CONTRAST MEDIUM-RELATED ARTIFACTS OBSERVED DURING IN VITRORADIOGRAPHIC CHARACTERIZATION OF UROCYSTOLITH MINERAL COMPOSITION

Nine pure mineral types of canine uroliths (bladder or urethral origin only) were exposed to sequential increasing concentrations of iodinated, radiographic contrast medium in petri dishes. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (Brushite), ammonium acid urate, sodium acid urate, cystine, and silica. Two phenomena were observed. First, there was a tendency for selected urocystoliths to undergo radiopacity augmentation beyond that expected for just contrast medium superimposition. This was termed, contrast medium adhesion, which persisted despite repeated washing of the urocystoliths. Second, there was a tendency for bubbles to form on or near selected urocystolith chemical types. These observations prompted careful scrutiny for their occurrence in subsequent clinical simulation of radiographic procedures using these same urocystoliths in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations). The contrast medium adhesion occurrence found in the petri dish studies was compared to urocystolith mineral type. Similar comparisons were made for contrast medium adhesion occurrence in the bladder phantom. The detection of contrast medium adhesion in the bladder phantom differed from that observed in the petri dish experiments. While contrast adhesion occurred across a fairly broad range of the urocystolith mineral types in the petri dish studies, it was observed primarily for sodium acid urate and cystine urocystoliths in the bladder phantom. Prompted by the observation of bubbles in association with a limited number of urocystolith types in the petri dish studies, bubble occurrence in the bladder phantom was compared to the urocystolith type. Bubble formation on or near the urocystoliths, although uncommonly observed, was seen only with either cystine or silica urocystoliths. The potential clinical utility and clinical caveat aspects of these phenomena are discussed.     

Prevalence of canine uroliths. Minnesota Urolith Center

Uroliths obtained from 839 dogs were evaluated by quantitative methods. Struvite was the most prevalent mineral detected; newberyite, calcium oxalate, calcium phosphate, uric acid, sodium and ammonium urate, cystine, and silica were detected much less frequently. Seven per cent of the uroliths had an identifiable nucleus and one or more surrounding layers of different mineral types. Although uroliths were found in all parts of the urinary tract, the urinary bladder was most common. Uroliths of different composition were encountered in a variety of breeds of both sexes and different ages.     

Relationship of nutritional factors to the cause, dissolution, and prevention of feline uroliths and urethral plugs

Feline lower urinary tract disease is often associated with uroliths and urethral plugs. Uroliths and urethral plugs are composed of variable quantities of matrix and a variety of minerals (including struvite, calcium oxalate, ammonium urate, calcium phosphate, and cystine). Knowledge of nutritional factors associated with the pathophysiology of uroliths and urethral plugs facilitates the modification of diets for the dissolution of several minerals contained within them.     

RELEVANCE OF SONOGRAPHIC ARTIFACTS OBSERVED DURING IN VITRO CHARACTERIZATION OF UROCYSTOLITH MINERAL COMPOSITION

Nine pure mineral type canine uroliths (bladder or urethral origin only) were imaged ultrasonographically using 3.5 MHz, 5.0 MHz, and 7.5 MHz fixed focus, mechanical sector transducers in a urinary bladder phantom. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The occurrence of both reverberation/streak and acoustic shadowing artifacts were compared to urocystolith mineral type (classified by effective atomic number), urocystolith width, urocystolith height (thickness), and ultrasonographic imaging frequency. No predictable relationship was found between either of the artifacts seen beyond the urocystolith (reverberation/streak or the acoustic shadowing) and urocystolith mineral type. There was no statistical relationship between the occurrence of reverberation/streak artifact and the size (width or height) of the urocystolith or the ultrasonographic frequency. There was, however, a statistically relevant relationship between ultrasonographic imaging frequency and the occurrence of acoustic shadowing and between urocystolith height (thickness) and the occurrence of acoustic shadowing. However, regardless of ultrasound frequency, acoustic shadowing was observed less than 35% of the time in any of the urocystolith mineral types examined. Based on the imaging of the bladder phantom supporting apparatus (7.0 mm bolts covered by plastic), the accurate characterization of a curved object surface directly facing the transducer was found to be directly related to the frequency of sound used for imaging and at best predictably limited to curved vs flat. Accurate measurement of the maximum transverse dimension of an echogenic curved object or accurate characterization of the lateral borders of such an object was considered unlikely with general ultrasonographic equipment of the frequencies studied. Therefore, detailed architectural characterization of urocystoliths suitable for mineral composition prediction is considered highly unlikely with general pulse-echo ultrasonographic techniques.     

