Management of uroliths in the lower urinary tract: Alternatives to cystotomy - Michigan ...

Management of uroliths in the lower urinary tract:
                    Alternatives to cystotomy
             Larry G. Adams, DVM, PhD, Diplomate ACVIM (SAIM)
  Purdue University College of Veterinary Medicine, West Lafayette, Indiana, USA
Key points:
Minimally invasive techniques for management of uroliths include medical
dissolution, voiding urohydropropulsion, cystoscopic basket extraction, laser
lithotripsy and laparoscopic-assisted cystotomy.
Struvite uroliths can usually be dissolved rapidly using dietary therapy in cats.
Prevention of urolith recurrence should be based on quantitative urolith analysis
performed by a veterinary urolith center.
Calcium oxalate uroliths are highly recurrent and early detection of recurrence may
allow for removal by voiding urohydropropulsion.
Introduction
“To cut is to cure” should not be the veterinarian’s mindset when approaching
uroliths. Effective management of urolithiasis involves both removal of the uroliths
and prevention of recurrence. Removal of bladder and urethral stones has
traditionally been performed by open cystotomy and urethrotomy. While surgical
removal is usually effective for uroliths in the bladder and urethra, post-operative
radiographs should always be performed to confirm complete removal. Uroliths may
be inadvertently left in the urinary tract in 10-20% of dogs following open cystotomy,
with the majority of the uroliths remaining in the urethra. These remaining urethroliths
may be removed by laser lithotripsy or basket extraction to avoid an additional
surgery. Minimally invasive management techniques often can be used to replace
open surgical removal of uroliths. Minimally invasive techniques include medical
dissolution, voiding urohydropropulsion, cystoscopic basket extraction, laser
lithotripsy and laparoscopic-assisted cystotomy. Prevention of recurrence should be
based on quantitative urolith analysis from a veterinary urolith center.
The decision about which approach to pursue for urolith removal is influenced by
multiple factors including the potential for medical dissolution of the suspected urolith
type, number and location of uroliths, clinician experience with minimally invasive
options, owner preferences and availability of specialized equipment.
Medical dissolution
Medical dissolution is effective for some uroliths locations and types. Urocystoliths
and nephroliths are amenable to dissolution whereas ureteroliths and urethroliths are
not without additional procedures. Struvite, urate, and cystine uroliths may be
medically dissolved whereas calcium oxalate, calcium phosphate, silica and
compound uroliths cannot be medically dissolved. For dissolution to occur, uroliths

must be surrounded by under-saturated urine to allow the crystals to go back into
solution. Medical dissolution of urocystoliths in male dogs is associated with risk of
urethral obstruction once the uroliths are small enough to pass into the urethra;
however, dissolution is often successful without urethral obstruction. The risk of
leaving uroliths in the urinary tract after cystotomy is likely higher than the risk of
urethral obstruction during dissolution of uroliths.1
Struvite uroliths in dogs are usually infection-induced from infection to urease
producing bacteria. Over 90% of struvite stones in dogs are caused by UTI with
Staphylococcus and Proteus. Other urease-producing organisms that infrequently
cause struvite uroliths include Pseudomonas spp, Klebsiella spp, Corynebacterium
urealyticum and mycoplasmas such as Ureaplasma urealyticum.2 Medical
dissolution of infection-induced struvite urocystoliths requires a combination of
appropriate antimicrobial and calculolytic dietary therapy. Antimicrobial selection
should be based on urine culture obtained by cystocentesis prior to antimicrobial
therapy. Antimicrobial therapy must be given throughout the entire dissolution period
because viable bacteria are contained within the layers of struvite uroliths.
Commercial diets that aid in dissolution of struvite uroliths in dogs include Hill’s
Prescription diet s/d, Hill’s Prescription diet c/d, Purina UR, and Royal Canin S/O
Lower Urinary Tract Support Diet. Antimicrobial and dietary therapy should continue
approximately 1 month beyond radiographic resolution of struvite urolithiasis or until
resolution of uroliths on ultrasonography. One week after initiation of antimicrobial
therapy, urine should be obtained by cystocentesis for urinalysis and culture.
Urinalysis should reveal decrease of the urine pH to

