Nephrolithiasis and ureterolithiasis in the canine and feline medical and surgical patient (Proceedings)

The prevalence of renal and/or ureteral calculi in the dog is relatively uncommon (5-10% of all urinary tract calculi) when compared to calculi in the lower urinary tract. The true rate of occurrence is likely unknown and/or under diagnosed since renal calculi may not cause clinical signs.

Breeds with higher incidence of uroliths are miniature schnauzer, dachshund, Dalmatian, Yorkshire Terriers, and Shih Tzus. Some uroliths occur more often in selected breeds such as urate (Dalmatian), cystine, (dachshund, English bulldog), calcium oxalate (miniature schnauzer, poodle, Yorkshire Terrier, Lhaso apso).

Pathophysiology

Several factors interact in a complex fashion to cause the formation of urinary calculi; these factors are 1) Supersaturation of urine with a given substance resulting in crystal formation 2) Inhibitors of crystallization probably decrease in quantity 3) Crystalloid complexors appear 4) Promoters of crystal growth and aggregation increase.

Medical therapy to treat urolithiasis is designed to change the state of oversaturation to a state of undersaturation of various minerals. Increasing the fluid content of urine or increasing substances such as citric acid that complex with minerals are examples of decreasing these substances.

Clinical Signs

Depends upon size, location, and number of stones, as well as whether there is infection/pyelonephritis, and/or urinary tract obstruction. Some animals have NO clinical signs and the stones are discovered incidentally on abdominal radiographs. This is also potentially true if the animal has only one kidney affected by disease.

-Sublumbar/abdominal pain, not commonly recognized

-Hematuria

-Recurrent urinary tract infections

-Renal failure

Vomiting Inappetence

Depression Weight loss

Frequency of Stone Occurrence

Calcium Oxalate = 41%

Struvite = 33%

Ammonium Urate = 12%

Mean Age of Occurrence= 6-9 years

I. Diagnostic Work-Up

-Minimum data base

CBC.........................Urinalysis

Chemistries................Urine Culture

**-Excretory Urography= Crude estimation of renal function, NOT quantitative MUST PREPARE PROPERLY (Fasting for 24 hours & enemas the evening before and morning of the study)

Place an intravenous catheter and administer 1mg Iodine per lb body weight (Max 60 mg) unless the animal is azotemic then must increase the dose

-Ultrasound, while valuable does not provide me the information regarding possible obstruction I'm comfortable with thus I prefer Excretory urography

-Nuclear Scintigraphy is the ONLY way to measure INDIVIDUAL kidney function, this involves a nuclear scan and is not widely available but is valuable in making treatment decisions especially when bilateral disease is present

-Prediction Of Stone Type

Crystalluria................Size

UTI?.........................Single vs multiple

Radiographic appearance

II. Medical Management/Dissolution

Either dissolution (if possible) OR prevention of growth of nephroliths MAY be achieved by medical management

A. Calcium Oxalate

a. No protocol for dissolution BUT prevention of growth may be advantageous

b. Diagnose and treat any cause of hypercalcemia; i.e.Primary Hyperparathryoidism

c. Eliminate any acidifying diet or glucocorticoid usage

d. Canine Diet U/D

e. Consider use of oral potassium citrate for acidification

f. Thiazide diuretics, controversial efficacy and electrolytes must be monitored

B. Struvite

a. May require a prolonged period of therapy

b. Calculolytic diet (S/D)

i. Protein deficient

ii. High sodium and chloride levels

c. Antibiotic therapy, continued as long as stones are radiographically visible

C. Urate

a. Calculolytic diet (U/D)

b. Allopurinol 15 mg/kg q12h

c. Consider use of sodium bicarbonate (25-50 mg/kg q12h) or potassium citrate (50-150mg/kg q12h

d. Eradicate UTI

e. Consider whether the dog may have a portal vascular anomaly (shunt)

Surgical Indications

**- No simple or black & white answers

Some indications for surgical removal include:

• Obstruction

• Hydronephrosis

• Hydroureter

• Renal Failure –Is It Cause And Effect Or Coincidental?

• Infection (Persistent)

• Stone In 1 Functional Kidney

Factors to consider BEFORE making the decision for surgery:

• Is medical therapy possible? (stone type?)

• Over-all health of the animal?

• Is the animal a candidate for "watchful waiting"?

Stone or stones in the renal pelvis that is NOT causing obstruction and NOT associated with infection MAY be a candidate for maintenance therapy with CAREFUL observation for stone growth or development of obstructive disease.