Study of cystine urinary calculi in dogs.

The composition and structure of 48 canine cystine urinary stones were determined by infrared spectroscopy, scanning electron microscopy and electron dispersive X-ray analysis. The infrared analysis showed that about 45% of the specimens were composed of pure cystine. The remainder also contained calcium oxalate (mono and/or dihydrate), magnesium ammonium phosphate hexadydrate (struvite), calcium hydrogen phosphate dihydrate (brushite) and complex urates (ammonium, ammonium potassium and/or potassium enriched ammonium urate). The infrared study of several samples heated at 620 degrees C and 750 degrees C revealed the presence of apatitic calcium phosphate. This compound was difficult to detect in the spectrum of the original samples due to the small proportion of phosphate contained in the calculi and to band overlapping. The examination of a series of selected samples by means of scanning electron microscopy and energy dispersive X-ray analysis complemented the infrared results.     

Qualitative and quantitative analysis of uroliths in dogs: definitive determination of chemical type

Effective treatment and prevention of urolithiasis depends on accurate determination of the chemical nature of the uroliths. A widely used qualitative chemical procedure was compared with quantitative crystallographic analysis of 272 canine uroliths. Agreement between the 2 methods was 78%. Qualitative analysis failed to detect 62% of calcium-containing uroliths and 83% of carbonate apatite uroliths. Qualitative analysis gave false-positive results for urates in 55% of cystine uroliths. Mixed uroliths comprising 6% of the total could not be classified without quantitative analysis. Silicate, cystine, and urate uroliths generally were of pure composition. Crystallographic analysis indicated the following distribution of major types: struvite, 69%; calcium oxalate, 10%; urate, 7%; silicate, 3.5%; cystine, 3.2%; calcium phosphate, 1%; and mixed, 6%. Among dogs with struvite uroliths, 66% had positive results of bacterial culturing from the urinary bladder. Six breeds (Miniature Schnauzer, Welsh Corgi, Lhasa Apso, Yorkshire Terrier, Pekingese, and Pug) had a significantly higher risk for urolithiasis, compared with other breeds. The German Shepherd Dog had a significantly lowered risk, compared with other breeds. Two breeds had significant relationship to a specific type of urolith: Miniature Schnauzer for oxalate, and Dalmatian for urate (P less than 0.001). It was concluded that quantitative analysis, using crystallography, was superior for the detection of calcium oxalate, carbonate apatite, cystine, urate, and mixed uroliths.     

Comparison of three techniques for the diagnosis of urinary tract infections in dogs with urolithiasis

OBJECTIVES: To identify an appropriate sampling technique(s) to accurately detect the bacteria causing urinary tract infections in dogs with urolithiasis. METHODS: Twenty-one dogs with urolithiasis were included in the study. Three types of samples were taken from each dog. Urine was collected by cystocentesis, and a urinary bladder mucosal biopsy and urolith were retrieved during cystotomy. The samples were then cultured on blood agar and MacConkey's agar to identify the bacteria associated with urinary tract infections. RESULTS: Bacterial urinary tract infection was found in 16 cases (76.19 per cent). The most prevalent bacteria found to cause urinary tract infection were Escherichia coli (n=7), followed by coagulase-positive Staphylococcus species (n=4), Klebsiella pneumoniae (n=2), Pseudomonas aeruginosa (n=2) and Proteus mirabilis (n=1). In the case of a positive urine culture, the same bacteria were also cultured from the urinary bladder mucosal biopsy alone or from both the urinary bladder mucosal biopsy and urolith. However, in the case of a negative urine culture, bacteria were found to be present in the urinary bladder mucosal biopsy or urolith cultures in 23.81 per cent of dogs. The uroliths that gave positive culture results were either infection-induced uroliths composed of struvite and calcium carbonate phosphate, ammonium acid urate only or metabolic uroliths composed of calcium oxalate and calcium phosphate, or calcium phosphate only. All the uroliths that gave negative culture results were metabolic uroliths composed of calcium oxalate and/or calcium phosphate, and uric acid and calcium phosphate. CLINICAL SIGNIFICANCE: When the culture from the urine obtained by cystocentesis is negative, cultures of urinary bladder mucosal biopsy and urolith are recommended in dogs with urolithiasis in order to accurately assess the microbiological status of the urinary tract.     

