Portosystemic Shunts - The University of Tennessee College of ...

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“If no shunting is seen on CT or scintigraphy and the liver biopsy ispositive for MVD, then the dog has PVH-MVD.”—TobiasWhat is Scintigraphy?What is a Portogram?What is a CT Scan?Scintigraphy is a nuclear scan that measures blood flow. To evaluate adog for a shunt, a radioactive material is inserted into the colon (by ahigh enema) or injected into the spleen (“trans-splenic” scintigraphy),and a special camera is used to measure the amount of radioactivity inthe dog’s heart and liver. Trans-splenic scintigraphy produces a betterimage and uses less radioactive material, so it is preferred over colonicscintigraphy. In a normal dog, over 95% of the radioactive materialinjected into the spleen will head to the liver; if more than 5% goes tothe heart, a shunt is diagnosed. Scintigraphy is safe and quick but doesrequire heavy sedation or anesthesia. Small dogs can often be releasedfrom the hospital on the same day of trans-splenic scintigraphy, butlarger dogs and those with multiple acquired shunts usually need to stayovernight until they have expelled the radioactive material by defecationand urination. Scintigraphy tells us that shunting is present and oftenlets us know if the shunts are congenital or acquired, but it does not tellus whether the shunt is inside or outside of the liver.A portogram is an X-ray of the blood vessels to the liver. Because bloodvessels are not easily seen on regular x-rays, a contrast material (a liquidthat looks white on X-rays) must be injected into a blood vessel in theabdomen. The injection can be performed through a surgical incisioninto the belly; by injecting the spleen directly through the skin; or bypassing a catheter down the jugular vein (in the neck), through theheart, and toward the abdomen. Portograms usually require anesthesiaand are more invasive than scintigraphy or CT scans. They are usuallyquite safe, however, and are able to provide a picture of the PSS so thatthe veterinarian can see where it is located and whether there is morethan one. Many board certified surgeons have an X-ray machine, calleda C-arm, in their operating rooms, which allows them to quickly andsafely perform a portogram during surgery.Computed tomography, known as CT or “CaT” scan, is a techniquethat provides multiple cross-sectional X-rays of bones and organs.CT scans are usually performed under anesthesia. In a dog witha PSS, a CT can be used to make the diagnosis of a shunt and todetermine the specific location of the shunt. This makes surgicalintervention easier, particularly when the shunt is hidden insidethe liver. Preoperative CT scans are often performed on large breeddogs because they usually have intrahepatic shunts.9
“To be certain a dog has PVH-MVD, advanced imaging andliver biopsy are required.”—TobiasLiver BiopsyFigure 3. Photograph of the two small incisions made from alaparoscopic spay and biopsy.Liver biopsy can be obtained by open surgicaltechnique (“laparotomy”) or by laparoscopy (use of ascope). (Figure 3) Ultrasound-guided needle biopsiesare not recommended because small liver size in dogswith congenital PSS and PVH-MVD increases the riskof complications, and because the small sample sizeobtained by needle makes diagnosis of MVD difficult.Some clinicians recommend taking samples frommultiple liver lobes, since the amount of disease coulddiffer from lobe to lobe. (Figure 4)If a Yorkie has no clinical signs,normal urine and biochemistryresults, and mildly increasedpostprandial bile acids, the mostcommon cause is PVH-MVD.—TobiasFigure 4. Micrograph taken of a slide from a liver biopsy specimenrevealing the classical pathology of PVH-MVD.10
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