Page 740 - Small Animal Internal Medicine, 6th Edition

712 PART V Urinary Tract Disorders

CHAPTER 43
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Canine and Feline

Urolithiasis

INTRODUCTION PRINCIPLES OF STONE ANALYSIS
Stones can be analyzed by a variety of methods. Calculi
Urolithiasis is a common urinary tract disorder of dogs and submitted to the Gerald V. Ling Urinary Stone Analysis
cats. Clinical signs of urolithiasis are variable, depending on Laboratory at the University of California at Davis (http://
the location of the urolith. Pollakiuria, stranguria, dysuria, www.vetmed.ucdavis.edu/usal/index.cfm) are analyzed by
and hematuria may be noted by owners and suggest a quantitative crystallographic analysis primarily with the oil
problem in the lower urinary tract of their cat or dog. Clini- immersion method of optical crystallography using polar-
cal signs in cats and dogs with upper urinary tract uroliths ized light microscopy. In addition to optical crystallography,
are variable and can include hematuria or clinical signs com- infrared spectroscopy (IR) is routinely used to process all
patible with acute kidney injury secondary to ureteral calculus specimens suspected of containing uric acid crystals
obstruction; ureterolithiasis may also be an incidental and/or salts of uric acid crystals to determine the presence
finding. of xanthine, hypoxanthine, allopurinol, or oxypurinol, a
The most common uroliths in dogs and cats, calcium metabolite of allopurinol, which may be present in the speci-
oxalate (CaOx) and struvite, are radiodense and can usually mens. Polarized light microscopy alone is insufficient to
easily be identified on plain radiography. Cystine and urate identify these metabolites. Other advanced analytic tech-
uroliths are less radiodense, and contrast cystourethrograms niques (e.g., microprobe analysis, X-ray diffractometry) are
or ultrasonography are often required to identify these available for certain stones if the mineral composition is not
stones. Although ultrasonography is a sensitive diagnostic well identified with optical crystallography or IR. The author
for bladder and proximal urethral uroliths (Fig. 43.1), it is recommends that stones removed from animals be submit-
not a good imaging modality for visualizing the entire ted to a veterinary stone analysis laboratory in order to help
urethra of male dogs and cats, and urethroliths could be properly tailor the best management strategies and track
missed if abdominal radiography is not performed. It is research trends.
important to position the animal’s legs properly to obtain
diagnostic images of the lower urinary tract (Fig. 43.2). STONE REMOVAL
Although ultrasonography does limit exposure to radiation, A consensus statement regarding the most common uroliths
the size of the stone may be more accurately predicted by in small animals has been recently published (Lulich et al.,
radiography. Furthermore, radioopacity can be determined. 2016), and the reader is referred to that statement for addi-
This information is clinically relevant when developing sur- tional details regarding upper and lower urinary tract uroli-
gical and minimally invasive strategies for urolith removal. thiasis and minimally invasive stone removal techniques.
Urolithiasis as well as other lower urinary tract disor- The panel agreed that minimally invasive stone removal
ders (e.g., neoplasia, granulomatous urethritis, urethral should be discussed with all clients if clinically appropriate
foreign body, obstructive feline idiopathic cystitis [FIC], and available in one’s area. These include laparoscopic-
functional urethral outflow tract obstruction) can result assisted cystostomy, percutaneous cystolithotomy, voiding
in urethral obstruction. Obstruction with urethroliths is urohydropropulsion (VUH) (Video 43.1), basket retrieval of
more common in male dogs because of their longer, nar- a stone via the cystoscope (Fig. 43.3; Video 43.2), and
rower urethra. Uroliths will often obstruct the area of the holmium:YAG laser lithotripsy (Fig. 43.4; Video 43.3). Some
pelvic urethra or become lodged at the base of the os penis. uroliths such as struvite, urate, and cystine may be amenable
Managing a urethral obstruction is described in Chapter to medical dissolution. Although protocols for dissolution of
44; the principles described in that section are similar struvite uroliths in cats and dogs can be successful, protocols
for dogs. for dissolution of suspected urate and cystine stones are

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