- litus, and neoplasia. Cytologic diagnosis: hepatic lipidosis.

Feline hepatic lipidosis is a common source of intrahepatic cholestasis that can be recognized ultrasonographically (Fig­ure 1.35). The liver of affected cats is enlarged, rounded, shows an increased echogenicity equal to or greater than that of the spleen. In addition, the liver may appear isoechoic or hyper- echoic compared to omental fat and hyperechoic to falciform fat.⁴⁴ Beam attenuation may also occur and the dorsal region of the liver may be difficult to visualize.

Cirrhosis and end-stage chronic inflammatory disease is rare in cats compared to dogs, but hepatic fibrosis may be seen in cats. Hepatic cirrhosis and chronic hepatitis are diffi­cult to diagnose by ultrasound. Furthermore, they can have a similar appearance as neoplastic disease. The liver may be small or normal in size and may contain nodules. Ascites may or may not be present. The nodules tend to be round and distinct and the surrounding liver may be of normal or increased echo­genicity. Ultimately, a biopsy or fine needle aspiration is needed to make a more definitive diagnosis.

In the presence of ascites without venous hepatic conges­tion, spectral Doppler evaluation of the portal vein can be used to rule out portal hypertension. The velocity of the portal venous flow in patients with cirrhosis is generally reduced.⁴⁵ In the presence of portal hypertension and ascites, secondary portosystemic shunts may be detected. Secondary shunts can be recognized by the presence of many tortuous vessels in the abdomen. Doppler ultrasound will show the flow within these vessels to be monophasic and of low velocity, identifying them as portal in origin. In such instances, a surgical mesenteric portogram or a scintigraphic portogram is indicated (Fig­ure 1.36).⁴⁶ Helical CT is a new alternative approach in vet­erinary patients with suspected portosystemic shunts.⁴⁷ Also, contrast harmonic ultrasound has been investigated in dogs for the detection of congenital portosystemic shunts.⁶

Diffuse hepatic changes with mixed echogenicity may also be seen in some patients. Neoplasia is the most common cause when the hepatic parenchyma appears diffusely complex or disrupted with poorly circumscribed areas of both increased and decreased echogenicity. Other possible causes of a com­plex echostructure in the liver are inflammation, toxicity, or

necrosis.

Figure 1.36a-c:

Extrahepatic portosystemic shunts.

(a) Ultrasound image of the liver. The liver was rounded, inhomogeneous, and had an irregular surface.

(b) Numerous aberrant vessels (arrows) with low velocity monophasic flow were identified caudal to the stomach and there was free fluid in the abdomen. Portal venous flow was greatly reduced at only 5 cm/sec. In addition, uroliths were identified in the urinary bladder.

(c) Intraoperative mesenteric venous portogram. Multiple, tortuous shunting vessels (arrows) are shown. A normal portal vasculature could not be demonstrated in this liver. Diagnosis: secondary extrahepatic portosystemic shunts due to chronic liver disease.

Figure 1.37:

Gall bladder wall edema. Ultrasound image of the gall bladder in a 5-month-old mixed-breed dog that presented with weight loss and inappetence of 3 weeks' duration. Serum hepatic enzyme activities and bilirubin concentration were ele­vated and there was a clinical suspicion of hepatitis. Ultrasonographically, the liver was hypoechoic with prominent portal vein walls. The gall bladder showed a “double-walled appearance". The gall bladder wall was 8 mm thick and hypo­echoic with an inner and outer hyperechoic rim. Ascites was also detected. Note that the double-walled appearance in this instance is not due to the presence of ascites since the thickened wall itself can be visualized. Diagnosis: gall bladder wall edema.

Figure 1.38:

Biliary mucocele. Ultrasound image of the gall bladder in an 8-month-old, male Rhodesian Ridgeback that was presented for vomiting of 2 days' duration and a painful abdomen.

Contrast-enhanced ultrasonography has been found to be very useful for differentiating benign from malignant hepatic disease in human beings.^5,48 However, there are few reports describing its use in the assessment of dogs and cats with he­patic disease.

1.3.7.2 Non-obstructive biliary tract disease

Cholecystitis is a form of non-obstructive biliary disease and is usually seen with inflammation due to bacterial infection. The infection may spread to the liver causing cholangiohepa- titis. If the cholecystitis is necrotizing, the infection may even­tually lead to gall bladder rupture and bile peritonitis.

Thickening of the gall bladder wall is a common ultrasono­graphic finding in patients with cholecystitis and cholan- giohepatitis.⁴9 Varying amounts of gall bladder sediment may be identified but this finding is nonspecific. Choleliths and mineralization of the gall bladder wall may also be seen but their significance is dependant on the clinical findings. The thickened wall is generally hyperechoic, possibly with an irregular inner surface. Polyps may occur in patients with chronic cholecystitis and appear as focal or multifocal wall infiltrations or nodules. Neoplasia could have a similar appear­ance, but gall bladder tumors are rare.

The gall bladder may also appear to have two echogenic dou­ble rims with a hypoechoic space in between (Figure 1.37). This double-walled appearance of the gall bladder can be seen with hypoalbuminemia, ascites, sepsis, acute inflammatory dis­ease, or neoplasia.

Emphysematous cholecystitis may be detected radiographi­cally as a zone of hyperlucency in the right cranioventral re­gion of the liver. Ultrasonographically, reverberation echoes either within the gall bladder lumen or the wall may be rec­ognized. This type of “dirty” shadowing can be differentiated from the “clean” shadowing that is seen with calculi in the gall bladder.

