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Liver

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Abstract

Ultrasonography is an essential imaging and screening method in animals with suspected liver disease, including vascular anomalies. Indications include: clinical signs or biochemical changes associated with liver disease; icterus; ascites; pyrexia of unknown origin; cranial abdominal mass; cranial abdominal pain; and to search for metastatic disease when a primary tumour has been found elsewhere. This chapters explores the value of ultrasonography compared with radiography and computed tomography. Imaging technique and normal ultrasonographic appearance are addressed. Diffuse parenchymal disease; focal parenchymal disease; biliary tract conditions; vascular abnormalities and considerations for sampling are covered. This chapter contains five video clips.

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Figures

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8.1 Longitudinal image of the normal liver in a dog. Note the liver parenchyma (*) is displayed distal to the hyperechoic diaphragm as a result of a ‘mirror image’ artefact. Longitudinal image of the left side of the normal liver in a dog. Note the caudal location of the stomach (ST) and the hyperechoic interface of the diaphragm (arrowed).
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8.2 Transverse ultrasonogram of the normal liver in a dog showing the coarse echotexture of the falciform fat (*) compared with the liver. Note the hyperechoic interface (arrowed) marking the separation between the liver and ventrally located falciform fat, which can be mistaken for an enlarged liver. The liver is of normal size and echogenicity.
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8.3 Longitudinal ultrasonogram of the normal liver (L). The liver appears more hypoechoic and coarse in echotexture compared with the spleen (S). This is due to the presence of the hepatic and portal veins.
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8.4 Longitudinal ultrasonogram of the liver in a cat. The gallbladder is bilobed and appears heart-shaped. This is an incidental finding in cats. Note also the acoustic enhancement distal to the gallbladder (*), which is due to lower attenuation from the bile and should not be confused with a hyperechoic lesion. The liver is diffusely hyperechoic due to the presence of hepatic lipidosis. Transverse ultrasonogram of a gallbladder in a dog. Note the hyperechoic sludge (*) in the dependent part of the gallbladder. Ultrasonogram of the normal liver in a dog. The gallbladder (GB) is seen with anechoic content and thin walls, which are barely visible. Note the hyperechoic walls of the portal veins (arrowed).
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8.6 Ultrasonogram of a dog with hypoglycaemia and in hypovolaemic shock. Note the diffusely hypoechoic liver with prominent hyperechoic portal vessel walls, consistent with hepatitis. Ultrasonogram of a dog with pancreatitis and elevated liver enzymes. Note the thick-walled portal vessels and diffusely hypoechoic liver, consistent with cholangiohepatitis.
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8.7 Ultrasonogram of the liver in a dog with chronically elevated liver enzymes for the past year. Note the irregular border of the liver and heterogeneous parenchyma. The surrounding mesentery appears hyperechoic. This finding is suggestive of liver fibrosis or cirrhosis.
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8.8 Hepatic ultrasonogram of a dog with chronic skin lesions. Note the diffusely hypoechoic foci surrounded by hyperechoic parenchyma resembling a honeycomb or Swiss-cheese pattern, commonly seen with hepatocutaneous syndrome.
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8.9 Hepatic ultrasonograms of confirmed lymphoma. The liver appears diffusely hypoechoic with prominent portal markings. Diffuse hyperechoic liver with loss of vessel demarcation and irregular organ margins. Hyperechoic well defined mass within the liver parenchyma.
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8.10 Ultrasonogram of a dog with elevated liver enzymes. The liver appears diffusely hyperechoic with loss of vessel wall distinction. Cytological diagnosis was hepatopathy with glycogen accumulation.
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8.11 Ultrasonogram of the liver in an obese cat with diabetes mellitus and hepatic lipidosis diagnosed with FNA. The liver is markedly hyperechoic in the near-field. Note the decreased echogenicity in the far-field due to beam attenuation; this is commonly seen in cats with hepatic lipidosis.
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8.12 Ultrasonogram of a dog with histological confirmation of vacuolization and regeneration. The liver appears diffusely hyperechoic with loss of vessel wall distinction and multifocal hypoechoic lesions (*). The stomach (ST) is seen caudally.
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8.13 Ultrasonogram of a dog with histological confirmation of a hepatocellular carcinoma. Note the well defined hypoechoic nodules, partially protruding beyond the liver surface (arrowed). Multifocal target lesions (*) are seen with a hyperechoic centre and a hypoechoic rim.
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8.14 Longitudinal ultrasonogram of the liver in a dog with a congenital extrahepatic shunt and elevated bile acids. Note the small liver with the stomach (ST) being closer to the diaphragm (arrowed) than usual.
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8.15 Ventrodorsal radiograph of the cranial abdomen in a dog with lethargy, anorexia and fever. Radiolucent gas bubbles are present within the liver parenchyma cranial and medial to the stomach (between the arrows), consistent with a cavitary hepatic lesion such as a liver abscess. Lateral radiograph showing the radiolucent gas bubbles (arrowed) in the liver. Ultrasonogram of the lesion showing the well defined hypoechoic area (between the callipers) and the hyperechoic areas with dirty shadowing consistent with gas inclusion. The cytological diagnosis confirmed a liver abscess.