saline via cystoscopy or urethral catheterization. The dog is positioned so that the
spine is roughly 25 degrees caudal to a line perpendicular to the effects of gravity,
such that a line drawn through the urethra into the bladder is approximately vertical.
The bladder is agitated side to side to cause the urocystoliths to settle in the trigone
by gravity. The bladder is palpated and the intravesicular pressure is gradually
increased by manual compression of the bladder to initiate a detrusor contraction.
Once voiding begins, the bladder is compressed more firmly to attempt to maintain
maximum urine flow to flush out the cystoliths. The bladder is refilled with sterile
saline through the cystoscope or a urinary catheter and the process is repeated until
no urocystoliths are passed with the expelled fluid. Then post-procedural
radiographs or cystoscopy are performed to confirm complete removal of the
urocystoliths. Digital flexible ureteroscopes and high definition cameras for rigid
cystoscopes permit visualization of smaller uroliths than digital radiographs and may
eliminate the need for post-procedural radiographs.
Laser lithotripsy
If available, laser lithotripsy using the holmium: YAG laser is an option for
fragmentation of cystoliths that are too large for voiding urohydropropulsion. 4 The
holmium laser energy is absorbed in

may be responsible for up to 9% of recurrent urolith cases Therefore preventative
measures such as diet and medications should be utilized to reduce the risk of
recurrence. Dietary changes should be attempted; additional medications are
recommended if there is persistent calcium oxalate crystalluria or recurrence of
calcium oxalate urolithiasis. Increased water intake though feeding a canned diet or
by adding water to the diet may be the most important recommendation to help
prevent recurrence of calcium oxalate urolithiasis in dogs.
The commercial diets recommended to reduce the risk of calcium oxalate urolith
recurrence in dogs include Royal Canin Canine Urinary S/O Diet, Purina UR, and
Hill’s Prescription diet c/d MultiCare. Dietary therapy alone will not always prevent
calcium oxalate urolith recurrence. Hydrochlorothiazide (2 mg/kg PO q12h) should
be considered in dogs that have persistence of calcium oxalate crystalluria or
recurrence of calcium oxalate urolithiasis despite diet therapy. Thiazide diuretics
cause subclinical volume depletion resulting in increased proximal tubular
reabsorption of sodium and calcium. Once dietary and hydrochlorothiazide therapy
have been implemented, if calcium oxalate crystalluria is persistent or calcium
oxalate uroliths recur, potassium citrate should also given to adjust the urine pH to
6.5—7.0 using a starting dose of 50—75 mg/kg PO q12h. The serum potassium
should be initially monitored initially with potassium citrate supplementation and the
dose reduced if hyperkalemia occurs.
Because calcium oxalate uroliths commonly recur, appropriate surveillance using
radiographs should be utilized to document recurrences before the uroliths become
too large to void. If small recurrent urocystoliths are diagnosed, many recurrences
may be managed by voiding urohydropropulsion. Avoiding cystotomy and closure of
the bladder with sutures eliminates the risk of suture-associated urolith recurrence,
which may be responsible for up to 9% of recurrent urolith cases. 9 Suture-associated
uroliths are usually S or C shaped and may be attached to the bladder wall in some
cases.
When the appropriate option is “watchful waiting”
Asymptomatic dogs and cats with non-dissolvable uroliths too large to pass into the
urethra or too irregular to cause a urethral obstruction may need only periodic
monitoring and appropriate client education.1 Likewise, non-dissolvable uroliths
smaller than 1 mm don’t require removal by voiding urohydropropulsion until the
uroliths enlarge enough to justify an intervention at a later date. For these situations,
periodic monitoring with abdominal radiographs every 3-6 months may be the most
appropriate plan.

Table 1. Guidelines for selection of minimally invasive options (modified from reference 7)
 Procedure        Urolith size limit     Patient size limit    Equipment           Comments and
                                                               required            limitations
 VUH              Male dog: 2 mm         Any size patient      -Urinary catheter   Often easier to fill
                  Female dog: 3-4 mm                           for male dogs       the urinary
                                                               -Rigid cystoscope   bladder using a
                                                               or urinary          rigid cystoscope in
                                                               catheter for        female dogs
                                                               female dogs         rather than repeat
                                                                                   urethral
                                                                                   catheterization.
 Basket           Male dog: 2-3 mm       Large enough to       Cystoscope and      The operator
 extraction via   Female dog: 4-5 mm     accept an             various sized       should be
 cystoscopy                              appropriately         stone baskets       prepared for laser
                                         sized cystoscope                          lithotripsy.
 Laser            Male dog: 5 mm         Must be able to       Various             1)

8.   Runge J, Berent A, Weisse C, Mayhew P. Transvesicular percutaneous cystolithotomy
     for the retrieval of cystic and urethral calculi in dogs and cats: 27 cases (2006-2008). J
     Am Vet Med Assoc 2011; 239:344-349.
9.   Appel SL, Lefebvre SL, Houston DM, et al. Evaluation of risk factors associated with
     suture-nidus cystoliths in dogs and cats: 176 cases (1999–2006). J Am Vet Med Assoc
     2008;233:1889–1895.