Gall bladder mucoceles are important findings in patients with hepatobiliary disease and icterus and various sonographic pat­terns have been described (Figure 1.38).⁵⁰ Gall bladder mu­coceles have the potential to rupture and may cause bile peri­tonitis. In general, the gallbladder wall is thickened and contents with a complex echostructure and echogenicity can be observed. Ultrasonographic evidence of ascites can indicate the presence of rupture and bile peritonitis.

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1.3.7.3 Obstructive disease

Ultrasound can be used to detect dilated and tortuous com­mon and hepatic bile ducts, choleliths, or biliary and peri-bil­iary obstruction. Biliary calculi, pancreatitis, neoplasia, granu­lomas, or abscesses are possible causes of obstruction.⁵¹ Liver flukes in cats are another cause in tropical and subtropical cli­mates. If the patient is anorectic or has been fasted prior to examination, the gall bladder can be very large, which should not be misinterpreted as biliary obstruction. If obstructed, the gall bladder enlarges prior to the intrahepatic bile ducts, which may take days to weeks to dilate. Also, the common bile duct may take days to dilate following obstruction.

The porta hepatis and cranial duodenum can be challenging regions to examine with ultrasound. The presence of food and gas in the gastrointestinal tract is one of the main barriers. With the use of high frequency transducers, however, the du­odenal papilla and bile duct can even be seen in normal dogs and cats (Figures 1.39 a and b). Therefore, visualization of the bile duct should not be considered the sole criterion for bil­iary obstruction. The normal bile duct diameter should not be more than 4 mm in dogs and 3-4 mm in cats.⁵²

Extrahepatic cholestasis can be recognized by a distended gall bladder and bile duct (Figure 1.39 c). The pancreas and duo­denal papilla can be sources of obstruction that can be evalu­ated ultrasonographically (Figure 1.39 d). Pancreatic abscesses, cysts, neoplasia, and choleliths as well as pancreatitis may cause mechanical obstruction of the bile duct (Figure 1.39 e). Bile duct carcinoma, pancreatic carcinoma, or lymphosarcoma in cats are additional causes. Long-standing obstructions may lead to intrahepatic bile duct dilation (Figure 1.39 f ). Ultra­sonographically, “too many vessels” can be visualized in the liver that do not show any blood flow when examined with color Doppler. Differential diagnoses for tubular fluid-filled structures in the liver are obstruction, biliary cysts, pseudocysts, biliary cystadenomas, and bile duct carcinoma.

Nuclear scintigraphy and contrast radiography are not com­monly performed for the diagnosis of hepatobiliary disease in dogs and cats, but quantitative cholescintigraphy can be used to diagnose extrahepatic biliary obstruction.⁵³ Moreover, nu­clear scintigraphy using Tc-99m-mebrofenin shows promise in dogs for the quantification of hepatic function.⁵⁴ Endo­scopic retrograde cholangio-pancreatography (ERCP) uses a combination of endoscopy and fluoroscopy for radiographic contrast imaging of the biliary and pancreatic ducts. Investiga­tors experienced with this method were able to identify an enlarged common bile duct, intraductal filling defects, a devi­ated course of the common bile duct, and a stenosis of the major duodenal papilla in some affected canine patients. This imaging modality requires specialized equipment and training, but may be promising for the diagnosis of biliary and pancre­atic diseases in dogs in the future. ^{55, 56}

1.3.7.4 Interventional procedures of the liver and biliary system

Interventional procedures such as fine-needle aspiration or biopsy of the liver and pancreas can be performed using a 16- to 18-gauge biopsy needle depending on the size of the ani­mal. Both manual and spring-loaded instruments may be used. Recently, the sensitivity and specificity of cytology and histol­ogy of tissue samples collected by fine-needle aspiration has come under criticism.⁵⁷ A coagulation profile should be per­formed prior to percutaneous true-cut biopsy, but it is not necessary prior to fine-needle aspiration unless there is a clin­ical suspicion of a coagulopathy. Complications following liver biopsy are extremely rare. Percutaneous ultrasound-guided cholecystocentesis can be performed for cytologic and bacte­riologic analysis with a high degree of safety in dogs and cats. A 22-gauge, 1.5-inch (3.81-cm) needle with an attached 12-mL syringe is used via a right-sided transhepatic approach. Alternatively, a right ventral abdominal approach into the fun­dus of the gallbladder can be used.⁵⁸

Figure 1.39a-f:

Ultrasonographic assessment of the bile duct.

(a) Normal duodenal papilla in a cat.

(b) Normal common bile duct entering the duodenal papilla in a dog.

(c) Enlarged gall bladder and cystic duct in a dog with extrahepatic bile duct obstruction.

(d) Pancreatitis in a dog that caused obstruction of the bile duct at the duodenal papilla resulting in cholestasis and icterus.

(e) Intraluminal bile concrements obstructing the bile duct in a dog with chronic cholecystitis and choleliths.

(f) Cystic dilation of the intrahepatic bile ducts in a cat with chronic cholestasis due to obstruction of the extrahepatic bile duct.

Figure 1.40a, b:

Acute pancreatitis in a cat.

(a) The right pancreatic limb is enlarged (arrows) and very hypoechoic. The sur­rounding mesenterium is hyperechoic, which is a sign of peripancreatic fat necro­sis. D = duodenum.

(b) The left pancreatic limb in the same cat was smaller but hypoechoic. The pancreatic duct (arrow) is mildly dilated.

1.3.8