Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

358 Small Animal Radiolo g y and Ultrasono graphy
D O U B L E -CONTRAST C Y S T O G R A P H Y
In most clinical situations, the double-contrast cystogram is the preferred technique to
study the urinary bladder, because it provides the best evaluation of the mucosal surface.
440 Furthermore, it is the most sensitive test for identifying free intraluminal objects
(e.g., urocystoliths, blood clots). In performing this procedure, the bladder is catheterized,
all urine is removed, and the bladder is distended with a gas such as carbon dioxide,
nitrous oxide, or air. Although the bladder should be fully distended to evaluate the
bladder wall properly, a determination that the bladder is normal can be made without
complete distention, and distention can mask signs of mild to moderate cystitis. 440,441
The volume of gas needed to maximally distend the bladder varies with the individual
and the disease. Bladder palpation is required to judge when adequate distention has
been achieved. After insufflation with gas, a small amount of water-soluble, iodinated
contrast medium (0.5 ml for a cat to 3.0 ml for a large dog) is instilled through the urinary
catheter (remember to allow for the dead space in the catheter). After instillation of
both contrast agents, four views are recommended: a right and left lateral, a ventrodorsal,
and a dorsoventral. If it is practical to take only two views, then one lateral view and
a ventrodorsal view should be performed. However, there is the risk of missing attached
intraluminal objects, such as urocystoliths, polyps, neoplasms, and blood clots, if they are
not in the dependent position and surrounded by the puddle of contrast medium during
the exposure. 442
P O S I T I V E-CONTRAST C Y S T O G R A P H Y
When frank hematuria is present or bladder rupture is suspected, the pneumocystogram
and double-contrast cystogram are contraindicated. This is due to the possibility of a fatal
air embolism (as has been reported following pneumocystograms in patients with hematuria).
443,444 A positive-contrast cystogram (PCC) or EU is recommended. Other considerations
when choosing a special procedure for evaluating suspected bladder rupture
include the difficulty in observing free peritoneal air with hydroperitoneum and the superiority
of the PCC in delineating the point of bladder rupture. To perform a PCC, all urine
should be removed from the bladder and it should be maximally distended with dilute contrast
medium at a concentration of about 80 mg of iodine/ml. Right or left lateral, ventrodorsal,
dorsoventral, and oblique views are recommended as needed, depending on the
differential diagnoses considered.
Normal Cystogram. The normal bladder is ovoid with a tapering neck, which is longer in
the female dog and in the cat than in the male dog. The bladder wall is uniform in diameter.
A contrast puddle should be evident in the center of the dependent portion of the bladder
when a double-contrast cystogram has been performed. Air or contrast may reflux into
the ureters or renal pelvis following bladder distention. 445-448 This is a normal finding.
However, in the presence of cystitis, vesicoureteral reflux may predispose the animal to
pyelonephritis.
R E T R O G R A D E U R E T H R O G R A P H Y
Although not uniformly accepted, retrograde urethrography and real-time ultrasonography
have complementary roles in the assessment of the canine prostate gland. 54,449 We recommend
the combination of distention, positive-contrast cystourethrography, and
ultrasonography be performed in sequence (urethrocystogram followed by ultrasonogram)
to evaluate fully the prostate gland and the associated prostatic and membranous
portions of the urethra, as well as the neck of the urinary bladder.
The retrograde urethrogram performed without bladder distention will evaluate the
urethra for filling defects, leaks, and obstruction, but variances in the intramural aspects of
the urethra may be underestimated. A retrograde urethrogram infrequently may reveal
prostatic pathology, but the study has little value as a routine procedure for the evaluation
of prostatic disease. 450 We do not routinely recommend this procedure for evaluation of
the prostate gland unless paired with ultrasonography. Ultrasonography provides an easier
and more thorough examination of the prostate gland if only one procedure is to be
performed.