135

Surgical Management of Pediatric

Stone Disease

Francis X. Schneck

Questions

1.Which component(s) of present-day Western diets is(are) thought to contribute to the increasing prevalence of nephrolithiasis in the pediatric population?

a.Protein

b.Potassium and magnesium

c.Saturated fats and cholesterol

d.Sodium and carbohydrates

e.Calcium

2.A 5-year-old boy is seen in the office with complaints of intermittent right flank pain. There have been no episodes of nausea, vomiting, or fevers. He has 3 + blood on a urine dip. His physical exam reveals some mild right costovertebral angle (CVA) tenderness. Which imaging modality should be used first?

a.Magnetic resonance imaging (MRI)

b.Plain radiograph, kidney-ureter-bladder (KUB)

c.Ultrasound

d.Computed tomography (CT) scan

e.Retrograde pyelogram

3.A 12-year-old girl is found to have a 5-mm left distal ureteral stone after an acute episode of left flank pain. She responded well to conservative therapy (intravenous [IV] hydration and pain medication) and her pain subsides. The next step in management is:

a.given the size of the stone, it will most likely pass in 6 weeks.

b.given the size of the stone, it will most likely not pass, and planning for

an endourological procedure is advisable.

c.given the size of the stone, it will most likely not pass, but a trial of oral therapies such as alpha-blockers and steroids may facilitate stone passage.

d.given the size of the stone, it will most likely not pass, but a trial of oral therapy with a calcium channel blockers may facilitate stone passage.

e.the stone has most likely passed, and no further interventions will be needed.

4.A 10-year-old male with spina bifida had an augment cystoplasty, bladder neck reconstruction, and bilateral Glenn-Anderson ureteral reimplantation for high-grade reflux at age 7 years. He was found to have a 1-cm renal pelvic stone. The therapy least likely to yield an efficacious (stone-free) result is:

a.shockwave lithotripsy (SWL).

b.ureteroscopy with laser lithotripsy.

c.ureteral stenting and ureteroscopy with laser lithotripsy 6 weeks later.

d.percutaneous nephrolithotomy (PCNL).

e.open pyelolithotomy.

5.With regard to SWL in the treatment of pediatric nephrolithiasis, treatment failures are associated with:

a.high stone burdens (i.e., 2-cm calcium oxalate monohydrate stone).

b.sizeable infundibular length.

c.an infundibulopelvic angle greater than 45 degrees.

d.staghorn calculi.

e.a, b, and c.

6.Complications that may occur during ureteroscopy while treating a ureteral stone include:

a.hypothermia and hyponatremia.

b.ureteral avulsion.

c.hypertension.

d.all of the above.

e.a and b.

7.A 9-year-old female with cystinuria is found to have a right 2-cm renal pelvic stone. The best treatment option to treat her stone is:

a.extracorporeal SWL (ESWL).

b.ureteroscopy with laser lithotripsy and stone basketing.

c.PCNL.

d.medical therapy with potassium citrate and tiopronin.

e.anatrophic nephrolithotomy.

8.The most common chemical composition of a bladder stone found in a child from a developing country would be:

a.struvite.

b.ammonium acid urate.

c.uric acid.

d.calcium oxalate monohydrate.

e.calcium oxalate dehydrate.

Answers

1.d. Sodium and carbohydrates. It has been speculated that diets rich in sodium and carbohydrates may be a contributing factor to the etiology of urolithiasis in this cohort of children.

2.c. Ultrasound. Ultrasound has a more limited role in the assessment of urolithiasis compared with CT but has the distinct advantage of no associated ionizing radiation. Therefore, ultrasound should be considered as a screening tool in the workup for nonemergent abdominal or flank pain.

3.b. Given the size of the stone, it will most likely not pass, and planning for an endourological procedure is advisable. In managing stone disease in the pediatric population, it is important to note that renal calculi smaller than 3 mm are likely to spontaneously pass, and stones 4 mm or larger in the distal ureter are likely to require endourologic treatment. This information should be relayed to caregivers and parents.

4.a. Shockwave lithotripsy (SWL). Recent data suggest that stone free rates in children with a history of urologic condition or urinary tract reconstruction are quite low (12.5%) and may be better served with ureterorenoscopy or PCNL.

