Page 1213 - Clinical Small Animal Internal Medicine

123 Urolithiasis in Small Animals 1151

In a study of normal cats, the GFR of the ipsilateral kid­ When ureterotomy or ureteroneocystotomy is unsuc­
VetBooks.ir ney decreased by 10%–20% after a nephrotomy. This was cessful, a ureteronephrectomy may be required, which is
not ideal due to the high risk of subsequent stone‐
clinically insignificant in normal cats but in a clinical
patient with maximally hypertrophied nephrons due to
majority of cats being azotemic at the time of diagnosis
prior nephrolith‐induced damage, the significance could induced obstruction of the contralateral kidney and the
be dramatic. Therefore, feline patients with an already with a unilateral ureteral obstruction. Chronic kidney
compromised GFR from chronic stone disease may disease is common in cats when a ureteral obstruction
develop a clinically significant decline in renal function is diagnosed, with 75–97% of cats with a unilateral
after nephrotomy. Since over 30% of adult cats eventually obstruction reported to be azotemic. For this reason,
develop chronic kidney disease associated with a 75% removing a kidney for a diseased ureter should never be
decline of renal function, a 10–20% further decline in encouraged.
GFR from a nephrotomy may be poorly tolerated. Hence, Another major concern is that in one study, 40% of cats
nephrotomy should be avoided when possible in all cats, developed a second ureteral obstruction over a 1–2‐year
especially those with existing renal disease. In dogs follow‐up, and of these cats, 62% had evidence of neph­
undergoing traditional surgery for nephrolithiasis, there rolithiasis documented at the time of the first surgery.
was a very high complication rate (23%) following the Unfortunately, removing a nephrolith in a cat is chal­
procedure, as well as remaining fragments in more than lenging and potentially harmful, and it is impossible to
40%. In addition, 67% of dogs undergoing nephrectomy predict whether a nephrolith will become an obstructive
developed renal azotemia. ureterolith, so nephrotomy should not be encouraged.
Typically, unless the stone results in a ureteral obstruc­ Results after ureterotomy, pyelotomy, and/or uretero­
tion or severe perisitent hematuria, is the cause of nephrectomy have been reported in 16 dogs. The mor­
chronic UTIs, or is so large that it is overtaking the renal tality rate (death related to azotemia or to clinical signs
parenchyma, nephroliths remain clinically silent for the related to the urinary system) in this study was 25% (4/16
life of the dog or cat and removal is currently not being dogs). Of the 12 dogs that were followed, 17% required
recommended. The 2016 ACVIM consensus statement an additional surgery within four months for ureteral
on the management of urinary tract stone disease rec­ stricture or recurrent ureteroliths. Most dogs (88%) had
ommends management of upper urinary uroliths by urinary tract infections at diagnosis, and 50% had con­
minimally invasive techniques rather than standard sur­ current nephrolithiasis. Ten (62.5%) dogs presented to
gery when possible. the hospital with elevated blood urea nitrogen and/or
creatinine concentrations and 50% remained elevated
Ureteroliths after successful surgery. Postoperatively, two dogs had
Traditional surgical intervention to address ureteroliths worsening azotemia.
includes ureterotomy, neoureterocystostomy, ureterone­
phrectomy, or renal transplantation. Kyles et al. reported Minimally Invasive Management
procedure‐associated complication and mortality rates of Nephroliths and Ureteroliths
of >30% and 18–38%, respectively, in more than 150 cats
that underwent at least one of these procedures. These In humans, minimally invasive procedures are the treat­
cases were seen at two universities where microsurgical ment of choice for nephrolithiasis and ureteroliths
expertise was available and a renal transplant program due to the high complication rates and morbidity asso­
existed. The morbidity and mortality rates may be ciated with traditional surgery (Table 123.4). These
higher in environments where operating microscopes procedures include ESWL for nephroliths <1–2 cm and
and microsurgical experience and expertise are not endo scopic nephrolithotomy (percutaneous nephroli­
available. thotomy [PCNL] or surgically assisted endoscopic neph­
Many of the complications associated with surgery are rolithotomy [SENL]) for nephroliths >1–2 cm. Open
due to site edema, recurrence of stones that then pass surgery and laparoscopy are typically only considered
from the renal pelvis to the surgery site, stricture forma­ after other less invasive options have failed or been deemed
tion, persistent obstructions, missed ureteroliths, and inappropriate.
ureterotomy‐associated or nephrostomy tube‐associated Over the last 10 years, evidence‐based data support
urine leakage. In the Kyles et al. study, patients that that minimally invasive treatment of upper urinary tract
underwent a ureterotomy for treatment of a ureteral uroliths in dogs and cats is associated with a lower mor­
obstruction (the most commonly performed procedure bidity and mortality rate compared to surgical proce­
in practice) had a perioperative mortality rate of 25%. dures. Selection of the most kidney‐sparing procedure
Uroabdomen occurred in 15% of cats in which a uretero­ should always be a priority to treat upper urinary tract
neocystotomy was performed. uroliths in small animals.