Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 277
injection, to ensure that the contrast is injected into the spleen and not into the peritoneal
cavity, are the major difficulties in this procedure. Another method of demonstrating these
structures is the operative mesenteric portogram. In this procedure, a laparotomy is performed
and a mesenteric vein is cannulated with an 18-gauge intravenous catheter.
Iodinated water-soluble contrast medium (200 to 400 mg iodine per ml) is injected manually
at a dosage of 1 ml/kg of body weight, and radiographs are taken as the last part of
the injection is delivered. This technique requires either intraoperative radiographs or multiple
closures and repeated openings of the abdominal incision. The third method uses the
venous phase of an injection of contrast into the cranial mesenteric artery. 71 Because fluoroscopy
is required and the detail of the venous phase is sometimes poor, this method is
performed infrequently. Of the three techniques, operative mesenteric portography currently
is the technique used most frequently. Transcolonic portography using a radioisotope
has become popular as a screening procedure for the detection of portosystemic
shunts. This technique requires the use of a scintillation (gamma) camera and usually is
available only at referral centers.
G A L L B L A D D E R
Cholecystography. Cholecystography is performed to visualize the gallbladder. 72-74 This
may be done for a questionable location of the gallbladder (e.g., suspected diaphragmatic
hernia) or if obstruction to bile flow is suspected. 75,76 The applicability of this procedure
in biliary obstruction is quite limited, because the liver handles the contrast medium in the
same manner that it handles bilirubin. Therefore in icteric animals it is quite unlikely the
gallbladder will opacify in an adequate manner, because the liver will regurgitate both bile
and contrast medium and prevent accumulation of the contrast within the gallbladder.
Both oral and intravenous contrast agents have been used in dogs and cats. Oral cholecystography
has been performed in dogs using calcium iodopate at a dosage of 150 mg/kg
body weight. In cats, oral cholecystography has been performed using iobenzamic acid at
a dosage of 50 mg/kg and iodopate at a dosage of 150 mg/kg. Radiographs are obtained 12
to 14 hours following contrast administration. Intravenous cholecystography has been performed
in dogs using iodipamide at a dosage of 0.5 mg/kg and in cats at a dosage of 1
ml/kg, as well as with meglumine iotroxate at a dosage of 72 mg/kg. 77 Although the contrast
may be seen in the gallbladder as early as 15 minutes postinjection, radiographs usually
are obtained 60 minutes after intravenous injection.
Percutaneous transhepatic cholecystography has been performed safely in dogs. 78 A needle
is placed in the liver under fluoroscopic guidance and radiopaque water-soluble contrast is
injected as the needle is withdrawn. The gallbladder is identified by flow of contrast into the
lumen. The gallbladder is monitored as it is filled with contrast material, and filling is continued
until the contrast flows into the common bile duct and reaches the duodenum. Aspiration
of the contrast and bile is performed before the needle is removed from the gallbladder.
Twenty to thirty ml of contrast usually is required for average-size dogs (11 to 25 kg). A similar
technique can be used for cholangiography, in which the contrast is identified within an
intrahepatic bile duct or hepatic vein as the needle is withdrawn using fluoroscopy. These techniques
are of limited value and are available only at centers that have fluoroscopic equipment.
An alternative to fluoroscopy is ultrasonographically guided cholecystography and is used
when it is specifically indicated to assess the gallbladder and extrahepatic biliary ducts. 79
Although the gallbladder and bile ducts can be evaluated using ultrasonography, limited
functional information can be obtained. Sincalide, a synthetic cholecystokinin, has been
used to induce gallbladder emptying in order to obtain some functional information and
distinguish between obstructive and nonobstructive biliary disease. The drug is injected
intravenously at a dosage of 0.04 µg/kg, and the response of the gallbladder is monitored
using ultrasonography. Normal dogs and dogs with nonobstructive biliary disease reduce
the volume of the gallbladder by 40% within 1 hour, while obstructed dogs reduced their
gallbladder volume less than 20%. Side effects to the injection were not reported. 80
G A S T R O I N T E S T I N A L S Y S T E M
Gastrointestinal Series. Noncontrast radiographs should always precede a GI contrast
study. This approach may save you the effort, the patient the discomfort, and the owner