Abstract
Case Description—2 dogs and 5 cats were evaluated for treatment of ureteroliths.
Clinical Findings—Spontaneous retrograde movement of 1 or more ureteroliths was detected by radiography, ultrasonography, fluoroscopy, and a combination of fluoroscopy and ultrasonography. The ureteroliths moved retrograde up to 4 centimeters. Retrograde movement of ureteroliths into the renal pelvis resulted in improved renal function in some patients but made complete surgical removal of all uroliths more difficult.
Treatment and Outcome—Medical management was not successful, and ureteroliths were surgically removed. Surgical management of ureteroliths was complicated by retrograde movement of ureteroliths in the perioperative period.
Clinical Relevance—Ureteroliths can move retrograde within the ureter and even back into the renal pelvis. Retrograde movement of ureteroliths may make surgical planning more difficult.
A4-year-old neutered male domestic shorthair weighing 3.0 kg (6.6 lb) was admitted to the hospital for apparent dysphagia. The cat was quiet, alert, and responsive and had a body condition score of 1/5. Heart rate was 200 beats/min, rectal temperature was 37.7°C (100.5°F), and respiratory rate was 24 breaths/min. A CBC and serum biochemical analyses revealed Hct of 26.3% (reference range, 30% to 45%), total plasma protein concentration of 8.2 g/dL (reference range, 6.0 to 8.0 g/dL), BUN concentration of 94 mg/dL (reference range, 15 to 35 mg/dL), creatinine concentration of 6.1 mg/dL (reference range, 0.9 to 2.3 mg/dL), phosphorus concentration of 9.6 mg/dL (reference range, 2.6 to 8.8 mg/dL), and globulin concentration of 4.2 g/dL (reference range, 2.3 to 3.8 g/dL). Urinalysis revealed urine specific gravity of 1.012 with 0 to 2 WBCs/hpf, 10 to 14 RBCs/hpf, and 5 to 9 epithelial cells/hpf. Aerobic bacteriologic culture of urine did not yield bacterial growth.
The cat was administered lactated Ringer's solution (100 mL/kg [45.5 mL/lb]/d, IV) and famotidine (0.5 mg/kg [0.23 mg/lb], IV, q 24 h). Abdominal radiography revealed multiple ureteroliths in the right ureter ventral to the fifth lumbar vertebra. The right renal pelvis contained 2 moderate-sized nephroliths and 1 small nephrolith (Figure 1). Severe bilateral hydronephrosis and right hydroureter were found via ultrasonography. Contrast medium (barium) was administered PO, and radiography did not reveal any abnormalities related to the apparent dysphagia. Excretory urography confirmed the diagnoses of right hydroureter, hydronephrosis, and ureteroliths and revealed that the left kidney did not contain concentrated contrast medium, which suggested that it was nonfunctional. It was noted that spontaneous movement of ureteroliths had occurred between the time of the survey lateral projection and the first radiograph made as part of the excretory urogram 3 hours and 45 minutes later. Serum BUN and creatinine concentrations decreased to 47 and 2.3 mg/dL, respectively, by day 5.
Lateral radiographic views of a cat with ureteroliths. A—Radiographic view obtained early during excretory urography. B—Radiographic view obtained 3 hours and 45 minutes after radiograph A. Uroliths considered to be the same on each image are indicated with double-headed arrows; notice that their position is different between the 2 images and that the cluster of obstructing uroliths is larger in part B. The shape of the uroliths is different between images because they have rotated, providing a different silhouette.