III. Surgery

A. Nephrotomy

Until recently, it was thought that nephrotomy inevitably resulted in decreased renal function (20-50%) following nephrotomy. Recent research does NOT substantiate this fact at least in dogs with normal kidney function. We do NOT know the effect of nephrotomy on a patient with decreased glomerular filtration rate (GFR).

Consider use of mannitol n the immediate preoperative period to act as an osmotic diuretic and potentially preserve renal function in a kidney that has decreased glomerular filtration rate.

1. Expose the appropriate kidney by using the duodenum and mesoduodenum on the right side or the colon and mesocolon on the left side.

2. Dissect and isolate the renal artery which is located rostral and slightly dorsal to the EASILY visualized renal vein; the renal vein is the most easily visualized. Place either a bull-dog clamp or a Rumel tourniquet on the renal artery.

3. Mobilize the kidney as necessary to make an incision on the convex surface of the kidney. The incision is generally about 2/3rd s the length of the kidney. Use the back of the scalpel handle to bluntly separate renal parenchyma down to the stone located in the renal pelvis.

4. Remove the stone (s) and submit for calculi analysis.

5. Pass a catheter into the proximal ureter to assure patency.

6. Hold the half's of the kidney together and close the capsule using 4/0 PDS or Maxon on a tapered needle with a continuous pattern. Take care as the capsule easily tears; you might take a small bite of renal parenchyma along with capsule if suture holding is problematic.

7. Remove the tourniquet and ensure there is no major bleeding from the Kidney. If major hemorrhage ensues use one or two mattress sutures through the kidney to achieve hemostasis.

B. Pyelolithotomy

This is a nice technique as it spares renal parenchyma however the \stone must be in the proximal dilated ureter for this to be possible. (Rarely possible in my experience)

IV. Lithotripsy

A. ECSWL= Extracorporeal shock wave lithotripsy

This is the method of choice for treatment of kidney stones in man. The technique is becoming more popular and available in veterinary medicine. Best part is the non-invasive nature of the treatment.

1. Non-invasive; repetitive application of shock waves to the stone results in gradual (over 24-48 hours) breakdown of the stone and passage of the fragments/powder in the urine.

2. "Wet" lithotripsy utilizes a water bath to augment shock waves; "Dry" lithotripsy does not require a water bath, shock waves or augmented by passage through gel filled containers.

3. Sedation in man but general anesthesia is used for animals

4. Most of the work in animals has been done by Dr. Larry Adams at Purdue University, Dr. India Lane also offers lithotripsy at U of Tennessee.

5. About one-third of animals require 2 separate treatments for complete breakdown of stones.

6. NOT very effective for bladder stones and usually only attempted when kidney stones are being done concurrently.

7. Has NOT been successful in general for feline kidney stones. Feline kidney seems more sensitive to damage than the canine.

B. EHL = Electrohydraulic lithotripsy

1. This can be used for bladder stone dissolution.

2. Equipment not widely available in veterinary medicine.

V. Ureterotomy

Ureteral stones are uncommon in the canine. They are common in humans and cause excruciating back pain as a result of "ureteral colic". Ureteral calculi are also common in cats and are almost always calcium oxalate. Indications for stone removal include ureteral obstruction and a functional kidney. Options include

A. Ureterotomy

1. Relatively straight forward IF the ureter is dilated.

2. Longitudinal incision over the stone with removal and closure of the ureter with 5/0 monocryl on a tapered needle. The ureter should be mobilized and free from the retroperitoneal space. A sterile tongue depressor is used for "backing" as the incision is made into the ureter. Following stone removal, the ureter is catheterized both proximally and distally to assure patency.

3. Simple closure or closure transversely after a longitudinal incision is advocated by some to decrease the risk of stricture.

4. I have also removed ureteral calculi by passing stone "baskets" retrograde from the bladder by catheterizing the ureteral orifice. This obviates the need for incision into the ureter and in theory may decrease the risk of stricture.

Feline Upper Urolithiasis

The composition of uroliths affecting the feline urinary tract has changed dramatically over the past 20 years. Feline urethral obstruction caused by mucus and matrix plugs or magnesium ammonium phosphate (MAP) stones have declined in overall ocurrence while numbers of nephroliths and ureteroliths have increased. The most common type of nephrolith and ureterolith in cats is calcium oxalate.

