The liver and gallbladder

image of The liver and gallbladder
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The canine and feline liver consists of six lobes with several processes. In dogs and cats the liver is located within the ribcage. The convex diaphragmatic surface of the liver is intimate with the concave visceral surface of the diaphragm. The visceral surface of the liver contains impressions of the adjacent organs (gallbladder, right kidney, stomach and duodenum). The strong lobation and a small film of peritoneal fluid provide high flexibility to accommodate the respiratory excursion of the diaphragm. The gallbladder is a pear-shaped fluid-filled organ located between the quadrate and right medial liver lobes in the dog and between two parts of the right medial liver lobe in the cat. It stores and concentrates the bile that it receives from the hepatic biliary ducts. Bile is secreted into the duodenum via the cystic and common bile duct. The anatomy of the bile duct and its relationship with the pancreatic duct differs between dogs and cats. In cats, the gallbladder is frequently bilobed. The chapter looks at Radiographic anatomy and normal variation; Significance of radiographic abnormalities; Ultrasonography; and an Overview of additional imaging modalities.

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12.1 Visceral surface of the canine liver and gallbladder. The liver consists of six different lobes. The caudate lobe contains the papillary process (PaPr) centrally and the caudate process (CaPr) and renal fossa (ReFo) (for the right kidney) on the right. The porta hepatis is the central hilus of the liver, which allows passage of the hepatic artery (HA), portal vein (PV), caudal vena cava (CVC), common bile duct, nerves and lymphatics. The gallbladder (GB) is adjacent to the right medial and quadrate lobes. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and are printed with her permission.
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12.2 Feline and canine bile and pancreatic duct systems. The gallbladder receives bilious secretions from numerous hepatic bile ducts (Hep D) via the cystic bile duct (CyBD). Bile is excreted into the duodenum via the cystic and hepatic bile duct(s) which, after receiving the last tributary, form the common bile duct (CBD). The CBD is more tortuous in the cat. The CBD drains into the proximal descending duodenum at the major duodenal papilla. In the dog this entrance is shared with the pancreatic duct (PD), whereas in cats the PD joins the CBD before entering the sphincter. The canine pancreas has an additional larger accessory pancreatic duct (Acc PD), which drains into the minor duodenal papilla further distally into the duodenum, whereas only 20% of cats have this duct and papilla. Variations have been described in both species.
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12.3 Normal hepatic silhouette of a deep-chested 2-year-old Boxer on a left lateral radiograph. The caudoventral hepatic margin is contained within the ribcage. The gastric axis (blue line) connecting the centres of the gastric fundus and pyloric antrum (dashed circles) is oriented within a normal range from parallel to the ribs to perpendicular to the lumbar spine (green lines). Normal hepatic silhouette of a barrel-chested 6-year-old West Highland White Terrier on a right lateral radiograph. The gastric axis (blue line) is parallel to the ribs and the caudoventral hepatic margin (green line) is sharp and at the level of the costal arch. Close-up of a VD radiograph of the same dog as in (b). The liver is symmetrically distributed throughout the cranial abdomen and is bordered by the gas-filled gastric fundus (F) and cranial duodenal flexure (D). Close-up of a VD radiograph of an 8-year-old Turkish Angora cat. Owing to large amounts of peritoneal fat, the liver margins are more visible than those in (c), and the right side protrudes further caudally than the left. (Courtesy of J Drees). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and are printed with her permission.
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12.4 Close-up of a lateral radiograph of a 12-year-old mixed breed dog with hepatocellular carcinoma and radiographic abnormalities in liver shape. The gas-filled stomach is bent around the curved liver margin and the caudoventral hepatic margin is blunted.
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12.5 Close-up of a lateral radiograph of a 10-year-old Cavalier King Charles Spaniel with biliary tree mineralization. Such opacities are occasionally seen incidentally in small-breed dogs but may be associated with chronic disease and bile obstruction. Close-up of a lateral radiograph of an 8-year-old Old English Sheepdog with a metallic hepatic foreign body that presumably penetrated the liver via the gastric wall. Close-up of a lateral radiograph of a 12-year-old Golden Retriever with a hepatocellular carcinoma that was treated with chemoembolization, chemotherapy and intra-arterial ethiodol. Ethiodol is a lipid-based contrast medium that remains radiographically evident for several weeks as a diffuse mineral opacity. Close-up of a lateral radiograph of a 10-year-old Domestic Shorthaired cat with emphysematous cholecystitis. Note the irregular gas opacity (arrowheads) in the region of the gallbladder. Close-up of a lateral radiograph of a 9-year-old German Shepherd Dog with pneumoperitoneum caused by a recent laparotomy (normal finding). The surrounding gas makes the liver and gallbladder (G) much more discernible. Separation of the diaphragmatic and hepatic silhouettes (arrowheads) is a hallmark for even small amounts of free peritoneal gas. Unless there is a benign explanation, free peritoneal gas constitutes a surgical emergency.