Citation: Journal of the American Veterinary Medical Association 229, 7; 10.2460/javma.229.7.1118
Surgery to remove the left kidney, right ureteroliths, and right nephroliths was scheduled 5 days after initial abdominal radiographs were obtained. Preoperative radiography revealed 3 moderate-sized nephroliths in the right renal pelvis, as opposed to 2 moderate-sized and 1 small nephroliths detected 5 days earlier (Figures 1 and 2). In the region of the obstruction of the ureter, there were fewer ureteroliths. This indicated that 1 of the ureteroliths had moved retrograde approximately 4 centimeters into the right renal pelvis. Additionally, sandlike material had moved retrograde. The left kidney was removed, and 6 ureteroliths were removed from the right ureter via ureterotomy in the proximal dilated portion of the ureter. A 3.5-F urinary catheter was inserted proximally into the renal pelvis, and some of the nephroliths were flushed out through the ureterotomy incision. Despite attempts to locate and remove all of the uroliths, some uroliths remained after surgery. Postoperative radiography revealed 1 urolith in the right renal pelvis, 1 in the distal right ureter approximately at the level of L6, and 1 in the proximal portion of the right ureter. Radiography was repeated 2 days later. One urolith was found in the renal pelvis, and both of the ureteroliths were present in the distal ureter at the level of L6. The BUN and creatinine concentrations were 44 and 2.6 mg/dL, respectively. A second surgery to remove the remaining uroliths was scheduled in 1 month.
Lateral radiographic view of the cat in Figure 1 obtained 5 days later. Notice 3 moderate-sized uroliths in the renal pelvis (arrow cluster) and that the small nephrolith seen in Figure 1 is no longer visible. Fewer uroliths obstruct the ureter (arrowheads). Sandlike material is in the ureter proximal to the obstructing collection of ureteroliths (black arrows).
Citation: Journal of the American Veterinary Medical Association 229, 7; 10.2460/javma.229.7.1118
One month later, preoperative radiography revealed 2 uroliths in the right renal pelvis and 1 ureterolith in the distal portion of the right ureter at the level of L6. One of the ureteroliths had moved retrograde approximately 4 centimeters into the right renal pelvis (Figure 3). Surgery was performed the same day. At the time of surgery, the distal ureterolith was also suspected to have moved retrograde into the right renal pelvis, such that 3 uroliths were present in the right renal pelvis. This suspicion was based on the fact that the distal ureterolith in the right ureter was palpated in the distal portion of the ureter during the initial stages of surgery, and vascular ties were placed around the ureter to attempt to maintain its position; however, when the surgeon was ready to remove the ureterolith, the ureterolith was no longer identifiable in that location. After an extensive attempt to relocate the ureterolith, the surgeon decided that it had likely moved proximally into the right renal pelvis. A proximal ureterotomy was performed to remove the uroliths in the right renal pelvis. Two uroliths were successfully removed from the right renal pelvis, but a third urolith could not be identified. Postoperative radiography revealed that the urolith was again in the distal portion of the ureter. Given the size of the urolith, the surgeon was convinced that it had moved into the renal pelvis during surgery, then back into the ureter after surgery; however, it was not possible to definitively document that movement without intraoperative imaging. The cat recovered from surgery without complications and was discharged with a serum BUN con centration of 33 mg/dL and a creatinine concentration of 2.3 mg/dL.
Lateral radiographic views of the cat in Figure 1. A—View obtained 2 days after surgery for removal of uroliths. B—View obtained 1 month after surgery. Notice that 1 ureterolith has migrated proximally. Double-headed arrows indicate the location of each urolith at the 2 postoperative times.
Citation: Journal of the American Veterinary Medical Association 229, 7; 10.2460/javma.229.7.1118
The cat was reevaluated 24 months after surgery because serum creatinine concentration had increased from a range of 2.1 to 2.2 mg/dL since surgery to 2.4 mg/dL and the BUN concentration was 38 mg/dL. The cat was clinically normal. Abdominal radiography and ultrasonography revealed that there was a right ureterolith in a similar location to the postoperative location 2 years prior. The right kidney was small and had dilatation of the pelvis and proximal portion of the ureter. Ureterotomy was performed, and the ureterolith was successfully removed. Postoperative radiography confirmed urolith removal. The cat was discharged 4 days after surgery with a BUN concentration of 30 mg/dL and a creatinine concentration of 2.1 mg/dL.
