Because of the positive Staphylococcus species urine culture results with staghorn stones in both renal pelves and an elevated urine pH, the cause of the azotemia
is likely related to chronic pyelonephritis that is associated with struvite nephrolithiasis. Typically, if stones are made
of struvite, or magnesium ammonium phosphate, they can be medically dissolved with a dissolution diet (either acidifying or
neutralizing) and appropriate antibiotic therapy. This must be followed strictly for effective dissolution. For nephroliths,
it can take three to nine months for appropriate dissolution. Many struvite nephroliths contain some calcium apatite or a
calcium oxalate shell and, thus, will not dissolve well.
A radiographic examination and a urine culture should be performed every month to confirm no bacterial growth and the stones
are not getting larger. If by three months the stones are not getting smaller, then removal may be necessary.
This patient was followed for five months with serial negative urine cultures and radiographs. The nephroliths did not change
in size, and minimally invasive removal was elected with the use of staged bilateral percutaneous nephrolithotomy (PCNL) scheduled
six weeks apart. With the use of intracorporeal ultrasonic lithotripsy, the stones were able to be successfully removed without
complication, avoiding a nephrotomy.
The left side was treated first, and the entire stone was able to be removed through a small sheath using nephroscopy and
lithotripsy. A ureteral stent was then placed prophalactically to prevent any edema or fragments from obstructing the ureter.
Six weeks later, the same procedure was done on the right side. Four weeks after both kidneys were completed, the patient
underwent a cystoscopy for bilateral ureteral stent retrieval.
Over the course of the following year and a half, there were no recurrent urinary tract infections, no uroliths were detected
on serial radiographic or ultrasonographic examinations and the creatinine concentration improved to 1.2 mg/dl. The dog was
maintained on a neutralizing stone diet.
In the past, nephroliths were treated medically, via dissolution, or removed by surgical nephrostomy, nephrectomy or pyelotomy.
Management of calculi can be challenging in small animals as the incidence of stone recurrence in dogs and cats is high. Many
canine and feline nephroliths remain static in size and clinically silent for years.
Some controversy still exists as to whether nonobstructive kidney stones worsen underlying kidney disease. Their removal is
typically recommended if the stones are growing, if there is a partial or complete ureteropelvic junction obstruction resulting
in progressive hydronephrosis or if renal parenchymal loss, worsening renal function, chronic hematuria, pain or recurrent
infections are occurring.
Limitations of nephrotomy
In small animals, traditional surgical interventions are met with complications that can be severe and life-threatening. Nephrotomy
has been associated with severe hemorrhage, decreased renal function, ureteral obstruction cause by nephrolith remnants and
In a study in normal cats, there was a 10 to 20 percent decrease in the glomerular filtration rate (GFR) of the ipsilateral
kidney after a nephrotomy. This was clinically insignificant in normal cats, but in a clinical patient that has maximally
hypertrophied the remaining nephrons because of prior nephrolith-induced damage, the significance could be dramatic. So patients
with an already compromised GFR from chronic stone disease may develop a clinically significant decline in renal function.
Also, since more than 30 percent of adult cats will develop chronic kidney disease in their lifetime, resulting in a 67 to
75 percent decline of renal function, these cats cannot tolerate a 10 to 20 percent further decline in GFR from a nephrotomy.
Hence, this procedure should ultimately be avoided whenever possible. Similar studies have not been done in clinical dogs
to date—only normal dogs without exhausted hypertrophy mechanisms have been studied, which would not be considered clinically
equivalent to our patient population.