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Imaging in Hepatic Disease in Small Animals


Routine abdominal radiographs are useful for determining liver size and may detect irregular liver borders. Mineralized densities involving parenchyma or biliary tree can reflect stasis of bile flow, dystrophic mineralization associated with congenital malformations, acquired duct “sacculation,” chronic duct inflammation, or choleliths. Choleliths containing enough calcium bilirubinate are radiographically visible. A mass effect in the right cranial quadrant in suspected EHBDO may represent an engorged gallbladder, pancreatitis, neoplasia, or focal bile peritonitis. Radiographic suspicion of abdominal effusion (poor abdominal detail) may prompt diagnosis of bile peritonitis. Gas within hepatic parenchyma or biliary structures indicates an emphysematous process (eg, cholecystitis, choledochitis, infected biliary cyst, hepatic abscess, necrotic tumor mass) and warrants prompt antimicrobial therapy, and either surgical intervention or percutaneous ultrasound-guided aspiration/lavage. Thoracic radiography can indicate signs of systemic disease (eg, metastatic lesions, pleural fluid). Sternal lymphadenopathy is common in cats with the cholangitis/cholangiohepatitis syndrome.

Contrast radiographic imaging of the biliary system is rarely pursued. Cholecystography can be accomplished with iodinated contrast given PO or IV. Distribution and concentration of contrast agents within biliary structures is influenced by numerous variables, including hyperbilirubinemia and major duct occlusion. At best, these agents may disclose choleliths, polyps, or sludged bile but are insufficient for confirming bile peritonitis or for localizing the site of leakage. Multisector CT is more useful.

Contrast studies of the portal vasculature are the gold standard for confirmation of a congenital portosystemic shunt. Radiographs should be taken in right and left lateral and ventro-dorsal positions for best test sensitivity. Multisector CT imaging produces exceptional images and is gradually replacing radiographic portography because it allows contrast injection into a peripheral vessel, can capture images within seconds, and allows 3-dimensional anatomic reconstruction.

The numerous diagnostic uses of ultrasonography include: 1) identify distention and determine thickness of biliary structures; 2) verify common bile duct obstruction; 3) detect gallbladder mucoceles and cholelithiasis; 4) differentiate between diffuse and focal hepatic abnormalities; 5) identify and determine dimensions of “mass lesions”; 6) identify pancreatic, mesenteric, and perihepatic lymphadenomegaly; 7) in conjunction with vascular studies, identify congenital intrahepatic and extrahepatic portosystemic vascular anomalies (PSVA), APSS, arteriovenous fistula, and hepatic venule distention consistent with passive congestion; and 8) detect small volume abdominal effusion. However, while abdominal ultrasonography has become an indispensable diagnostic tool for assessment of the liver and biliary system, its use is highly operator dependent, and findings must always be reconciled with the history, physical examination findings, and clinicopathologic data.

Multisector CT imaging, available in specialty referral practices, can distinguish mass lesions, detect changes in structure of hepatic parenchyma and biliary system, identify choleliths, detect abnormal hepatic perfusion (involving the portal vein, hepatic artery, or hepatic vein) and portal thrombi, and can detail the extent of traumatic injuries to the hepatobiliary system.

Last full review/revision March 2012 by Sharon A. Center, DVM, DACVIM

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