Initial diagnostic plans
In your opinion, are further diagnostic procedures indicated at this time?
Since the lower urinary tract disease is recurrent, the answer is yes. Our experience is that palpation is an insensitive
and unreliable method to detect uroliths.
What about detecting uroliths by radiography? Survey abdominal radiography will reveal radiodense uroliths in approximately
one in 10 patients with lower urinary tract disease. Double-contrast cystography will detect uroliths in approximately 25
percent of affected cats. Therefore, in order to rule in (inclusion diagnosis) or rule out (exclusion diagnosis) uroliths,
survey and contrast radiographic evaluation of the urinary tract was recommended.
Figure 1: A survey abdominal radiograph of a 3-year-old castrated cat illustrating a radiodense urocystolith (arrow).
Survey radiographs of the abdomen revealed one large urocystolith (Figure 1). Retrograde positive contrast urethrocystography
revealed a urachal diverticulum at the vertex of the urinary bladder (Figure 2). A broad-spectrum antimicrobial was given
orally for seven days to minimize the possibility of a urinary catheter-induced urinary tract infection (UTI).
Figure 2: A positive contrast urethrocystogram of the cat described in Figure 1 illustrating a vesicourachal diverticulum.
On the basis of available data, can you predict the mineral composition of the urocystolith? Would you choose ammonium urate,
calcium oxalate, calcium phosphate, cystine, magnesium ammonium phosphate, silica or some other type of mineral? What is the
basis for your choice?
Our "guesstimate" of the mineral composition of the urocystolith was sterile magnesium ammonium phosphate because:
1. Bacteria were not identified by urine culture.
2. The urocystolith was large, radiodense and had a smooth surface contour.
3. Magnesium ammonium phosphate crystals were observed in the urine sediment.
4. Ammonium urate, calcium oxalate, calcium phosphate and cystine crystals were not observed in the urine sediment.
5. The urolith was located in the urinary bladder (nephroliths are more likely to contain calcium salts).
6. The urine pH was only slightly acidic.