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12.6 Close-up of a right lateral radiograph of a dog with microhepatia. Although the fluid-filled pylorus is difficult to discern, the gastric axis can be seen to be rotated in an anticlockwise direction beyond a line perpendicular to the lumbar spine.
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12.7 Close-up of a lateral radiograph of a 14-year-old Jack Russell Terrier with generalized hepatomegaly associated with hyperadrenocorticism. The gastric axis is rotated clockwise beyond being parallel with the rib, and the caudoventral hepatic margin is protruding into the mid-abdomen. Generalized hepatomegaly is a non-specific radiographic finding.
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12.8 VD abdominal radiograph of a 7-year-old Cocker Spaniel with caudate liver lobe torsion. The pyloric antrum (P), duodenum and ascending colon (white/black arrowheads) are displaced towards the median plane by the enlarged lobe. The left caudal hepatic margin, outlined by the gastric fundus (F), remains normal. There are small gas bubbles within the mass attributable to central necrosis (arrowed).
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12.9 Lateral radiograph of a 2-year-old Domestic Shorthaired cat with pyothorax. The hepatic silhouette is not enlarged but the liver is displaced caudally by the space-occupying pleural effusion.
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12.10 Close-up of a right lateral radiograph of a 3-month-old Boxer with right hemidiaphragmatic paralysis. Note the cranial location of the caudoventral hepatic margin (green line). This position was not caused by microhepatia but by cranial displacement of the flaccid right hemidiaphragm (red line).
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12.11 Close-up of a lateral radiograph of a 13-year-old Domestic Shorthaired cat with mineralization of the hepatic biliary ducts and the extrahepatic common bile duct (arrowheads), leading to biliary obstruction and cholangitis. Close-up of a lateral radiograph of a Siamese cat with gallbladder mineralization without clinical signs. The cast-like mineralization could be caused by numerous, small radiopaque choleliths or by gallbladder wall mineralization.
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12.12 Mid-sagittal ultrasonogram of the normal liver in a cat. The liver margins are outlined with arrows.
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12.14 The normal echogenicity of the canine and feline liver (L) is often higher than that of the right renal cortex (K) and less than that of the spleen (S). In a hypoechoic liver the margins of the portal vasculature often stand out as being particularly bright, whereas in hyperechoic liver tissue these margins blend in with the parenchyma. Mixed echoic pattern with Swiss cheese-like hypoechoic nodules and hyperechoic surroundings in a dog with hepatocutaneous syndrome. Multiple hypoechoic hepatic nodules diagnosed as benign hyperplasia on a fine-needle aspirate. Feline biliary cystadenoma in the left lateral liver lobe with multiple anechoic cystic structures and distal enhancement.
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12.15 Hyperechoic sludge is an incidental finding in the canine gallbladder. Note the interface between the echoic and anechoic bile, which was parallel to the decubital plane of the dog.
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12.16 Large mineralized gallbladder calculus with distant shadowing in a dog. This was an incidental finding. Hyperechoic partially thickened gallbladder wall associated with wall mineralization in the same cat as in 12.11b. This was an incidental finding. Partially hyperechoic non-mineralized gallbladder wall (no distant shadowing) in a dog. This was an incidental finding.
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12.17 Thickened canine gallbladder wall with a layered appearance (hypoechoic central layer) indicative of mural oedema, commonly seen in cholecystitis.
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12.18 Short axis view of the gallbladder of a 13-year-old English Springer Spaniel with a gallbladder mucocele. Note the spoke-like hyperechoic lines that resemble the cut section of a kiwi fruit ( or ). Long axis view of the gallbladder of a 13-year-old English Springer Spaniel with a gallbladder mucocele.
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12.19 CT image of the liver of an 11-year-old Afghan Hound that had received intravenous ionic iodinated contrast medium 1 hour earlier. Contrast-enhanced bile can be seen within the ducts and the gallbladder. This was an incidental finding. Hypoattenuating lesion, which was diagnosed as benign hyperplasia, in the left lateral liver lobe after administration of intravenous contrast medium to a 9-year-old Jack Russell Terrier. Image of the liver during the portal phase of CT angiography in a 6-month-old Shi Tzu without evidence of a macroscopic portosystemic shunt. There is a marked perivascular halo around the portal vein branches and the caudal vena cava, consistent with perivascular oedema, a non-specific sign of hepatopathy.
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