Page 1183 - Clinical Small Animal Internal Medicine
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122  Obstructive Uropathy  1121

               right ureteral obstruction. In addition, it had a severely   devices are commercially available. Subcutaneous ure­
  VetBooks.ir  shrunken left kidney, which was likely nonfunctional.   teral bypass employs a nephrostomy tube and a cystos­
                                                                  tomy tube, which are connected to a dual‐lumen vascular
               After placement of the right ureteral stent, the cat was
               discharged four days later with a BUN of 16 mg/dL and a
                                                                  wall. This port allows the system to be flushed at regular
               creatinine of 1.4 mg/dL.                           port that is attached under the skin to the ventral body
                 In the authors’ experience, ureteral stents in cats pro­  intervals to avoid obstruction and facilitates urine sam­
               vide acute resolution of the obstruction but have a mod­  pling (see Figure 122.11). At many centers, subcutaneous
               erate risk for ureteral irritation and pollakiuria that can   ureteral bypass devices are now the treatment of choice
               be challenging to manage. Studies suggest one‐third of   for obstructive urolithiasis in cats but are rarely implanted
               cats with a ureteral stent will have dysuria either tran­  in dogs where conventional surgery or temporary ureteral
               siently or permanently and that 19% of feline ureteral   stenting are often effective. Long‐term complications of
               stents will become obstructed. There is also an increased   ureteral bypass devices include infection and biofilm for­
               risk of ascending urinary infection with a stent in place.   mation, encrustation and obstruction, and rarely signs of
               In human medicine, ureteral stents are left in place for   dysuria. The rate of complications appears lower in cats
               only 3–4 months in most cases to avoid stent encrusta­  with a subcutaneous ureteral bypass device than was
               tion and calcification. However, stents have been left   observed  with ureteral stents  but routine surveillance
               indwelling in cats for greater than five years that were   (imaging, system flushing, urine culture) is still required.
               seemingly well tolerated (see Figure  122.10). In dogs,   For animals with ureteral obstruction secondary to
               ureteral stents for benign ureteral obstructions are well   urothelial malignancy, ureteral stenting is advised to
               tolerated,  can  be  placed  cystoscopically,  and  are  often   deobstruct the kidney and restore urine flow. In the dog,
               removed once the obstructive stone has passed, avoiding   this is done via percutaneous transabdominal access to
               long‐term risk for stent dysfunction. The presence of a   the dilated renal pelvis with a small needle, through
               ureteral stent induces passive ureteral dilation which   which a wire is advanced under fluoroscopic guidance to
               may allow a previously obstructive urolith to pass, after   the site of obstruction (Figure 122.12).
               which the stent can be removed via an outpatient cysto­  The wire is manipulated through the obstruction, into
               scopic procedure. Currently, the authors monitor ani­  the bladder, and out the urethra. The stent is then
               mals with ureteral stents every 3–4 months by imaging   advanced over this wire and into place within the renal
               and  urine  culture.  If  stent  malfunction  develops,  evi­  pelvis proximally and the bladder distally and urine now
               denced by recurrent infection, pollakiuria, obstruction,   flows through the stent lumen, bypassing the neoplastic
               abdominal  pain, or stent migration/fracture,  then the   obstruction. A small series of 12 cases found that percu­
               stent is removed via cystoscopy or cystotomy.      taneous stent implantation for trigonal urothelial carci­
                 To avoid eventual dysuria and potential complications   noma was feasible in all dogs and the stents remained
               of a ureteral stent in cats, or for those animals in which a   patent for the remainder of the animals’ lives, which
               stent cannot be placed, subcutaneous ureteral bypass   ranged from 0.25 to 11 months.


               (a)                              (b)                               (c)




















               Figure 122.12  Fluoroscopic images from an 8‐year‐old Labrador retriever with urothelial neoplasia causing ureteral obstruction. (a) Direct
               puncture of the renal pelvis was obtained and a wire was advanced down the dilated ureter to the site of obstruction at the
               ureterovesicular junction. (b) With manipulation, the wire is advanced across the obstruction and into the bladder. (c) The stent has been
               positioned throughout the length of the ureter with one pigtail in the renal pelvis and one in the bladder, allowing restoration of urine
               flow past the malignant obstruction.
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