Feline matrix-crystalline urethral plugs: A unifying hypothesis of causes

The hypothesis is advanced that various combinations of aetiologically different events may lead to three different, but common, clinical manifestations of feline lower urinary tract disease. One manifestation, characterised by nonobstructive haematuria, dysuria, pollakiuria, and increased production of proteinaceous and cellular inflammatory reactions occurs as a consequence of urinary tract infections with viruses and occasionally other infectious agents. A second manifestation is that of classical urolithiasis, which occurs in response to oversaturation of urine with different types of calculogenic substances. Naturally occurring feline uroliths containing magnesium ammonium phosphate, calcium oxalate, ammonium urate, calcium phosphate, cystine and xanthine have been observed. A third manifestation, resulting from the concomitant occurrence of urinary tract infections and various types of urine crystals, is characterised by formation of matrix-crystalline plugs that may obstruct the urethra, especially of male cats. Preliminary data suggest that urethral plug matrix contains Tamm-Horsfall mucoprotein, similar to that observed involved in the formation of renal tubular casts.     

Medical dissolution of feline struvite urocystoliths

The efficacy of a diet designed to facilitate dissolution of feline magnesium ammonium phosphate (struvite) uroliths was evaluated in 30 cases of urolithiasis, sterile struvite uroliths dissolved in a mean of 36 days after initiation of dietary treatment. In 5 cases of urolithiasis, struvite urocystoliths associated with urease-negative bacterial urinary tract infection dissolved in a mean of 23 days after initiation of dietary and antimicrobial treatment. In 3 cases of urolithiasis, struvite urocystoliths associated with urease-positive staphylococcal urinary tract infection dissolved in a mean of 79 days after initiation of dietary and antimicrobial treatment. Dissolution of uroliths in cats fed the treatment diet was associated with concomitant remission of dysuria, hematuria, and pyuria, and reduction in urine pH and struvite crystalluria. In one case, a urocystolith composed of 100% ammonium urate, and in another case, a urolith composed of 60% calcium phosphate, 20% calcium oxalate, and 20% magnesium ammonium phosphate did not dissolve.     

Surgical removal of canine uroliths

Surgery is indicated for patients with obstructive uropathy; calcium oxalate, calcium phosphate, silica, and perhaps cystine uroliths; uroliths refractory to medical dissolution; nephrolithiasis and progressive renal dysfunction; anatomic defects predisposing to urinary tract infection; and problems precluding medical management. The goals of surgical management include removal of all uroliths while preserving organ function, eliminating partial or complete obstruction to urine outflow, and correction of anatomic abnormalities that predispose the patient to infection and or urolithiasis.     

Pure cystine and urate calculi can be clearly visible using survey digital radiography

Cystine and urate calculi are considered nonradiopaque to faintly radiopaque. Two canine cases in which these types of calculi are radiopaque and clearly apparent in vivo on survey digital radiography are described. The densities of cystine and urate calculi, as determined in vitro with computed tomography, are compared to other pure calculi and mixed or compound calculi to further explore the relative attenuation characteristics.     

Structure and composition of canine urinary calculi

The chemical constituents of 171 specimens of canine urinary calculi have been analysed by infrared spectroscopy. The analysis revealed that 46 per cent of the total contained struvite as the major component; 26 per cent contained cystine; 16 per cent were found to be composed of whewellite and, or, weddellite; 8 per cent of urates; 3 per cent of calcium phosphate (apatite and, or, brushite) and 1 per cent of silica. A series of selected samples was also studied by scanning electron microscopy and energy dispersive X-ray analysis (EDAX). This examination revealed structures similar to human stones. Potassium and complex urates containing two or more cations were commonly found in many areas of ammonium urate and sodium urate calculi. Moreover, EDAX analysis detected a calcium enriched urate in several zones of urate calculi.     

In vitro evaluation of canine and feline calcium oxalate urolith fragility via shock wave lithotripsy

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.     

