Objective—To test the hypothesis that feline calcium
oxalate uroliths are intrinsically more resistant to comminution
via shock wave lithotripsy (SWL) than canine
calcium oxalate uroliths through comparison of the
fragility of canine and feline uroliths in a quantitative
in vitro test system.
Sample Population—Calcium oxalate uroliths (previously
obtained from dogs and cats) were matched by
size and mineral composition to create 7 pairs of
uroliths (1 canine and 1 feline urolith/pair).
Procedure—Uroliths were treated in vitro with 100
shock waves (20 kV; 1 Hz) by use of an electrohydraulic
lithotripter. Urolith fragmentation was quantitatively
assessed via determination of the percentage
increase in projected area (calculated from the digital
image area of each urolith before and after SWL).
Results—After SWL, canine uroliths (n = 7) fragmented
to produce a mean ± SD increase in image area of 238
± 104%, whereas feline uroliths (7) underwent significantly
less fragmentation (mean image area increase of
78 ± 97%). The post-SWL increase in fragment image
area in 4 of 7 feline uroliths was < 50%, whereas it was
> 150% in 6 of 7 canine uroliths.
Conclusions and Clinical Relevance—Results indicate
that feline calcium oxalate uroliths are less susceptible
to fragmentation via SWL than canine calcium oxalate
uroliths. In some cats, SWL may not be efficacious for
fragmentation of calcium oxalate nephroliths or
ureteroliths because the high numbers of shock waves
required to adequately fragment the uroliths may cause
renal injury. (Am J Vet Res 2005;66:1651–1654)