Page 595 - Atlas of Small Animal CT and MRI

Urinary Tract 585

a result of necrotic tissue, tumor tissue, and hemorrhage. Trauma
Renal dysplasia may also result in cyst formation, and
affected kidneys are usually small, differentiating them Abdominal trauma can result in injury to renal paren-
from polycystic kidney disease. 10 chyma or vasculature. Although reports in the literature
are lacking, expected abnormalities could include renal
Ectopic ureters or perirenal hematoma, renal capsule tear, and renal
Abnormal termination of one or both ureters distal to vasculature avulsion (Figure 5.8.8). CT is the imaging
the trigone of the bladder results in urinary inconti- modality of choice in people although MR is used when
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nence and hydroureter in female dogs. Ectopic ureters iodinated contrast medium is contraindicated or CT is
are uncommon in male dogs and in cats. Multiple unavailable.
modalities are used to diagnose ectopic ureters, includ- Traumatic imaging characteristics can be extrapo-
ing CT, cystoscopy, ultrasonography, excretory lated from findings in people. Intrarenal hematomas
urography, and vaginourethrography. CT is among the result in hypoattenuating foci in the renal cortex on
most sensitive methods to detect ectopic ureters and contrast‐enhanced images. Subcapsular hematoma
has the advantage of evaluating the kidneys, ureters, appears as a hypoattenuating collection conforming
and urethral termination, without interference from to the outer renal capsule, highlighted by the contrast‐
the pelvis, and providing functional information enhanced renal parenchyma. When laceration of the
(Figure 5.8.5). The ureters fill with contrast approxi- kidney also occurs, hemorrhage can extend to the
12
mately 2 minutes following intravenous contrast retroperitoneal space. Deep lacerations or avulsion
administration and are normally segmentally opacified can result in disruption or disconnection of the col-
as a result of peristalsis. Furosemide injection can lecting system and renal vasculature. Contrast may
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improve the number of ureteral segments visualized extravasate, and renal parenchymal enhancement is
18
and the diameter of the segments during the pyelo- poor.
gram phase. 14 Lower urinary tract disruption results in leakage of
The stream of contrast entering the bladder trigone urine into the retroperitoneal and/or peritoneal space.
is hyperattenuating to urine and can demarcate the Expected imaging signs include extravasation of con-
vesiculoureteral junction. Ureters terminating in the trast medium from the ureter or bladder, similar to
caudal trigone or urethra travel close to midline and excretory urography or cystography. CT can eliminate
intramurally or occasionally extramurally. Ureteroceles superimposition of structures and is expected to have
can occur as dilations of the terminal ureter in dogs greater sensitivity to small volumes of contrast leakage
with ureteral ectopia, causing a thin‐walled structure compared to radiographs. In our experience, images
partially obstructing the ureter at the junction with acquired with the patient in both dorsal and ventral
the trigone (Figure 5.8.6). Secondary abnormalities recumbency are sometimes required to detect the region
include ipsilateral hydroureter and hydronephrosis of bladder rupture.
resulting from chronic obstruction or pyelonephritis. Vascular disorders
In hydronephrotic kidneys, decreased renal function
can be inferred from delayed pelvic and ureteral opaci- Renal infarcts are recognized as wedge‐shaped areas of
19
fication although dilution of contrast may occur from decreased attenuation in the renal cortex. Acute
urine stasis. infarcts may be subtle regions of hypoattenuation,
progressing to larger regions as time progresses
Retrocaval ureter (Figure 5.8.9). The renal vasculature has three to four
Retrocaval ureter, also termed circumcaval ureter, results large interlobar arteries centrally and smaller interlob-
from a developmental anomaly of the caudal vena cava ular arteries peripherally, obstruction of which may
and ureter. The prevalence in cats is approximately 35% cause segmental or smaller peripheral infarcts, respec-
and is normally right sided, although left or bilateral tively (Figure 5.8.10). In chronic infarcts, the renal
circumcaval ureter may be present. The anomaly is contour may be depressed because of tissue atrophy
sometimes associated with double caudal vena cava. and fibrous replacement. These are frequently seen in
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Fewer reports are available in dogs, with left retrocaval animals with and without clinical signs of renal dys-
ureter and transposition of the caudal vena cava reported function. On MR images, acute infarcts are expected to
(Figure 5.8.7). Contrast‐enhanced MR urography was be T1 and T2 hypointense, changing to T1 and T2
deemed a good diagnostic technique. Ureters may cir- hyperintense from 1 day to 1 week post infarction, and
16
cumnavigate the caudal vena cava and have been associ- T1 and T2 hypointense after 2 weeks as fibrosis replaces
ated with strictures in cats. 17 normal tissue. 20

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