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appropriate care may contribute to an irreversible decrease in kidney function.20 Problematic nephroliths should be removed by (1) dissolution, (2) endoscopic nephrolithotomy (ie, for nephroliths too large for extracorporeal shock wave lithotripsy and for nephroliths in cats), and (3) extracorporeal shockwave lithotripsy
(for nephroliths in dogs only). Extracorporeal shockwave lithotripsy has minimal effects on renal function, but is reserved for nephroliths ≤1.5 cm in diameter. Nephroliths >1–1.5 cm often require concurrent ureteral stent placement. A diagnosis of a ureteral obstruction should be based on ultrasonographic  ndings of hydronephrosis and associated hydroureter proximal to an obstructive ureterolith regardless of the degree of the renal pelvic dilatation. If renal pelvic dilatation is <5 mm, careful imaging is needed to con rm obstruction unless it is associated with concurrent hydroureter proximal to
an obstructive urolith. If no obstructive lesion is seen
on ultrasound examination, abdominal radiography should be performed concurrently to evaluate for the presence of nephroureteroliths. If ureteroliths are not visualized, a ureteral obstruction is not necessarily excluded, because ureteral strictures are common (>25% of cats). In a study evaluating the causes of hydronephrosis, all renal pelves >13 mm were associated with ureteral obstruction and those >7 mm were
likely associated with ureteral obstruction. Partial and complete ureteral obstructions should be managed as
an emergency regardless of whether the obstruction
is partial or complete. Interventional procedures, such
as ureteral stents and subcutaneous ureteral bypass, have a lower morbidity and mortality rate for ureteral obstruction than do traditional surgical options in both dogs and cats, respectively.21} Medical management
of stable obstructive ureterolithiasis can be considered for 24– 72 hours. Medical treatment should include
 uid diuresis and mannitol continuous rate infusion treatment, if tolerated. Alpha adrenergic antagonists
and tricyclic antidepressants also have been used
with anecdotal reports of improvement in some cases. Medical treatment should not be continued in animals that are persistently oliguric or anuric, hyperkalemic,
have progressive azotemia and progressive renal
pelvic dilatation; minimally invasive urolith extraction or bypass is needed. Fluid treatment should be closely monitored to prevent overhydration. In dogs, in addition to propulsive treatment for uroliths, broad-spectrum antimicrobials IV (ideally for at least 24 hours before intervention) should be administered. Ureterolith-induced ureteral obstructions should be monitored rather than decompressed when renal pelvic dilatation is ≤3–5 mm, and renal function is stable. Medical management for
the treatment of cats with ureteral obstructions is only reported to be effective in 8–13% of cases.20 Because over 25% of ureteral obstructions in cats are associated with concurrent ureteral strictures, success of medical management often is limited. Subcutaneous ureteral
An Urban Experience
bypass or ureteral stenting for ureteral obstructions in cats should be considered the  rst choice for the best possible outcome. Interventional options such as ureteral stent placement, extracorporeal shockwave lithotripsy,
or both for the treatment of ureteral obstructions in dogs always should be considered and offered to clients. Ureteral stents are associated with the lowest short- and long-term morbidity and mortality rates when compared to all other reported treatment options. Careful assessment of urinalysis (eg, crystals, urine
pH), urine culture results, radiographic appearance,
and when possible, quantitative urolith analysis should always be performed. In dogs, suspected struvite ureteroliths should be stented and then dissolved. Suspected obstructed calcium oxalate ureteroliths should be either stented for long-term treatment or stented with concurrent or subsequent extracorporeal shockwave lithotripsy, if necessary. Cystine and urate ureteroliths should be treated by a ureteral stent and concurrent medical and dietary treatment. Ureteral stents in dogs often can be placed endoscopically. Owners should be aware of reobstruction risks that are most often associated with concurrent ureteral stricture. Knowing the urolith composition will help by employing appropriate medical and dietary treatment to prevent stent encrustation and future urolith formation. If stenting fails, other options such as extracorporeal shock wave lithotripsy and subcutaneous ureteral bypass device placement, or traditional surgery, can be considered. Dogs with ureteral obstruction should have their urine cultured and should be given antimicrobial treatment at the time of diagnosis because of the high incidence of concurrent UTI and pyonephrosis.
Removal or bypass of uroliths will not alter the underlying conditions responsible for their formation. The most effective prevention strategies are those that eliminate the underlying cause. For cases in which a cause remains elusive or cannot be altered, minimize pathophysiologic risk factors associated with formation. Nutritional treatment remains a subject of much clinical interest and debate because of epidemiological and pathophysiological data associating nutrient intake
with urine saturation and lithogenicity. For all mineral types (except infection-induced struvite), feeding
diets high in moisture is one of the cornerstones of urolith prevention strategies. Primary treatment for preventing infection-induced struvite uroliths, which
is the most common struvite urolith in dogs, is early identi cation and elimination of UTI. Eliminating these infections will prevent recurrence of infection-induced struvite uroliths. Foods marketed to treat struvite urolithiasis will not prevent their recurrence but may delay or minimize, urolith burden in the presence of unrecognized UTI. Calcium oxalate urolithiasis in dogs and cats appears to be driven primarily by hypercalciuria

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