In vitro prediction of canine urolith mineral composition using computed tomographic mean beam attenuation measurements

Determination of urolith mineral composition is critical for management of urolithiasis in dogs and cats. Using computed tomography, urolith physical density, and hence chemical composition, can be quantified using mean beam attenuation measurements (Hounsfield units; HU). This study was designed to establish in vitro reference ranges for three types of compositionally pure uroliths retrieved from dogs. Sixty-six canine uroliths (22 uric acid, 21 calcium oxalate, 14 struvite, nine mixed or compound) were placed in a phantom array. Uroliths were scanned at 120 kVp, 200 mA, and 80 kVp, 200 mA. The region of interest (ROI) for mean HU calculation was determined using two techniques, and reference ranges were calculated for each kVp using either ROI technique. HU for urolith types of pure composition were statistically different (Wilcoxon's two-sample test, P < 0.0083 [Bonferonni correction with six comparisons for total P < 0.05]) using both ROI techniques at either kVp. Struvite uroliths were not statistically different from mixed or compound uroliths. The accuracy for determination of composition of pure uroliths ranged from 86% to 93%; the prediction accuracy for each urolith mineral type and for all uroliths in general was highest when the ROI was hand-drawn just within the visible urolith border at 80 kVp. Technique of ROI determination and kVp that yielded the highest sensitivity, specificity, and positive and negative predictive values varied for each urolith type. Therefore, in this study, HU could be used to differentiate three types of uroliths of pure mineral composition in vitro. Further studies are needed to determine the predictive value of HU in vivo.     

The distribution of canine urinary calculi and their recurrence following treatment

The composition of urinary calculi was determined in 110 cases of canine urolithiasis and it was found that phosphate was the main constituent in 44% of cases, oxalate in 32%, cytsine in 22% and urate in 2%. Magnesium ammonium phosphate calculi were frequently found in female dogs while in male animals calculi composed of calcium salts or cystine were common. The mean age of dogs with calculi composed of magnesium ammonium phosphate was 6 years while for calcium calculi the mean age was 8-6 years and for cystine calculi 4–9 years. Recurrence of urolithiasis was studied in sixty dogs and further calculi were found in thirty-two animals when examined radiographically although only nineteen of these showed clinical signs. Recurrent calculi developed in 75% of cases where the calculi were composed of calcium or cystine but in only 30% of cases with magnesium ammonium phosphate. The recurrent stones usually had a similar composition to the initial calculi. Résumé. On a précisé la composition de calculs urinaires dans 110 cas d'urolithiase canine et or trouvé que le phosphate était le principal constituant dans 44% des cas, l'oxalate dans 32%, cystine dans 22% et l'urate dans 2%. On a fréquemment trouvé des calculs de phosphates d'amrr nium magnésium chez les chiens femelles tandis que chez les animaux mâles les calculs composés sel de calcium ou de cystine étaient communs. La moyenne des âges des chiens avec des calculs coi posés de phosphate d'ammonium magnésium était de 6 ans, alors que pour les calculs de calcium moyenne des âges était de 8,6 ans et pour les calculs de cystine de 4,9 ans. On a étudié une recurren d'urolithiase chez soixante chiens et on a trouvé d'autres calculs chez trente-deux chiens quand i les a examinés à la radiographie bien que dix-neuf seulement aient montré des signes cliniqui Des calculs récurrents se sont développés dans 75% des cas oà les calculs se composaient de cystine i de calcium mais dans seulement 30% des cas avec du phosphate d'ammonium magnésium. L pierres recurrentes avaient généralement une composition semblable à celle des calculs initiaux. Zusammenfassung. Die Komposition von Harnsteinen wurde in 110 Fällen von Hunde-Har steinen bestimmt und man fand, dass Phosphat der Hauptbestandteil in 44% aller Fälle war, Oxal in 32%, Cystin in 22% und Urat in 2%. Magnesiumammoniumphosphatsteine wurden häufig weiblichen Hunden gefunden, während in männlichen Tieren Steine die aus Kalziumsalzen od Cystine zusammengesetzt waren, gewöhnlicher waren. Das Durchschnittsalter von Hunden ir Harnsteinen die aus Magnesiumammoniumphosphat bestanden belief sich um 6 Jahre während fi Kalziumharnsteine das Durchschnittsalter 8,6 Jahre war und für Gystinharnsteine 4,9 Jahre. Ma studierte das Wiederauftreten von Harnsteinen in sechzig Hunden und weitere Harnsteine fande sich in zweiunddreissig Tieren, als sie radiographisch untersucht wurden, obwohl nur neunzehn vo diesen klinische Symptôme zeigten. Emeute Harnsteine entwickelten sich in 75% aller Fälle in dene die Harnsteine aus Cystine oder Kalzium zusammengesetzt waren aber in nur 30% von Fällen m Magnesiumammoniumphosphat. Die erneut auftretenden Steine waren gewöhnlich von ähnlichi Komposition wie die anfänglichen Harnsteine.     

