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 25-28 September, 2018 | Singapore
WSV18-0037
DIAGNOSTIC IMAGING AND GASTROENTEROLOGY (SIMULTANEOUS TRANSLATION INTO MANDARI
IMAGING PORTOSYSTEMIC SHUNTS IN DOGS: COMPARING RADIOGRAPHY, ULTRASONOGRAPHY AND COMPUTED TOMOGRAPHY
H.G. Heng1
1Purdue University, Department of Veterinary Clincial Sciences, West Lafayette, USA
IMAGING OF PORTOSYSTEMIC SHUNTS IN DOGS: COMPARING RADIOGRAPHY, ULTRASONOGRAPHY AND COMPUTED TOMOGRAPHY
Hock Gan Heng, DVM, MVS, MS, Diplomate ACVR, ECVDI,
Purdue University, Department of Veterinary Clinical Sciences, 625 Harrison Street, West Lafayette, IN 47907, USA.
There are multiple factors that will influence sensitivity and specificity for the diagnosis of intrahepatic and extrahepatic anomalous vesselsin dogs. The 3 most common factors are theavailability of equipment, the operatorand the patient/owner.
Radiography is one of the most commonly use imaging modality for screening of animals with suspected portosystemic shunt. The sensitivity and specificity is low. We may see microhepatia and enlargement of the kidneys. Occasionally, mildly mineralized calculi in the urinary system is visualized. Contrast radiography such as intraoperative cranial mesenteric venography will be able to outline the anomalous vessels, but this is an invasive procedure. Cranial mesenteric angiography which need a fluoroscopy machine is another method of choice. Again this is also an invasive procedure. The advantage of these two procedures are the ability or visualize small intrahepatic portal veins otherwise may not be seen on computed tomography (CT).
Patient preparation for ultrasound is very important in search for both intrahepatic and extrahepatic anomalous vessels. Most of the patient with anomalous vessels has microhepatia, thus it is not easy to visualize the liver
if the patient has excessive movement and panting. Sedating or putting the animal under GA will help to increase the sensitivity of detecting any anomalous vessel. If a patient has a postprandial stomach, this
may reduce the acoustic window and interfering with detection of the normal and abnormal blood vessels. There is variation of the type of the shunt vessels, which include the different sizes and lengths of the anomalous vessel. It is easier to detect a large diameter anomalous vessel, thus the sensitivity and specificity are higher. It
is also easier to trace a short anomalous vessel, and
to be able to recognize the origin and insertion of the anomalous vessel. A small diameter, long and tortuous anomalous vessel could be detected, but most of the time it is difficult to trace the entire vessel. The operator needs to have a very strong knowledge of the normal anatomy of the blood vessels, and also familiar with the various type of anomalous vessels. The last factor is the ultrasound machine used. As a general rule, we need a good ultrasound machines with a better resolution and good Colour Doppler sensitivity to detect any anomalous vessel. This is especially true when the blood vessel(s)
is small. In the last decade, the availablility of better resolution and colour Doppler ultrasound machines and literatures of various anomalous vessels has promote the use of ultrasound in the investigation of intrahepatic and extrahepatic anomalous vessels.
The sensitivity and specificity of ultrasound detection of intrahepatic shunt has been reported to be 100% and 100% while the sensitivity and specificity of detection of extrahepatic shunt has been reported to be 90% and 97% respectively.
There are 2 steps in ultrasonographic examination of the anomalous vessel, the screening and the confirmation.
It has been reported that there is usually a change in size of the blood vessels (portal vein and caudal vena cava) with occurrence of extrahepatic shunt. Thus a comparison of portal vein and caudal vena cava (PV/ CVC), and also portal vein and aorta (PV/Ao) ratio
has been published. A PV/Ao ration of 0.7 to 1.25 is considered normal. Thus, dogs and cats with PV/Ao
ratio of ≤0.65 were found to have either an extrahepatic portocaval shunt or idiopathic, noncirrhotic portal hypertension. Dogs and caats with a PV/Ao of ≥0.80 may have other types of shunts or normal. It is good to use the PV/Ao ratio as a screening procedure before looking for an anomalous vessel. When a patient with a PV/Ao ration of <0.65 and has clinical suspicious of anomalous vessel, the portal vein and caudal vena should be examined carefully. If not anomalous vessel is identified, then abdominal contrast CT is recommended to rule out any small anomalous vessel. If an anomalous vessel is identified ultrasonographically, contrast CT may not be needed.
The anomalous vessel should be classified as congenital or acquired, intrahepatic or extrahepatic, and singular or multiple. Most anomalous vessels are congenital, and singular. Large breed dogs tends to have intrahepatic while smaller breed dogs to have extrahepatic anomalous vessels. In patients with acquired anomalous vessels, this normally occurs secondary to severe
liver disease, hepatic AV malformations, portal vein thrombosis or hepatic vein outflow obstruction with portal hypertension.
There are three types of anomalous vessels in intrahepatic shunts: The left divisional, central divisional
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43RD WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND 9TH FASAVA CONGRESS








































































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