Page 594 - Atlas of Small Animal CT and MRI

5.8

Urinary tract

Introduction quantify renal volume with good accuracy. Contrast‐
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enhanced MR urography gives excellent information on
The urinary tract is frequently evaluated with CT renal anatomy and function, but it is less commonly
because of its excellent spatial resolution for examining used.
small structures, such as ureters or small calculi. The Contrast‐induced nephropathy (CIN) has been
function of each kidney can also be subjectively evaluated described in people, which results in acute kidney injury,
by evaluation of the renal and urine enhancement with causing an increase of creatinine of more than 0.5 mg/dl
contrast medium. Quantitative functional analysis has or 25% over baseline within 48 hours of contrast
also been investigated using dynamic CT and perfusion administration. This has not been fully characterized in
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techniques. 1,2 dogs and cats; however, similar risk factors and preven-
The kidneys, ureters, bladder, and urethra can be tion measures can be extrapolated. Hypovolemia, exist-
imaged with CT and MR (Figures 5.8.1, 5.8.2). Renal ing renal dysfunction, nephrotoxic drugs, hypotension,
contrast enhancement is multiphasic as contrast medium heart failure, and diabetes are risk factors for
is filtered by the urinary system (Figure 5.8.3). The cortex CIN. The use of iso‐ and low‐osmolar contrast medium
enhances to a greater degree than the medulla on the decreases risk of CIN, as does pre‐ and postcontrast
initial corticomedullary phase. The nephrogram phase hydration with intravenous saline. 7
shows uniform renal enhancement prior to urine
collecting in the renal pelvis. The renal pelvis and medulla Developmental disorders
are enhanced during the excretory phase. The ureters fill
segmentally with contrast medium as a result of peristal- Renal cysts
tic contractions during the excretory phase. The ureters Autosomal dominant polycystic kidney disease results
enter the dorsal bladder wall near the trigone. The urethra in progressive development and enlargement of
is less commonly evaluated with cross‐sectional imaging low‐attenuation cysts in the renal cortex in cats. The
but is easily included by scanning through the pelvis, and disease has also been reported in dogs. In adult animals,
CT urethrography can be performed to better delineate the origin of cysts, whether congenital or degenerative,
the urethral lumen. may be undetermined. Cysts may deform the capsule
CT angiography is used to evaluate the anatomy of and distort the renal pelvis and are best seen on contrast‐
the renal vasculature, which is advantageous for surgical enhanced images (Figure 5.8.4). Solid tumors and/or
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planning. There is normally one artery and one vein replacement of renal tissue with cystic structures occurs
3,4
supplying each kidney; however, anatomic variants of in hereditary multifocal renal cystadenocarcinomas in
additional arteries and veins occur frequently in cats. German Shepherd Dogs, along with nodular
4
MR angiography of the canine renal vasculature has also dermatofibrosis and uterine neoplasia. These cysts
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been described. CT software applications can be used to often have attenuation greater than 5 HU, presumably as
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Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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