During the period from 1992 to 2002, retrograde movement of ureteroliths was detected in our hospital in 4 additional cats and 2 dogs by use of serial abdominal radiography (n = 4), ultrasonography (1), fluoroscopy (1), or a combination of ultrasonography and fluoroscopy (1). The ureteroliths ranged in diameter from 1 to 6 millimeters. Two cats and 1 dog had 2 ureteroliths that moved retrograde, and 1 dog and 3 cats had only 1 ureterolith that moved retrograde. The distance that the ureteroliths moved retrograde was approximately 2 centimeters in both dogs and 4 cats. In 1 cat, 2 ureteroliths moved retrograde, with the most distal ureterolith moving approximately 4 centimeters back into the renal pelvis. In 2 dogs and 1 cat, the uroliths were initially detected in the renal pelvis, subsequently passed into the ureter, and then moved retrograde into the renal pelvis. In both dogs and 1 cat, there was a marked increase of serum creatinine concentrations while the urolith was in the ureter and the serum creatinine concentration decreased when the urolith moved retrograde into the renal pelvis.
Discussion
The 7 cases of this report were obtained from medical records of 115 dogs and cats with nephroliths and ureteroliths seen at Purdue University Veterinary Teaching Hospital from 1992 to 2002. Results of a recent study1 indicate that uroliths of the upper portion of the urinary tract have increased in frequency over the last 20 years, with 2% to 4% of uroliths in cats in the kidney or ureter. Although ureteroliths constitute 4% of the total number of uroliths submitted to stone analysis centers, the actual prevalence may be higher than what is reported.1,2 This may be because of the difficulty of surgically removing ureteroliths, compared with urocystoliths. Alternatively, if owners choose less invasive methods of removal of nephroliths such as extracorporeal SWL, increased prevalence of ureteroliths could result.2–4 The fragments created by SWL ordinarily pass down the ureter into the urinary bladder and are voided.3,4 However, 1 potential complication of this procedure is the production of stone fragments that are small enough to enter the ureter but subsequently become lodged in the ureter.3,4
Deciding how to treat dogs and cats with ureteroliths can be difficult. Presently available options include surgical intervention, SWL, or conservative management.2,3,5–7 Ureteroscopy with laser lithotripsy is often used to remove ureteroliths in humans.8 In human medicine, criteria for intervention include urolith size, urolith location, duration of signs, presence of renal colic, results of blood analyses, evidence of renal damage, and evidence of ureteral obstruction.8–10 Because dogs are likely to be of substantially different sizes, compared with other species, specific criteria for when intervention is required are more difficult to define.
In dogs and cats, conservative medical management by serial monitoring of ureteroliths along with administration of diuretics and IV administration of fluids has been recommended, provided there is minimal renal function compromise and no infection, renal colic, or progressive ureteral dilation.2,4–6,11 Typically, dogs and cats with evidence of complete obstruction, worsening azotemia, or evidence of pyelonephritis should be treated by either surgical intervention or SWL.3,4,6,7,12 In 1 recent report,6 52 cats were treated by medical management alone and serial radiographs were monitored in 14 of these cats. The ureterolith passed spontaneously to the urinary bladder in 9 of these 14 cats.However, 17 of the 52 medically managed cats did not respond to medical management and were euthanatized or died within 1 month.6 The optimal time to allow for passage of ureteroliths by medical management prior to surgical intervention is not known.6,11,13 In 1 retrospective study,6 the interval from initial diagnosis to surgery decreased from 19 days in the initial 11 cats to only 2 days for cats in the later part of the study.
Retrograde ureterolith movement should also be considered when deciding on the management of a dog or cat with ureteroliths. The exact mechanism of retrograde movement of ureteroliths is unknown. Because the ureterolith is moving in the antegrade direction, it can lodge in the ureter and cause the ureter proximal to the ureterolith to dilate. The dilated portion of the ureter, along with changes in body position, allows 1 or more ureteroliths to move under the influence of gravity. Gravity may cause the ureterolith to move in the retrograde direction and potentially into the renal pelvis when the cranial portion of the body is lower than the caudal portion (eg, the animal jumps down from furniture or other elevated surfaces).
