Page 1180 - Clinical Small Animal Internal Medicine

1118 Section 10 Renal and Genitourinary Disease

(a) (b)
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Figure 122.9 Ultrasound images of ureteral obstruction in a dog (a) and cat (b). In both images, moderate to severe dilation of the renal
pelvis (*) and proximal ureter (between the +) can be appreciated. The dog suffered from transitional cell carcinoma of the bladder and
the cat from ureterolithiasis.

Bowman’s space, resulting in impairment or even cessa­ Breed predilections are observed in dogs with upper
tion of glomerular filtration. With experimental acute urinary tract calculi, with miniature schnauzers, Lhasa
ureteral obstruction, renal blood flow initially increases, apsos, shih tzus, and Yorkshire terriers affected with
but gradually declines as ureteral hydrostatic pressure greater frequency than other breeds. No consistent
rises and the obstruction is not alleviated. Permanent breed differences have been reported in cats specific to
damage to the kidney occurs within days to weeks after ureterolithiasis. There are breeds of dog that are recog­
ureteral obstruction though if the obstruction can be nized to have a greater incidence of urothelial malig­
alleviated rapidly, there may be no permanent effect on nancy than others. Specifically, the Scottish terrier,
renal function. Experimental studies in dogs suggest the Shetland sheepdog, beagle, wire‐haired fox terrier, and
obstructed kidney will recover only a fraction of its ini­ West Highland white terrier are reported to have an
tial, normal GFR after weeks of complete obstruction increased risk.
even if the obstruction is completely alleviated at that The effect of gender on prevalence of ureterolithiasis is
time. In the setting of bilateral ureteral obstruction, the unclear. It has been suggested that male cats are more
effect on GFR is even more dramatic. This implies that frequently affected by urolithiasis in general than
diagnosis of ureteral obstruction is an urgent problem females, though reports evaluating solely ureteral stones
that requires rapid deobstruction to preserve renal func­ suggest a higher proportion of female cats. In dogs with
tion, particularly as animals with ureteral obstruction ureterolithiasis, there are fewer cases reported, but a
often are older and likely have a degree of renal compro­ female majority was also observed. Female dogs have
mise prior to the development of the obstruction. been recognized as having a higher prevalence of urothe­
lial neoplasia compared to males; additionally, castrated
dogs of both sexes are at higher risk for transitional cell
Epidemiology and Signalment
carcinoma compared to sexually intact dogs.
Large‐scale epidemiologic studies of ureteral obstruction
in veterinary medicine are lacking. As described above, the History and Clinical Signs
cause in most feline cases appears related to ureterolithia­
sis while the cause in dogs is often related to ureterolithiasis The signs of ureteral obstruction are often nonspecific,
or urothelial malignancy. The epidemiology of urolithiasis with vomiting, lethargy, and inappetence commonly
(both upper and lower urinary tract) in small animals sug­ reported. Abnormalities in urination, such as pollaki­
gests that from the 1980s to the early 2000s, there was an uria, hematuria, or stranguria, can also be seen, which
increasing frequency of this condition in both dogs and may be related to concurrent lower urinary tract
cats, concurrent with an increased proportion of calcium uroliths, lower urinary tract infection, or ureteral irri­
oxalate calculi compared to struvite. This trend for increas­ tation. Weight loss may be reported if the animal
ing calcium oxalate calculi in cats appears even more dra­ has a chronic course of disease with compromised
matic when only upper urinary tract stones are considered. renal function. Increased urination and thirst may also
In dogs with ureterolithiasis, struvite and calcium oxalate be observed, associated with renal dysfunction if
calculi seem to be found in a comparable proportion. present.