University of Minnesota Urolith Center :

Magnesium Ammonium Phosphate (MAP) 1981=78% 1999= 32%

Calcium Oxalate (CA OXL) 1981= 1% 1999= 55%

Feline Urethral Obstruction/Purdue Data Base

1980= 13.8 /100 cases

1988=5.8/1000 cases

1997=4.3/1000 cases

*Numbers of perineal urethrostomies in cats has likewise decreased dramatically

Feline Nephroliths/Ureteroliths

Increased numbers in 1990's

Challenging disease

Significant morbidity, mortality and renal disease

Geriatric male cats of Himalayan, Persian, or Bermese origin cited as being more common but population has become more normalized

Calcium oxalate stones caused by hypercalciuria and/or hyperoxaluria. Factors predisposing to this include:

Hpercalciuria...............................Hyperoxaluria

Excess dietary calcium...................Excess dietary oxalate

Excess dietary sodium....................Excess vitamin C

Hypercalcemia..........................Pyridoxine deficiency

Aciduria

*Hypercalcemia present in 1/3 rd of cats??

The effects of diet calcium and oxalate are largely unknown in cats however the acidifying diets that promoted the decrease in MAP uroliths promotes an acid urine that precipitates calcium oxalate in the urine. Magnesium normally inhibits the formation of CAOXL thus low magnesium content diets have been implicated as causative in oxalate stone formation. This is likely an oversimplification but the predisposing factors of diet cannot be ignored; other factors have also been implicated including those listed below:

RISK FACTORS..................NON-RISK FACTORS

-Urine acidifying diets..................-Body weight

-Single brand of cat food..................-Source of water

-Indoor environment..................-Feeding pattern

-Persian breed

Kirk & Ling JAVMA, 207, 1429, 1995

Feline Nephroliths/Ureterolithiasis

-Calcium oxalate= 43%

-Matrix= 25%

-Calcium phosphate 15%

Clinical Signs

-Nephroliths or ureteroliths may be asymptomatic (incidental findings)

-Pyelonephritis or Chronic renal failure, causative or concurrent in some cats

-Recurrent urinary tract infections

-Ureteroliths

Lethargy............Vomiting

Weight loss............Pain?? (rare compared to man)

Diagnostic Evaluation............Diagnostic Evaluation Imaging

-CBC.......................................-Abdominal radiography

Anemia in CRF...............................MOST stones radiopaque

.................................................-Excretory urography

-Serum Biochemistry............-Ultrasonography

R/O hypercalcemia............Hydronephrosis, Hydroureter

Renal failure?............-Antegrade Pyelography

-UA/Culture............Morbidity, Ultrasound guided

................................-CT scan

............................# and location of stones

................................. ...Differentiate pelvic mineralization & nephroliths

.................................... -Scintigraphy

Anatomic Location.................Feline Ureteral Surgeries

-Renal Pelvis (18).................-Ureterotomy

-Proximal Ureter(19).................-NephrectomyUreterectomy

-Middle ureter (14).................-Ureteroneocystostomy

-Distal ureter (7).................** -Operating microscope/experience required

-Bladder (1).................-High morbidity

Nephrolith/Ureterolith Treat.................Nephrolith/Uretero Med

-NONE in some cases.................-No dissolution protocols

"Watchful waiting".................-48-72 hours IV fluids

-Nephrotomy or Pyelolithotomy.................- Diuretics

-Nephrectomy/Ureterectomy.................-Distal ureterolith more likely to pass

-Ureterotomy.................-Duration??

-Ureteroneocystostomy.................-Diet

-Lithotripsy

Disappointing results so far but "dry" lithotripsy may have a place.

Diet/Pharmacology.................Surgery Indications

-Diets.................-Renal outflow obstruction

C/D –OXL.................-Complete ureteral obstruction

pH/O.................-Persistent UTI

-Pharmacology.................-Failure of ureterolith to move?

Potassium citrate.................Some ureteroliths imbed in wall & are not obstructing

Hydrochlorthiazide

Vitamin B6

-Stage nephrotomies at 4-6 week intervals if bilateral surgery is indicated. Operate most functional kidney first

-Place gastrostomy tube intraop

Surgical Problems

-Renal function often compromised preoperatively

-Effects of nephrotomy itself MAYfurther compromise function although this has not been shown in the cat

-Possible anemia pre and postop (cross-match and prepare for transfusion)

-Ureterotomy and bladder reimplantation techniques may be associated with stricture/stenosis, SMALL URETER SIZE

Upper urinary tract urolithiasis is a difficult problem for us to deal with without causing additional morbidity for the reasons discussed. I avoid surgery whenever possible and elect watchful waiting for the reasons mentioned. Cats should be monitored every 3-6 months for recurrence or progression of disease.