We hypothesize that some apparently inactive nephroliths may move into the proximal portion of the ureter intermittently and then move retrograde spontaneously, which may contribute to progressive renal injury. This is most likely to occur when the nephroliths are small enough to readily enter the proximal portion of the ureter but too large to pass through the length of the ureter. This ball-valve effect may be a mechanism whereby nephroliths cause renal failure without ever causing obvious hydroureter and hydronephrosis. In some cats with acute uremia and uroliths of the upper portion of the tract, 1 kidney is enlarged from acute obstruction and hydronephrosis and the contralateral kidney is small and atrophied.6,13 Many of these small kidneys contain nephroliths. The mechanism by which these kidneys become small rather than developing end-stage hydronephrosis is not known. One possible explanation is intermittent obstruction by the nephrolith or ureterolith followed by retrograde movement of the obstructive urolith, allowing for resolution of the hydronephrosis. Multiple intermittent obstructions could result in cumulative renal damage and fibrosis.
The potential for spontaneous retrograde movement makes management of dogs and cats with nephroliths and ureteroliths more difficult. If conservative management is used, the patient should have periodic radiography, ultrasonography, excretory urograms, serum biochemical analyses, and urinalyses.6 Serial monitoring of the serum creatinine concentrations may detect impairment of renal function caused by ureteral obstruction; however, unilateral obstruction will not affect serum creatinine concentration if the contralateral kidney and ureter are healthy. Radiographs should be monitored for antegrade or retrograde movement of the ureterolith or change in the number or size of ureteroliths.2,11,13 The sonogram should be examined for evidence of current or previous ureteral obstructions, such as renal pelvic or ureteral dilatation.13 If an obstruction was present but subsequently resolved, renal pelvic dilation should diminish on serial ultrasound examinations. If the ureterolith is highly mobile, interventional techniques should be considered because the possibility of renal parenchymal damage as a result of repeated intermittent ureteral obstructions exists. Urinalysis should be performed to check for evidence of urinary tract infection. The presence of recurrent urinary tract infections often indicates that there is pyelonephritis secondary to infection of the urolith. With pyelonephritis, more invasive techniques are needed to prevent renal damage.2,6,14
In humans, 90% of ureteroliths will pass within 3 months, 54% will pass within 16 days, and up to 98% of ureteroliths < 5 mm in diameter will pass.8,10 If a ureterolith remains in the same location for 2 weeks in a human, interventional techniques should be considered.8,10 This information can probably be extrapolated for use in veterinary patients with ureteroliths. If a patient is monitored for 2 weeks and the ureterolith is not moving distally, intervention should be considered. In 1 study15 of research dogs with complete ureteral obstruction, relief of the ureteral obstruction within 4 days resulted in essentially complete recovery of glomerular filtration rate, whereas correction of the ureteral obstruction after 14 days resulted in return of only approximately half of normal glomerular filtration rate. Therefore, ureteroliths causing complete ureteral obstruction should be treated within a few days of diagnosis rather than allowing prolonged delays waiting for spontaneous passage of obstructive ureteroliths. In a recent report6 of management of cats with obstructive ureteroliths, the median interval from diagnosis to surgical management was only 3 days. If retrograde ureterolith movement is detected, surgery or lithotripsy should be considered because the urolith is possibly causing intermittent ureteral obstructions. One caveat is that if the urolith moves back into the renal pelvis, azotemia may improve or resolve. Surgical removal of uroliths without causing renal damage may be more difficult once the urolith moves retrograde into the renal pelvis. For removal of nephroliths in dogs, lithotripsy may result in less renal injury than nephrotomy.3,4
ABBREVIATIONS
| SWL | Shock wave lithotripsy |
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