Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

400 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-189 A 7-month-old female
domestic short-haired cat with
stranguria and pollakiuria for 3
weeks. Survey radiographs reveal
multiple poorly calcified calculi
(white arrows) in the urinary bladder.
Diagnosis: Multiple cystic calculi.
multitude of shapes. Oxalate calculi do not commonly assume any particular shape, but
they often have a rough surface and are usually in the 3- to 8-mm diameter range. For their
size, they are more dense than struvite and often are equal to or greater than the ilial wing
opacity. There is a predominance of oxalate urocystoliths in middle-aged to older male
dogs. Cats usually have smaller uroliths and the oxalate mineral types are more common
in males, as well as neutered and older cats. 681 Struvite stones are more common in
younger and female cats. Multiple small calculi, also known as cystic sand, may be seen in
dogs or cats and can be clinically significant (Fig. 3-190). A radiograph obtained using a
horizontal x-ray beam with the patient standing may be useful in identifying small opaque
calculi or sand, because this material will form layers in the urinary bladder, thereby
increasing their opacity. If not contaminated with calcium salts, two types of calculi, uric
acid and cystine calculi, are usually radiolucent and not apparent on the survey film. Uric
acid stones, if visible at all, will be poorly calcified, relatively small, and frequently have an
oblong appearance. Struvite calculi that are composed predominately of ammonium or
magnesium phosphate may be nearly radiolucent. If radiolucent calculi are suspected, a
double-contrast cystogram or ultrasonographic examination is indicated.
Dystrophic mineralization of the bladder mucosa may occur secondary to bladder
inflammation or tumor. In chronic severe cystitis, such as that seen secondary to administration
of cyclophosphamide, the bladder wall may appear as an eggshell-type of calcification
affecting only the mucosa (Fig. 3-191). In neoplasms, there may be focal areas of
dystrophic mineralization that usually appear as stippled or small foci of calcification in a
limited portion of the bladder (Fig. 3-192). Focal areas of bladder mineralization may be
differentiated from calculi because of their position. Calculi will tend to remain in the
dependent portion of the urinary bladder and will move with changes in the patient’s position.
Mural and polypoid mineralization will be fixed in position and will be constant
despite changes in the patient’s position. 433 Differentiating small ureteral calculi, which are
in the ureter at the trigone, from mineralization of the bladder wall can be difficult.
Gas densities may be seen occasionally in the bladder. The most common cause is the
introduction of a small amount of air when the bladder is catheterized. This produces a
small gas-dense bubble in the center of the bladder (Fig. 3-193). Emphysematous cystitis
may occur in animals (1) that have diabetes mellitus and a bladder infection caused by a
glucose-fermenting organism such as Escherichia coli or (2) with chronic cystitis, when the
mucosa become hypoxic and infection with a gas-forming organism such as Clostridium
occurs (Fig. 3-194). 433,682-685 The gas density will be seen in the submucosa and appears as