Page 1217 - Clinical Small Animal Internal Medicine

123 Urolithiasis in Small Animals 1155

and include reocclusion, migration, or dysuria. In dogs, patients with staghorn calculi according to the American
VetBooks.ir ureteral stents have replaced standard surgery to Urologic Association Guidelines.
The author (AB) has performed endoscopic nephroli­
decompress upper urinary tract obstruction. Long‐
term complications include urinary tract infection
(26%), occlusion of the stent (9%), ureteritis (5%), stent thotomy in 11 dogs and one cat (16 renal units) using the
PCNL approach (n = 4 renal units) or SENL (n = 12 renal
migration (5%), encrustation (2%), and hematuria (7%). units) to remove complicated nephroliths (median diam­
More than three‐quarters of the patients were able to eter 2.5 cm; range, 0.5–5.7 cm). No kidney required
clear the infections if present before ureteral stent conversion to traditional surgical nephrotomy or
placement. In cats, ureteral stent placement can be nephrectomy. Median procedure time was 180 minutes
challenging and is associated with a 38% rate of long‐ (range, 90–270 minutes). Patients were discharged
term dysuria (responsive to steroid therapy). Since sub­ within 48 hours (range, 48–144 hours). The procedure
cutaneous ureteral bypass has been associated with was successful (resolution of complicated nephroliths) in
lower complication rates (see later) than ureteral stent­ 14 renal units. Ureteral stents were placed in all cases
ing in cats, it is now considered the treatment of choice during the PCNL/SENL and removed after 1–20 weeks
to relieve upper urinary tract obstruction in cats in the minimally invasively. No recurrence was reported during
authors’ practices. the follow‐up period (median duration 557 days).
Owners tolerated recovery from the SENL better than
Endoscopic Nephrolithotomy the PCNL because a nephrostomy tube was not required.
In humans, PCNL is typically performed for large or Overall, this series of cases demonstrates that PNCL
embedded nephroliths (>15–20 mm). In small animals, and SENL have a greater stone‐free rate (93% vs 85%)
PCNL/SENL is considered if ESWL fails or is not avail­ and lower recurrence rate (0% vs 10%) than ESWL for
able, cystine stones (which are resistant to EWSL) are large problematic nephroliths. The results of this study
present, or the stone is >15–20 mm (depending on suggest that the median survival time is higher for dogs
patient size). with IRIS stage 1, 2 or 4 disease treated with ENL com­
Typically, a combination of ultrasonographic, endo­ pared to previously reported survival times for the same
scopic, and fluoroscopic guidance is used for both PCNL IRIS stage diseases. However, further prospective studies
and SENL. PCNL has been performed in 11 dogs and are required to draw conclusions as this was only a small
one cat to date. The smallest patient to date having a number of cases.
PCNL/SENL was 5 lbs (2.3 kg), making patient size less
of an issue than other alternatives. Ureteroscopy
Typically, for PCNL, a renal access needle is used Contrary to human medicine, ureteroscopy is rarely per­
to access the renal pelvis through the greater curvature formed in veterinary patients. For minimally invasive
of the kidney under ultrasonographic guidance. treatment, dogs with a ureteral obstruction could have
Subsequently, a nephroscope is inserted through a sheath an endoscopic ureteral stent placed and/or may also
and into the renal pelvis to visualize the stone. If the lat­ undergo ESWL. If the patient is large enough (at least
ter is small enough, a stone retrieval basket is used to 39.6–44 lb [18–20 kg]), ureteroscopy can be considered.
remove the stone. If the stone is larger than the sheath, However, most dogs with ureterolithiasis are small ter­
intracorporeal lithotripsy (ultrasonic, pneumonic, elec­ rier or toy breeds, making this an uncommon procedure.
trohydraulic, or Ho:YAG laser) is used to fragment it. If this is to be performed, then the preplacement of a ure­
Once the stone fragments are small enough to fit through teral stent to allow for passive ureteral dilation, prior to
the sheath, they are removed and a locking‐loop nephros­ ureteroscopy, is typically recommended.
tomy tube (5 or 6 Fr) is left in place to allow the small
hole to seal and form a nephropexy. Subcutaneous Ureteral Bypass
Surgical‐assisted endoscopic nephrolithotomy can be Feline ureteroliths are typically more frustrating than
performed similarly to that described for PCNL, only the canine ureteroliths due to the small diameter of the feline
abdomen is opened to assist in nephrostomy access ureter (<0.4 mm) and the endoscopic and surgical limita­
closure, to prevent the need for a nephrostomy tube. tions. In cats, ESWL is not typically advised and ureter­
For both PCNL and surgical‐assisted endoscopic oscopy is not possible.
nephrolithotomy, because a balloon is used to dilate the A subcutaneous ureteral bypass (SUB) involves the
renal parenchyma (no incision is performed), minimal placement of a nephrostomy tube and a cystostomy tube
nephron loss occurs. PCNL and SENL are considered that are connected subcutaneously to a shunting port,
the most “kidney‐sparing” procedures with the highest allowing for urine drainage from the kidney directly to
urolith‐free rate and minimal effect on GFR. For these the bladder, bypassing the ureter (Figure 123.19). Initially,
reasons, they are recommended as the first treatment for this procedure was primarily performed for cats with