5.e. a, b, and c. SWL failure and retreatment rates were associated with increased mean stone burden, increased infundibular length, and infundibulopelvic angle greater than 45 degrees. Staghorn calculi are uncommon in children and represent a management challenge. Although monotherapy success rates are low in adults, acceptable stone-free rates in children have been achieved with SWL.

6.e. a and b. Irrigating fluid, which may be used under pressure, should be isotonic and body temperature to avoid hypothermia and hyponatremia

Other complications of ureteroscopy include unrecognized ureteral injury including mucosal flaps and tears, perforation, false passage, and partial to complete avulsion. Hypertension is not a recognized complication of ureteroscopy.

7.c. PCNL. This child would be best served with a PCNL because of the large stone burden. Although ureteroscopy is an option, multiple sessions would most likely be required. Cystine stones do not respond well to SWL.

Medical therapy helps to prevent cystine stones, not treat them. Anatrophic nephrolithotomy is not an appropriate surgical treatment for this stone.

8.b. Ammonium acid urate. Bladder stones are more often found in children from developing countries and are thought to be related endemically to malnutrition. It is thought that diets low in animal protein and phosphorus (breast milk as opposed to cow's milk) in addition to vitamin A deficiency are contributory. Bladder stones from children in these developing countries are most often composed of ammonium acid urate. In contrast, among children from industrialized nations, bladder stones are most often found in those with spinal cord injuries or congenital abnormalities such as spina bifida. Very often these children have undergone augment cystoplasty and/or manage their bladders by clean intermittent catheterization.

Chapter review

1.Although reference ranges for 24-hour urine metabolites in children who form stones are not standardized, initial workup should include a 24hour urine for creatinine, sodium, calcium, oxalate, uric acid, and citrate.

2.A metabolic abnormality is often present in pediatric stone formers; hypocitraturia is the most common abnormality.

3.An unenhanced helical CT scan is the imaging modality of choice in a patient with a suspected stone or in a known stone former; however, ultrasound should be used as a screen in a patient with nonemergent abdominal or flank pain to limit radiation exposure.

4.There has been a dramatic increase in pediatric nephrolithiasis, especially among white adolescent females.

5.Renal/ureteral calculi smaller than 3 mm are likely to spontaneously pass; calculi larger than 4 mm usually require endourologic management.

6.There is a theoretical risk that children treated with SWL will develop diabetes or hypertension.

7.Perioperative antibiotics are indicated for those patients requiring urologic instrumentation.

8.SWL has been the preferred treatment for proximal ureteral and renal calculi smaller than 15 mm.

9.Ureteral stenting after a procedure should be considered in patients with solitary kidneys, staghorn calculi, large ureteral calculi, prior obstruction, or abnormal anatomy. It may also be used to dilate the small ureter prior to ureteroscopy.

10.SWL has a poor success rate for stones with densities greater than 1000 Hounsfield units and those with previous urinary tract reconstruction.

11.Dilation of the pediatric ureter does not result in an unacceptable risk of the development of reflux or stricture.

12.Contraindications for ureteroscopic stone management include staghorn calculi, recurrent stone formers amenable to PCNL, and those with anatomic abnormalities precluding retrograde access.

13.Distal ureteral stones are best managed ureteroscopically.

14.Ureteroscopy should be performed under general anesthesia with the patient paralyzed. Isotonic body-temperature fluids should be used for the irrigant.

15.The most common complication of ureteroscopy is an unrecognized ureteral injury.

16.Indications for PCNL include a stone burden greater than 1.5 cm, lower pole calculi greater than 1.0 cm, calculi of cystine or struvite composition, and anatomic abnormalities making stone clearance difficult.

17.Spinal deformities may alter the anatomic location of the kidney, increasing the incidence of adjacent organ injury during percutaneous access.

18.Bladder stones in children in underdeveloped countries are due to malnutrition—a diet low in animal protein, phosphorus, and vitamin A —and usually consist of ammonium acid urate. In developed countries, bladder calculi are usually due to a neurogenic bladder or a reconstructed bladder.

19.Fifty percent of children with a reconstructed bladder will develop stones. Factors that play a role include stasis, bacterial colonization, retained mucus, or foreign body. The composition is usually struvite.

20.Percutaneous cystolithotripsy is the preferred method of managing

bladder calculi in children.

SECTION D

Lower Urinary Tract Conditions