Page 704 - Clinical Small Animal Internal Medicine

672 Section 7 Diseases of the Liver, Gallbladder, and Bile Ducts

Historically, mesenteric portovenography was widely of the caudal vena cava (between the hepatic veins and
VetBooks.ir used for the definitive confirmation of a suspected porto- right atrium), for example by thrombosis, neoplasia or
inflammation. Ultrasound findings include hepatomegaly,
systemic shunt and for the differentiation between intra
and extrahepatic shunts. The most popular technique for
portovenography is the intravenous injection of non- reduced hepatic echogenicity, dilation of the hepatic veins
and caudal vena cava and, in some cases, the presence of
ionic iodinated contrast media through a catheter pre- free abdominal (+/− pleural) fluid. Radiographs may show
placed into a mesenteric vein. This involves a laparotomy hepatomegaly and loss of serosal detail in patients with
and is an invasive procedure. Alternative and potentially ascites, possibly with evidence of a pleural effusion and
less invasive, but less commonly used, techniques for cardiomegaly in patients with right‐sided heart failure.
contrast administration include percutaneous ultra-
sound-guided catheterization of the splenic vein, cathe- Portal Hypertension
terization of the cranial mesenteric artery via the femoral Chronic portal hypertension resulting in the develop-
artery and transvenous retrograde portography. In many ment of portosystemic collaterals (acquired portosys-
cases, mesenteric portovenography has been superseded temic shunts) is relatively common in dogs, but rarely
by contrast Computed Tomographic examination. identified in cats. Causes of portal hypertension include
However, during surgical occlusion of a shunt, portove- advanced chronic liver disease (cirrhosis), intrahepatic
nography is still used to verify that the correct vessel has arterioportal fistulae, congenital hypoplasia of the portal
been occluded, to check that there are no additional vein and portal vein obstruction. Ultrasound evaluation
shunting vessels and to assess the degree of portal vascu- of patients with portal hypertension will typically dem-
larization post-ligation. Fluoroscopic imaging of the con- onstrate ascites, often with edema of the gallbladder wall
trast injection provides useful real time information (Fig and pancreas. Spectral Doppler is useful in measuring
61.18): if this is not available, then standard radiographic portal velocity; the identification of reduced flow veloc-
views (ideally both lateral and VD views, each exposed at ity (from a normal velocity of approximately 17+/-
the end of a separate contrast injection) should be taken. 5cm/s to <10 cm/s in the dog), and occasionally reversed
portal flow, is very suggestive of portal hypertension.
Hepatic Congestion The portosystemic collaterals open in response to sus-
Disturbance of the normal venous outflow results in pas- tained portal hypertension and connect the portal sys-
sive hepatic congestion. Causes include right‐sided heart tem directly to the systemic circulation. These acquired
failure and obstruction or compression of the cranial part shunting vessels can be challenging to identify on ultra-

Figure 61.18 Ventrodorsal intraoperative fluoroscopic image acquired immediately after the administration of nonionic contrast medium
into a mesenteric vein. The contrast highlights a left gastro-azygos extrahepatic portosystemic shunt (blue arrow). Source: Rob White,
School of Veterinary Medicine and Science, University of Nottingham