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8.16 Ultrasonogram of the liver in a dog with histological confirmation of a hepatocellular carcinoma. Note the multifocal hypoechoic lesions throughout the liver parenchyma. Contrast-enhanced harmonic ultrasonogram of the liver following intravenous injection of contrast medium. Note the multifocal hypoperfused well defined areas consistent with a malignant hepatocellular carcinoma.
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8.17 A variety of ultrasonographic changes are associated with histiocytic sarcoma. A cat with a well defined hypoechoic nodule within the otherwise hyperechoic liver. A dog with target lesions within the liver.
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8.18 Ultrasonogram of the liver in a dog with multifocal hypoechoic nodules. The liver is diffusely hyperechoic. Hepatopathy with vacuolization and regeneration was diagnosed on FNA. Contrast-enhanced harmonic ultrasonogram following injection of microbubble contrast medium. The liver appears generally hyperechoic without evidence of nodules consistent with nodular hyperplasia.
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8.19 Ultrasonogram of the liver in a dog. In the left liver lobe an anechoic, round, thin-walled structure (*) with distal acoustic enhancement was found. This was considered an incidental finding and a liver cyst was diagnosed.
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8.20 Ultrasonogram of the liver in a dog showing accumulation of a round structure (*) within the gallbladder isoechoic to the liver parenchyma with no evidence of distal shadowing, indicating no mineralization (sludge ball). Ultrasonogram of a sludge ball (between the callipers) in the lumen of the gallbladder in a dog. The structure is hyperechoic in comparison with the liver parenchyma. Note the lack of distal acoustic shadowing.
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8.21 Ultrasonogram of the gallbladder in a dog. The curvilinear structures with distal shadowing (arrowed) in the gallbladder lumen representing choleliths. Note the diffuse thickening of the gallbladder wall. Ventrodorsal radiograph of a cat. Note the mineral opaque material (*) consistent with sand in the gallbladder. Ultrasonogram of the gallbladder of the cat in (b). Note the hyperechoic line with marked distal shadowing (*) in the gallbladder lumen representing accumulation of dense sludge, likely containing crystals. The material was swirling and mobile with positional changes of the patient.
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8.22 Ultrasonograms of the liver in an icteric cat with elevated liver enzymes. Note the anechoic free fluid in the abdomen and the marked dilatation of the common bile duct (*). The common bile duct ends abruptly and a hyperechoic round mass is seen in between the arrows. Magnified image of the mass in the common bile duct showing extrahepatic cholestasis.
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8.23 Ultrasonogram of the gallbladder in a dog. Note the concentric layered thickening of the gallbladder (‘double gallbladder wall’), which can be observed in cases of peritoneal effusion, oedema or inflammation.
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8.24 Ultrasonogram of the gallbladder in a dog showing a mucocele. The gallbladder contains hyperechoic striations in an organized pattern resembling the cut surface of a kiwi fruit. Note the hypoechoic rim representing mucin in between the wall and the mucocele.
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8.25 Gallbladder mucocele in different dogs showing the various types of pattern that can be observed on ultrasonographic examination.
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8.26 Ultrasonogram of the liver in a dog presented for vomiting. The gallbladder (*) contains some hyperechoic sludge and a thickened wall. Note the asymmetric fluid accumulation surrounding the gallbladder (arrowed). Gallbladder wall necrosis and rupture were diagnosed during surgery.
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8.27 Ultrasonogram of the liver in a dog in right heart failure. Note the anechoic abdominal effusion (O). The liver is enlarged and the hepatic veins and caudal vena cava (*) are severely distended.
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8.28 Ultrasonograms of the liver in a 9-month-old Labrador Retriever with elevated bile acids. A large vessel connecting the portal vein with the caudal vena cava (CVC) is visible. The CVC is markedly distended. Diagnosis was a single congenital intrahepatic PSS. Transverse view of the liver showing the enlarged CVC with the termination of the large intrahepatic shunt (*).
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8.29 Ultrasonograms of the liver in a 10-month-old Maltese mixed-breed dog with central neurological signs. A large tubular vessel (*) is visible originating from the portal vein. A single congenital extrahepatic shunt was diagnosed and confirmed on surgery. The large vessel connecting to the caudal vena cava (between the callipers) is visible.
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8.30 Spectral Doppler ultrasonograms of the liver in a 5-year-old Golden Retriever with a 4-month history of weight loss and lethargy after heartworm treatment. Reduced blood flow velocity of 10 cm/s is evident in the portal vein consistent with portal hypertension. Multiple enlarged tortuous vessels are identified caudal to the left kidney and outlined with power Doppler.