Association between dietary factors and calcium oxalate and magnesium ammonium phosphate urolithiasis in cats.

OBJECTIVE: To identify dietary factors associated with the increase in occurrence of calcium oxalate (CaOx) uroliths and the decrease in occurrence of magnesium ammonium phosphate (MAP) uroliths in cats. DESIGN: Case-control study. ANIMALS: 173 cats with CaOx uroliths, 290 cats with MAP uroliths, and 827 cats without any urinary tract diseases. PROCEDURE: Univariate and multivariate logistic regression were performed. RESULTS: Cats fed diets low in sodium or potassium or formulated to maximize urine acidity had an increased risk of developing CaOx uroliths but a decreased risk of developing MAP uroliths. Additionally, compared with the lowest contents, diets with the highest moisture or protein contents and with moderate magnesium, phosphorus, or calcium contents were associated with decreased risk of CaOx urolith formation. In contrast, diets with moderate fat or carbohydrate contents were associated with increased risk of CaOx urolith formation. Diets with the highest magnesium, phosphorus, calcium, chloride, or fiber contents and moderate protein content were associated with increased risk of MAP urolith formation. On the other hand, diets with the highest fat content were associated with decreased risk of MAP urolith formation. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that diets formulated to contain higher protein, sodium, potassium, moisture, calcium, phosphorus, and magnesium contents and with decreased urine acidifying potential may minimize formation of CaOx uroliths in cats. Diets formulated to contain higher fat content and lower protein and potassium contents and with increased urine acidifying potential may minimize formation of MAP uroliths.     

Prevalence and chemical composition of uroliths in fattening pigs in Belgium

The present study investigated the prevalence of uroliths in fattening pigs and assessed the composition of these urinary tract concrements. In total, 2,432 urinary bladders were sampled in the slaughterhouse and checked for abnormal content. Urinary samples were analysed microscopically, and samples of the urinary bladder wall were tested for histological signs of inflammation. The composition of the concrements was examined by infrared spectrophotometry. Macroscopic and microscopic abnormalities were detected in 8.4% and 52.8% of the samples respectively. Magnesium ammonium phosphate (struvite), calcium oxalate dihydrate (COD), calcium carbonate (calcite), calcium oxalate monohydrate (COM) and amorphous crystals were detected. Analysis of stones showed COD in all samples in different proportions. The calcium content of examined stones was always considerable (up to 34%), in contrast to the magnesium content which represented max 1.9%. Struvite was found in one third of the samples, but was never part of stones and grit. COD crystals were the second most common microscopic crystal. These COD crystals and some COD stones had a rectangular shape, and therefore, they can be harmful to the bladder mucosa. In conclusion, uroliths are present in a large proportion of male fattening pigs, and consequently, urinary concrements pose a life‐threatening risk for urethra obstruction in male pigs. Further research is warranted to identify potential risk factors for urolithiasis and microscopic crystals.     

