Overview

Occurrence of a urolith (calculus) within the lumen of a ureter (ureterolith); most ureteroliths originate in the renal pelvis and so commonly occur in association with nephroliths. If the uroliths pass through the ureters into the lower urinary tract, a dog or cat may be asymptomatic or may have silent hematuria. If both ureters become totally obstructed in an otherwise healthy untreated dog or cat, death will occur in approximately 4 or 5 days

Signalment

• Dog and cat.
• Breed, age, and sex predispositions vary with type of nephrolith.

Signs

• May be initially asymptomatic.
• Pain (ureteral colic) during passage of ureteroliths or following acute ureteral obstruction.
• Renomegaly if ureteral obstruction leads to hydronephrosis.
• “Big kidney, little kidney syndrome” is being recognized with increasing frequency in cats in which obstruction of one ureter has previously occurred, resulting in a shrunken end-stage kidney; signs of renal failure and hydronephrosis occur due to obstruction of the remaining functional kidney.
• Unilateral ureteral obstruction results in azotemia and uremic clinical signs only when the function of the contralateral kidney is compromised.
• Signs referable to a lower urinary tract infection or septicemia may be present concurrently with ureterolithiasis.
• Ureteral rupture may occur, resulting in urine accumulation in the retroperitoneal space.
• Cats with distal ureteral obstruction may have signs of dysuria and pollakiuria.

Causes & Risk Factors

• For a list of causes, see chapters on each urolith type.
• Most ureteroliths in dogs and cats are composed of calcium oxalate. Dogs may form struvite nephroliths and subsequent ureteroliths from infection with urease-producing bacteria. Cats may have ureteroliths composed of dried solidified blood clots.
• Circumcaval ureters (more commonly in right ureter) appear to predispose cats to obstruction of the ureter by ureteroliths and secondary ureteral stricture formation.
• Prior treatment of nephroliths by extracorporeal shock wave lithotripsy, medical dissolution, or surgery to remove nephroliths may be additional risk factors.

Differential Diagnosis

• Consider in all cases of renal failure unilateral or bilateral renomegaly, abdominal pain, or fluid accumulation in the retroperitoneal space. Obstruction to urine outflow to both kidneys will not produce the same magnitude of renomegaly as unilateral obstruction because the patient will perish as a result of bilateral disease before the changes in the kidneys occur.
• Radiopacities detected by survey abdominal radiography that may be confused with ureteroliths include particulate fecal material in the colon, mammary gland nipples, peritoneoliths, calcified lymph nodes, and mineralization of the renal pelvis.
• Radiolucent ureteroliths may be difficult to differentiate from ureteral blood clots. Other causes of ureteral obstruction include intraluminal tumors, ureteroceles, ureteral strictures (secondary to ureteroliths, circumcaval ureter, prior surgery or trauma), and extraluminal compression. Hydroureter and hydronephrosis may occur because of ureteral ectopia, pyelonephritis, and obstruction of the ureteral opening at the trigone (most commonly due to transitional cell carcinoma of the bladder).

CBC/Biochemistry/Urinalysis

These tests evaluate renal function and screen for concurrent disease before the ionized treatment of ureterolithiasis. Urinalysis, serum calcium concentration, and fractional excretion of electrolytes may permit estimation of urolith composition pending results of definitive analysis.

Other Laboratory Tests

• Submit all retrieved ureteroliths for quantitative analysis to determine appropriate preventive strategies.
• Patients (other than Dalmatians and bulldogs) with urate stones should be evaluated for portosystemic shunts.
• Blood pressure should be monitored since hypertension is common with CKD secondary to ureteral obstruction.

Imaging

• Radiography-radiopaque ureteroliths may be visualized. If obstruction and hydronephrosis have occurred, renomegaly may be apparent. If ureteral rupture occurs, contrast in the retroperitoneal space may be lost. Small uroliths may not be visualized on radiographs even if they are radiopaque.
• Contrast radiography-when ureteroliths are suspected, but cannot be documented, an intravenous urogram may help to identify the site of obstruction and will also distinguish ureteral rupture from retroperitoneal hemorrhage. In many instances the damaged tubules do not concentrate contrast media adequately, resulting in poor delineation of the ureter. Intraoperative nephropyelocentesis is performed during surgical placement of SUB or ureteral stents in cats, allowing for confirmation as part of the surgical correction.
• Ultrasonography-valuable for detecting hydronephrosis or hydroureter. Changes suggesting pyelonephritis may also be detected by ultrasound. The dilated proximal ureter may be traced to the ureterolith and thus allow ultrasonographic confirmation. Ureteroliths are not observed ultrasonographically in approximately 25% of cats with ureteroliths.
• Computed tomography before and after IV contrast can be used to confirm obstructive ureteroliths if they are suspected but not confirmed by other imaging modalities.

Diagnostic Procedures

• Nuclear scintigraphy alone should not used to determine whether or not to preserve or surgically remove a kidney.
• Voiding urohydropropulsion may be performed to retrieve ureteroliths that have spontaneously passed into the bladder.

Pathologic Findings

Gross changes in the kidney-progressive dilation of the pelvis and calyces; in advanced cases, the kidney may be transformed into a thin-walled sac with only a thin shell of atrophic cortical parenchyma; ureteral dilation proximal to the site of obstruction is typical.

Drug(s)

• Medical dissolution is largely ineffective for ureteroliths.
• Therapy aimed at prevention of recurrent disease is imperative following relief of obstruction.
• For ureteroliths that are not causing severe obstruction or severe renal functional problems, allowing time for the ureterolith to spontaneously pass down the ureter to the bladder may eliminate the need for ureteral surgery.

Contraindications/Possible Interactions

Attempts to prevent one type of urolith may promote formation of a second type.

Patient Monitoring

• Following SUB placement, sampling the SUB for urinalysis and culture along with flushing the SUB under ultrasonographic monitoring is recommended every 3 months.
• Following successful removal of ureteroliths, recheck every 3–6 months for recurrence of uroliths and to ensure owner compliance with preventive measures; urinalysis, radiographs (or ultrasound), and a urine culture are usually appropriate.

Prevention/Avoidance

• Elimination of factors predisposing to the development of urolithiasis.
• Specific therapy depends on the mineral composition of the urolith.

Possible Complications

Hydronephrosis, CKD, recurrent urinary tract infection, pyelonephritis, sepsis, ureteral rupture, ureteral stricture, hypertension.

Expected Course and Prognosis

Highly variable; if unilateral disease is present, the opposite kidney retains adequate function, and recurrence is prevented, the prognosis is good. Prognosis is good for cats with SUB or ureteral stent placement that recover renal function to stage 1–2 CKD.

Abbreviations

• CKD = chronic kidney disease
• ESWL = extracorporeal shock wave lithotripsy
• SUB = subcutaneous ureteral bypass