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Hepatocellular carcinoma with contrast.

Longitudinal image of the liver of the same dog as in Figure 8.16 during a contrast-enhanced ultrasound examination. Forty seconds after injection of the contrast medium, rounded hypoechoic areas are seen within the parenchyma, resembling the hypoechoic areas seen on routine ultrasonography. This is consistent with a malignant lesion and the final diagnosis was a hepatocellular carcinoma.

Hepatopathy with contrast.

This clip shows a longitudinal image of the liver of the same dog as in Figure 8.18. Initially the image appears very dark. After the initial arterial phase, homogeneous enhancement of the surrounding liver parenchyma occurs.

Obstructive cholestasis.

This clip shows an ultrasound examination of the cranial abdomen of the same cat as in Figure 8.22. An anechoic tubular structure is seen running transversely across the image; this is a massively distended common bile duct. Multiple hyperechoic plugs are seen with the bile duct, resulting in obstruction. An irregularly enlarged hypoechoic pancreas is seen lying adjacent to the bile duct (to the right) with hyperechoic surrounding fat. These findings are suggestive of pancreatitis.

Hepatic venous congestion.

This clip shows the liver of the same dog as in Figure 8.27 using Colour Doppler with the sample volume placed in the caudal vena cava. The liver is enlarged and the caudal vena cava and hepatic veins are distended. Turbulent blood flow is seen in the caudal vena cava as a mosaic of colours.

Portosystemic shunt.

Ultrasound examination of the cranial abdomen of a 10-month-old Maltese mixed-breed dog with neurological clinical signs. The clip initially shows an anechoic tubular structure running transversely across the image, which is the portal vein. The liver in this dog is very small; the stomach is visible to the left of the image. Towards the end of the clip, a large tubular vessel can be identified originating from the portal vein and running deep to it to join the caudal vena cava. A single congenital extrahepatic shunt was diagnosed and confirmed at surgery.

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