Laser lithotripsy for treatment of canine uroliths

OBJECTIVE: To confirm in vivo optimal laser energy settings previously determined in vitro for lithotripsy, to develop a technique for Ho:YAG laser lithotripsy, and to evaluate acute and chronic tissue effects of laser lithotripsy. STUDY DESIGN: Prospective, randomized preclinical trial. ANIMALS OR SAMPLE POPULATION: Nineteen intact, adult male dogs. METHODS: Via cystotomy, a single urolith was inserted into the urethra to the level of the base of the os penis to simulate obstruction. Uroliths (calcium oxalate, urate, or magnesium ammonium phosphate) were fragmented by Ho:YAG laser, in contact mode through a 320 micro optic fiber, passed through the operating channel of a 2.8 mm flexible endoscope. The time and total energy to fragmentation were recorded. Dogs were euthanatized immediately after lithotripsy (3 dogs) or at 3 days (7 dogs), and urethral lesions and any stone remnants were evaluated. Urethral integrity was also evaluated in 9 other dogs by endoscopy on day 10; these were also monitored clinically for 30 days. RESULTS: The mean time for adequate fragmentation was 166.7 seconds (range, 47-494.5 seconds). The mean+/-SD energy used was 1418+/-851.2 J. In part 1, 2 dogs were obstructed with urolith fragments at necropsy. Eight dogs had minimal (<30 mg) or no urolith material evident within the urethra. Four dogs had gross focal or circumferential erosion, ulceration, or hemorrhage of the urethral mucosa. Lesions were not associated with the site of laser irradiation in 2 dogs. In dogs observed for 30 days, hematuria, pollakiuria, and stranguria that were observed after lithotripsy, resolved in all affected dogs by day 5. No mucosal lesions were observed by endoscopy and none of the dogs became obstructed. CONCLUSION: Laser lithotripsy with the Ho:YAG laser in contact mode successfully fragmented obstructive uroliths in male dogs. CLINICAL RELEVANCE: Laser lithotripsy may be a clinically relevant technique for treatment of urolithiasis in male dogs; clinical studies to evaluate long-term effects on urethral mucosa and the role of repeat treatment for recurrence are indicated.     

Cystinuria in the dog: clinical studies during 14 years of medical treatment

The purpose of this study was to summarize 14 years of clinical experience with medical treatment of 88 cystinuric dogs. Of special interest was evaluation of recurrence rate of cystine uroliths and adverse effects during long-term tiopronin treatment. Twenty-six different breeds were recognized, and the most common breeds were Dachshunds, Tibetan Spaniels, and Basset Hounds. In 76 of 88 treated dogs (86%), re-formation of cystine uroliths was prevented. Recurrence rate of cystine uroliths changed from 7 months before to 18 months during tiopronin treatment. On 28 occasions, bladder stones were found, and in about 60% of the dogs, the uroliths dissolved. Quantitative measurement of the urinary excretion of cystine showed a significantly (P < .03) higher excretion of cystine in dogs with recurrent urolith formation than in dogs with only 1 urolith episode. Another finding was a significant (P = .02) decrease in urinary cystine excretion in older (>5 years) than in younger (<5 years) dogs. Adverse effects were found in 11 dogs, and the most severe signs were aggressiveness and myopathy. All signs disappeared when tiopronin treatment was stopped. In conclusion, this study emphasizes the importance of an individual strategy for lifelong treatment of cystinuria. In addition to increasing water intake, chemical modification of the cysteine molecule into a more soluble form by means of tiopronin is useful. In dogs with re-formed cystine uroliths, dissolution may be induced by increasing the tiopronin dosage to 40 mg/kg body weight per day. In dogs with a low urolith recurrence rate and low urinary cystine excretion, the tiopronin dosage may be decreased or treatment discontinued.     

UROCYSTOLITH DETECTION: COMPARISON OF SURVEY, CONTRAST RADIOGRAPHIC AND ULTRASONOGRAPHIC TECHNIQUES IN AN IN VITRO BLADDER PHANTOM

Urocystoliths of 9 mineral types from 437 canine patients submitted to the University of Minnesota Urolith Bank were imaged in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations) and real-time ultrasonography (3.5 MHz, 5.0 MHz, 7.5 MHz). Imaging techniques were compared for accuracy of urocystolith detection, accuracy of urocystolith enumeration, and tendencies for over or undercounting. Across urocystolith mineral types, the false negative rates (no urocystoliths detected in a given case) for survey radiographs range from 2 to 27%. Pneumocystographic techniques are one-half as likely to yield false negative results as are survey radiographic techniques. Underestimates of urocystolith numbers and false negatives are likely using 80 mg iodine/ml double contrast cystography because calcium-based urocystoliths are isopaque in this contrast medium dilution. The 200 mg iodine/ml double contrast cystographic techniques are unlikely to yield false negative diagnoses even for very small (< or = 1.0 mm) urocystoliths and is comparable to pneumocystography for detection and slightly better for enumeration. The likelihood of an ultrasonographic false negative for urocystoliths decreases with increasing MHz. Under optimal conditions using a 7.5 MHz mechanical sector transducer, the false negative rates were comparable to double contrast cystography, but rates increased notably with lower MHz transducers.