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26

Normal Urinary System
Judith Hudson

Department of Clinical Sciences, College of Veterinary Medicine, Auburn, AL, USA

26.1 Normal Radiographic Anatomy excretory urography, the latter is preferred for evaluation of
ruptured ureter or ectopic ureter. It can also provide a
Feline kidneys are more moveable than those of the dog. crude estimate of renal function [2,3].
Although the right kidney is usually more cranial than the Excretory urography should not be performed in animals
left, as in the dog, its cranial pole is not buried in the liver, that are dehydrated or in severe renal failure. The abdomen
unlike that of the dog. Consequently, the right kidney is should be prepared prior to the procedure by fasting the
more visible in the cat than in the dog. Unless the cat is very patient and administering an enema if necessary
thin, both kidneys are usually clearly visible when normal (Figure 26.3). Although ionic or nonionic iodinated contrast
although the right kidney is often obscured by overlying media can be used, we prefer the use of nonionic products. A
intestines on the ventrodorsal projection (Figure 26.1). dosage of 600–880 mg/kg of iodine has been recommended
Radiographically, renal size has been compared to measure- for ionic products [3,4] but it may be possible to reduce the
ments of the lumbar vertebrae. Using excretory urography, dosage when nonionic products are used. In a study compar-
investigators found the length of the feline kidney to be ing the use of a nonionic contrast medium (iohexol) to an
2.4–3.0 times and the width 3.0–3.5 times the length of L2 ionic contrast medium (amidotrizoate) for excretory urogra-
on the ventrodorsal projection (Figure 26.2) although in phy in cats [5], iohexol administered at 400 mg of iodine per
cats that are neutered or greater than 10 years old, the kg produced images superior to those acquired with ami-
kidneys may only be 2.0 times the length of L2. The smaller dotrizoate administered at 880 mg of iodine per kg. The dos-
kidney size has not directly been associated with laboratory age should be increased by 10% in cats with increased blood
evidence of renal failure [1]. The feline bladder is more urea nitrogen (BUN) and creatinine levels [3].
cranial than the canine bladder and generally surrounded The sequence of exposures is variable based on individ-
by fat, making it more clearly visualized. ual preference [1,3,4]. An immediate ventrodorsal projec-
tion can be followed by lateral and ventrodorsal projections
at five minutes. Oblique projections at five minutes may
26.2 Contrast Radiography reveal the termination of the ureters into the bladder [1].
Additional lateral and ventrodorsal images can be acquired

26.2.1 Excretory Urography at 20 and 40 minutes. It may be necessary to extend the pro-
cedure in cats with poor renal function to allow opacifica-
Excretory urography should be part of the routine diagnostic tion of the urinary tract [3].
arsenal when ultrasound is unavailable. It is useful when- A belly band can placed across the abdomen to compress
ever there is a need for better visualization of the kidneys, the ureters, resulting in improved visibility of the pyelo-
renal pelvis/diverticula or ureters. It can also help obtain gram [5]. Some practitioners use the belly band only if the
more information about disease of the urinary bladder diverticula are not visible; others use it routinely for the
when catheterization is not possible. When calcification is entire study. Without compression, the diverticula meas-
noted on survey radiography, excretory urography can help ure less than 1–2 mm while the ureters measure less than
localize the calcification to the pelvis, diverticula, or renal 2–3 mm. Size and opacity of the pyelogram will be increased
cortex. Although ultrasonography is generally superior to when compression is applied.

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.